Semi-Annual Consolidated Balance Sheet
| Concept | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2024-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2023-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | As at 2022-12-20 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Semi-annual consolidated balance sheet | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Balance sheet | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Current assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cash and deposits | 
                                                1,217,736,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                1,389,169,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,132,286,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,279,784,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Securities | 
                                                100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                50,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                50,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | 
                                                21,572,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                99,951,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                19,769,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                36,184,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Allowance for doubtful accounts | 
                                                -386,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                -368,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -415,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -382,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current assets | 
                                                2,238,789,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                2,538,830,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,267,387,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,534,859,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Property, plant and equipment | 
                                                1,338,237,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                1,422,959,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,322,415,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,402,975,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Property, plant and equipment | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Buildings and structures | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Buildings and structures, net | — | — | — | — | — | — | — | — | — | — | — | 
                                                275,360,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                293,197,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Machinery, equipment and vehicles | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Machinery, equipment and vehicles, net | — | — | — | — | — | — | — | — | — | — | — | 
                                                212,012,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                173,161,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Land | 
                                                831,804,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                903,724,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                834,504,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                906,424,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other, net | — | — | — | — | — | — | — | — | — | — | — | 
                                                31,862,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                30,191,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Accumulated depreciation | — | — | — | — | — | — | — | — | — | — | — | 
                                                -2,743,033,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -2,694,009,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Intangible assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Other | — | — | — | — | — | — | — | — | — | — | — | 
                                                57,397,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                78,512,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Intangible assets | 
                                                57,355,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                57,397,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                78,395,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                78,512,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Investments and other assets | 
                                                763,757,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                524,499,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                830,813,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                561,570,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Investments and other assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Investment securities | 
                                                338,775,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                338,775,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                343,739,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                343,739,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Deferred tax assets | 
                                                2,501,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                5,042,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                38,997,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                42,406,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | 
                                                38,686,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                57,051,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                38,703,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                56,220,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Allowance for doubtful accounts | 
                                                -3,652,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                -3,652,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -4,012,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -4,012,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current assets | 
                                                2,159,350,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                2,004,857,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,231,624,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,043,057,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Assets | 
                                                4,398,140,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,217,005,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                2,326,682,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,543,687,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                299,342,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,445,887,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                374,443,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                97,330,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
                                                4,499,011,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,338,138,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                4,577,917,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                538,315,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                294,600,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,239,778,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,408,892,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                96,329,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Liabilities | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Current liabilities | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Short-term borrowings | 
                                                70,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                371,179,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                70,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                339,166,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Income taxes payable | 
                                                12,250,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                20,256,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                12,944,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                16,108,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | 
                                                249,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                284,105,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                226,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                273,768,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current liabilities | 
                                                889,500,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                851,393,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                911,615,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                851,721,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current liabilities | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Long-term borrowings | 
                                                321,746,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                321,746,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                414,747,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                414,747,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Retirement benefit liability | — | — | — | — | — | — | — | — | — | — | — | 
                                                539,711,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                520,696,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Asset retirement obligations | 
                                                9,247,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                9,247,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                9,247,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                9,247,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current liabilities | 
                                                1,135,504,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                1,160,910,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,164,153,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,186,957,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Liabilities | 
                                                2,025,005,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                2,012,303,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,075,769,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,038,679,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Provision for retirement benefits for directors (and other officers) | 
                                                164,370,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                164,370,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                164,370,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                164,370,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Net assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Share capital | 
                                                822,195,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                822,195,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                815,198,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                815,198,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Shareholders' equity | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Capital surplus | 
                                                945,495,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                945,495,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                938,498,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                938,498,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Retained earnings | 
                                                485,098,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                559,362,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                619,845,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                656,978,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Treasury shares | 
                                                -116,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                -116,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -116,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -116,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Shareholders' equity | 
                                                2,252,673,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                2,326,936,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,373,425,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,410,559,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Valuation and translation adjustments | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Valuation difference on available-for-sale securities | 
                                                120,461,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                120,461,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                49,817,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                49,817,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Foreign currency translation adjustment | — | — | — | — | — | — | — | — | — | — | — | 
                                                52,102,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                48,202,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Valuation and translation adjustments | 
                                                120,461,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                172,563,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                49,817,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                98,019,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-controlling interests | — | — | — | — | — | — | — | — | — | — | — | 
                                                31,883,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                30,659,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Net assets | 
                                                2,373,134,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -116,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                822,195,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                945,495,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                172,563,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,326,936,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                120,461,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                120,461,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -116,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,531,383,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                945,495,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                52,102,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                120,461,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                822,195,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                31,883,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                945,495,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                485,098,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                559,362,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                10,412,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,252,673,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                474,686,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                815,198,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                49,817,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,410,559,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                49,817,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                98,019,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                48,202,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,423,242,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                938,498,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,539,238,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                30,659,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                815,198,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                10,412,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,373,425,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                938,498,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                656,978,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                609,432,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                938,498,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -116,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                619,845,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                49,817,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -116,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                43,023,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                938,498,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                938,498,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,523,045,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                801,351,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                938,498,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                83,447,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -116,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                43,023,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                769,465,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                10,412,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,667,125,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                40,424,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -116,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                815,198,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                815,198,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                759,052,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                28,746,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                43,023,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,554,931,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,566,069,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Liabilities and net assets | 
                                                4,398,140,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                4,543,687,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                4,499,011,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                4,577,917,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — |