Semi-Annual Consolidated Balance Sheet
| Concept | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2021-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Semi-annual consolidated balance sheet | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Balance sheet | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Assets | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Current assets | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cash and deposits | — | — | — | — | — | 
                                                336,757,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                422,490,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                569,057,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                479,240,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                14,553,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                5,178,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                1,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Allowance for doubtful accounts | — | — | — | — | — | 
                                                -4,597,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                -4,596,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current assets | — | — | — | — | — | 
                                                2,904,652,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                3,597,224,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                3,188,682,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                2,489,466,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current assets | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Property, plant and equipment | — | — | — | — | — | 
                                                1,178,249,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                1,836,867,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,895,236,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                1,201,890,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Property, plant and equipment | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Buildings and structures | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Buildings and structures, net | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                637,666,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                660,645,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Machinery, equipment and vehicles | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Machinery, equipment and vehicles, net | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                424,581,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                462,619,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Land | — | — | — | — | — | 
                                                526,994,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                732,441,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                732,441,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                526,994,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other, net | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                42,177,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                39,530,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Accumulated depreciation | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -5,197,398,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -5,163,554,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Intangible assets | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Other | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                19,248,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                0
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Intangible assets | — | — | — | — | — | 
                                                15,116,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                36,490,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                11,203,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                6,870,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Investments and other assets | — | — | — | — | — | 
                                                143,362,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                125,262,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                136,246,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                154,440,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Investments and other assets | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Investment securities | — | — | — | — | — | 
                                                226,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                226,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                226,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                226,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Deferred tax assets | — | — | — | — | — | 
                                                9,639,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                9,638,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                22,051,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                22,146,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | 
                                                95,115,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                114,739,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                112,077,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                89,188,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Allowance for doubtful accounts | — | — | — | — | — | 
                                                -11,831,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                -11,831,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -11,796,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                -11,796,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current assets | — | — | — | — | — | 
                                                1,336,728,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                1,998,621,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,042,686,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                1,363,201,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Assets | — | — | — | — | — | 
                                                4,241,380,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                5,032,402,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                563,443,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,723,921,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,595,845,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,308,480,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                3,185,297,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,338,450,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,523,747,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,231,369,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                707,621,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,852,668,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Liabilities | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Current liabilities | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Notes and accounts payable - trade | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                715,356,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                704,530,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Short-term borrowings | — | — | — | — | — | 
                                                1,594,462,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                1,804,084,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,600,989,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                1,416,625,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Income taxes payable | — | — | — | — | — | 
                                                34,301,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                44,499,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                27,677,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                6,546,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | 
                                                29,158,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                94,364,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                156,583,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                121,558,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current liabilities | — | — | — | — | — | 
                                                2,545,115,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                3,124,185,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,873,761,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                2,349,627,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current liabilities | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Long-term borrowings | — | — | — | — | — | 
                                                645,633,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                999,316,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                972,638,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                493,380,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Retirement benefit liability | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                181,399,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                173,649,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Asset retirement obligations | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                249,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                3,569,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                3,320,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current liabilities | — | — | — | — | — | 
                                                813,546,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                1,214,378,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,173,629,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                654,138,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Liabilities | — | — | — | — | — | 
                                                3,358,661,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                4,338,564,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                4,047,391,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                3,003,766,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Provision for retirement benefits for directors (and other officers) | — | — | — | — | — | 
                                                14,100,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                29,147,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                19,947,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                6,900,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Provision for bonuses | — | — | — | — | — | 
                                                68,945,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                72,064,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                24,905,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                20,478,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Deferred tax liabilities | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                4,266,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                3,824,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Provision for bonuses for directors (and other officers) | — | — | — | — | — | 
                                                5,610,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                6,910,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Net assets | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Shareholders' equity | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Share capital | — | — | — | — | — | 
                                                615,216,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                615,216,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                615,216,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                615,216,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Capital surplus | — | — | — | — | — | 
                                                45,868,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                76,094,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                76,223,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                45,997,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Retained earnings | — | — | — | — | — | 
                                                262,837,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                607,174,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                533,561,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                228,712,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Treasury shares | — | — | — | — | — | 
                                                -41,203,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                -41,203,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -41,024,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                -41,024,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Shareholders' equity | — | — | — | — | — | 
                                                882,719,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                1,257,281,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,183,977,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                848,902,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Net assets | 
                                                615,216,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                615,216,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                116,837,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,686,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,257,281,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                882,719,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                76,094,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                45,868,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -41,203,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,257,281,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                40,181,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -41,203,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                882,719,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                607,174,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                262,837,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                146,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                40,181,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -41,024,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -41,024,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                228,712,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,816,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                615,216,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,183,977,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                76,223,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,183,977,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                146,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                615,216,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                848,902,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                533,561,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                82,712,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                45,997,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                848,902,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                615,216,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,206,108,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                47,853,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                615,216,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                120,061,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                40,181,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                14,816,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,143,439,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                872,391,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                537,109,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                14,816,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                40,181,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                40,181,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -49,068,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                14,816,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                14,816,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                266,061,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                887,207,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -49,068,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                146,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Liabilities and net assets | — | — | — | — | — | 
                                                4,241,380,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                5,595,845,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                5,231,369,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                3,852,668,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — |