Quarterly Consolidated Balance Sheet
| Concept | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | 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 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Quarterly consolidated balance sheet | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Balance sheet | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Current assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cash and deposits | — | — | — | — | — | — | — | — | — | — | — | 
                                                734,136,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                699,716,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                555,551,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                614,164,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Merchandise and finished goods | — | — | — | — | — | — | — | — | — | — | — | 
                                                45,458,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                27,538,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                24,078,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                43,420,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Work in process | — | — | — | — | — | — | — | — | — | — | — | 
                                                143,028,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                143,028,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                135,987,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                135,987,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Raw materials and supplies | — | — | — | — | — | — | — | — | — | — | — | 
                                                133,427,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                112,244,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                117,381,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                138,606,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | — | — | — | — | — | — | 
                                                15,763,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                3,787,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                7,925,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                10,100,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Allowance for doubtful accounts | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -161,706,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                -152,512,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current assets | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,262,120,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,219,382,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                1,115,976,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                1,165,293,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Property, plant and equipment | — | — | — | — | — | — | — | — | — | — | — | 
                                                135,817,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                135,817,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                119,277,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                119,277,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Property, plant and equipment | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Buildings and structures | — | — | — | — | — | — | — | — | — | — | — | 
                                                776,406,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                773,106,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Accumulated depreciation | — | — | — | — | — | — | — | — | — | — | — | 
                                                -773,204,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -773,106,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Buildings and structures, net | — | — | — | — | — | — | — | — | — | — | — | 
                                                3,201,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Machinery, equipment and vehicles | — | — | — | — | — | — | — | — | — | — | — | 
                                                73,580,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                70,472,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Accumulated depreciation | — | — | — | — | — | — | — | — | — | — | — | 
                                                -70,705,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -70,472,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Machinery, equipment and vehicles, net | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,875,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Land | — | — | — | — | — | — | — | — | — | — | — | 
                                                118,674,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                118,674,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                119,277,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                119,277,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | — | — | — | — | — | — | 
                                                523,218,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                510,358,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Accumulated depreciation | — | — | — | — | — | — | — | — | — | — | — | 
                                                -512,152,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -510,358,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other, net | — | — | — | — | — | — | — | — | — | — | — | 
                                                11,066,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Intangible assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Intangible assets | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,291,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                2,291,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Investments and other assets | — | — | — | — | — | — | — | — | — | — | — | 
                                                218,352,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                227,726,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                159,247,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                149,766,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Investments and other assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Investment securities | — | — | — | — | — | — | — | — | — | — | — | 
                                                95,058,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                95,058,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                95,225,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                95,225,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Deferred tax assets | — | — | — | — | — | — | — | — | — | — | — | 
                                                67,908,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                67,908,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | — | — | — | — | — | — | 
                                                55,385,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                17,568,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                18,678,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                54,540,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Allowance for doubtful accounts | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                -100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current assets | — | — | — | — | — | — | — | — | — | — | — | 
                                                356,461,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                365,835,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                278,524,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                269,044,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Assets | — | — | — | — | — | 
                                                42,102,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,576,479,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,618,582,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,618,582,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,585,218,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                1,394,501,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,434,337,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                57,177,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,434,337,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,377,160,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Liabilities | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Current liabilities | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Notes and accounts payable - trade | — | — | — | — | — | — | — | — | — | — | — | 
                                                4,345,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                5,697,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Short-term borrowings | — | — | — | — | — | — | — | — | — | — | — | 
                                                135,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                130,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Income taxes payable | — | — | — | — | — | — | — | — | — | — | — | 
                                                5,854,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                5,435,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                25,378,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                25,874,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | — | — | — | — | — | — | — | — | 
                                                64,959,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                59,377,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current liabilities | — | — | — | — | — | — | — | — | — | — | — | 
                                                257,824,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                216,610,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                212,118,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                252,005,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current liabilities | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Long-term borrowings | — | — | — | — | — | — | — | — | — | — | — | 
                                                84,561,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                68,331,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                80,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                99,101,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Retirement benefit liability | — | — | — | — | — | — | — | — | — | — | — | 
                                                7,763,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                4,614,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Asset retirement obligations | — | — | — | — | — | — | — | — | — | — | — | 
                                                3,122,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                3,122,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current liabilities | — | — | — | — | — | — | — | — | — | — | — | 
                                                95,446,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                93,496,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                93,965,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                103,715,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Liabilities | — | — | — | — | — | 
                                                56,382,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                296,888,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                353,270,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                353,270,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                310,107,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                306,084,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                355,720,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                56,361,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                355,720,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                299,359,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Net assets | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Shareholders' equity | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Share capital | — | — | — | — | — | — | — | — | — | — | — | 
                                                50,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                50,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                3,029,041,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                3,029,041,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Capital surplus | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,040,407,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,040,407,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                2,061,421,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                2,061,421,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Retained earnings | — | — | — | — | — | — | — | — | — | — | — | 
                                                176,894,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                186,694,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                -4,000,056,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                -4,009,856,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Treasury shares | — | — | — | — | — | — | — | — | — | — | — | 
                                                -1,990,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                -1,990,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                -1,990,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                -1,990,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Shareholders' equity | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,265,311,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,275,111,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                1,088,416,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                1,078,616,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Net assets | 
                                                1,275,111,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,040,407,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,040,407,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -1,990,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                186,694,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,990,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,040,407,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                50,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,265,311,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,265,311,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,275,111,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                50,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                176,894,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                186,694,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,029,041,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,029,041,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -4,000,056,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,078,616,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,088,416,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,061,421,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,061,421,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,990,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,078,616,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,061,421,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -1,990,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,088,416,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -4,009,856,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -4,000,056,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,061,421,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -1,990,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -1,990,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -3,369,088,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,029,041,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,368,348,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,061,421,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,368,348,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,029,041,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,719,385,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -3,720,124,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -3,369,088,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,061,421,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,719,385,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Liabilities and net assets | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,618,582,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,585,218,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                1,394,501,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                1,434,337,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — |