Key Financial Data Of Reporting Company
| Concept | As at 2023-12-31 | 2023-10-01 to 2023-12-31 | 2023-04-01 to 2023-12-31 | As at 2023-03-31 | 2022-04-01 to 2023-03-31 | 2022-04-01 to 2022-12-31 | As at 2022-12-31 | 2022-10-01 to 2022-12-31 | 
|---|---|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||||
| Business results of reporting company | ||||||||
| Revenue | — | — | 
                                                7,354,878,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                9,960,242,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                7,091,286,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Ordinary profit (loss) | — | — | 
                                                455,517,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                621,019,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                346,130,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Profit (loss) | — | — | 
                                                286,529,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                82,316,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                212,247,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Equity in earnings (losses) of affiliates if equity method is applied | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Share capital | 
                                                923,761,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                923,761,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                923,761,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total number of issued shares | 
                                                4,720,245
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                4,720,245
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                4,720,245
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
| Net assets | 
                                                7,301,141,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                7,292,198,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                7,425,344,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | 
                                                13,522,693,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                13,762,244,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                13,338,169,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Dividend paid per share | — | — | 
                                                30.00
                                                
                                             | — | 
                                                60.00
                                                
                                             | 
                                                30.00
                                                
                                             | — | — | 
| Basic earnings (loss) per share | — | 
                                                21.13
                                                
                                             | 
                                                60.70
                                                
                                             | — | 
                                                17.44
                                                
                                             | 
                                                44.97
                                                
                                             | — | 
                                                15.30
                                                
                                             | 
| Diluted earnings per share | — | — |  | — |  |  | — | — | 
| Equity-to-asset ratio | 
                                                0.540
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.530
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.557
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |