Key Financial Data Of Reporting Company
| Concept | As at 2024-03-31 | 2024-01-01 to 2024-03-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | As at 2023-03-31 | 2023-01-01 to 2023-03-31 | 
|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||
| Business results of reporting company | ||||||
| Operating revenue | — | 
                                                333,153,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,369,551,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                373,601,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Ordinary profit (loss) | — | 
                                                11,855,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                120,158,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                62,675,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Profit (loss) | — | 
                                                3,628,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                73,191,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                39,423,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Equity in earnings (losses) of affiliates if equity method is applied | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Share capital | 
                                                328,066,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                319,256,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                316,523,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total number of issued shares | 
                                                3,906,600
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                3,885,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                3,873,200
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
| Net assets | 
                                                1,417,488,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,451,788,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,473,228,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | 
                                                2,734,886,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,013,606,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,139,099,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Dividend paid per share | — |  | 
                                                32.00
                                                
                                             | — | — |  | 
| Basic earnings (loss) per share | — | 
                                                0.94
                                                
                                             | 
                                                19.10
                                                
                                             | — | — | 
                                                10.32
                                                
                                             | 
| Diluted earnings per share | — | 
                                                0.94
                                                
                                             | 
                                                18.91
                                                
                                             | — | — | 
                                                10.19
                                                
                                             | 
| Equity-to-asset ratio | 
                                                0.518
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.480
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.467
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |