Key Financial Data Of Reporting Company
| Concept | As at 2023-09-30 | 2023-01-01 to 2023-09-30 | 2023-07-01 to 2023-09-30 | 2022-01-01 to 2022-12-31 | As at 2022-12-31 | 2022-01-01 to 2022-09-30 | As at 2022-09-30 | 2022-07-01 to 2022-09-30 | 
|---|---|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||||
| Business results of reporting company | ||||||||
| Operating revenue | — | 
                                                1,020,513,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,466,689,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,098,423,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Ordinary profit (loss) | — | 
                                                66,734,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                238,487,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                160,584,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Profit (loss) | — | 
                                                41,733,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                175,952,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                108,780,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Equity in earnings (losses) of affiliates if equity method is applied | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Share capital | 
                                                319,256,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                315,771,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                315,019,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total number of issued shares | 
                                                3,885,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | — | 
                                                3,865,200
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
                                                3,857,200
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
| Net assets | 
                                                1,431,758,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,499,929,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,468,059,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | 
                                                2,919,129,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                2,976,646,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,955,365,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Dividend paid per share | — | 
                                                17.00
                                                
                                             | — | 
                                                30.00
                                                
                                             | — | 
                                                15.00
                                                
                                             | — | — | 
| Basic earnings (loss) per share | — | 
                                                10.90
                                                
                                             | 
                                                2.90
                                                
                                             | 
                                                45.85
                                                
                                             | — | 
                                                28.35
                                                
                                             | — | 
                                                8.12
                                                
                                             | 
| Diluted earnings per share | — | 
                                                10.78
                                                
                                             | — | 
                                                44.86
                                                
                                             | — | 
                                                27.70
                                                
                                             | — | — | 
| Equity-to-asset ratio | 
                                                0.488
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                0.502
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.494
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |