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 | ||||||
| Net sales | — | 
                                                431,527,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,523,120,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                394,098,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Ordinary profit (loss) | — | 
                                                -21,038,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                143,037,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                114,879,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Profit (loss) | — | 
                                                -19,290,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                59,491,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                73,333,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Equity in earnings (losses) of affiliates if equity method is applied | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Share capital | 
                                                370,665,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                370,618,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                369,890,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total number of issued shares | 
                                                8,217,900
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                8,207,100
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                8,136,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
| Net assets | 
                                                1,359,048,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,378,084,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,390,307,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | 
                                                3,119,339,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,224,518,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,839,419,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Dividend paid per share | — |  |  | — | — |  | 
| Basic earnings (loss) per share | — | 
                                                -2.35
                                                
                                             | 
                                                7.29
                                                
                                             | — | — | 
                                                9.01
                                                
                                             | 
| Diluted earnings per share | — |  | 
                                                6.97
                                                
                                             | — | — | 
                                                8.63
                                                
                                             | 
| Equity-to-asset ratio | 
                                                0.436
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.427
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.490
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |