Key Financial Data Of Reporting Company
| Concept | As at 2024-06-30 | 2024-01-01 to 2024-06-30 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | As at 2023-06-30 | 2023-01-01 to 2023-06-30 | 
|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||
| Business results of reporting company | ||||||
| Net sales | — | 
                                                1,618,332,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,640,002,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,759,053,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Ordinary profit (loss) | — | 
                                                76,182,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                533,438,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                301,014,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Profit (loss) | — | 
                                                49,248,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                363,695,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                188,161,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Equity in earnings (losses) of affiliates if equity method is applied | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Share capital | 
                                                817,533,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                807,609,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                790,459,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total number of issued shares | 
                                                5,597,700
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                5,503,600
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                5,330,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
| Net assets | 
                                                2,930,272,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,861,174,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,651,341,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | 
                                                4,872,736,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                4,980,604,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,800,995,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Dividend paid per share | — |  |  | — | — |  | 
| Basic earnings (loss) per share | — | 
                                                8.83
                                                
                                             | 
                                                67.87
                                                
                                             | — | — | 
                                                35.33
                                                
                                             | 
| Diluted earnings per share | — | 
                                                8.77
                                                
                                             | 
                                                65.29
                                                
                                             | — | — | 
                                                34.01
                                                
                                             | 
| Equity-to-asset ratio | 
                                                0.601
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.574
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.552
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Net cash provided by (used in) operating activities | — | 
                                                649,668,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                389,555,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                344,391,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) investing activities | — | 
                                                -65,922,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -717,953,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -602,378,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) financing activities | — | 
                                                -118,700,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                325,079,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                368,561,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Cash and cash equivalents | 
                                                768,289,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                303,243,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                417,134,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — |