Key Financial Data Of Reporting Company
| Concept | 
                                    
                                        2024-01-01 to 2024-06-30  | 
                            
                                
                                    
                                        As at 2024-06-30  | 
                            
                                
                                    
                                        2023-01-01 to 2023-12-31  | 
                            
                                
                                    
                                        As at 2023-12-31  | 
                            
                                
                                    
                                        2023-01-01 to 2023-06-30  | 
                            
                                
                                    
                                        As at 2023-06-30  | 
                            
                        
|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||
| Business results of reporting company | ||||||
| Net sales | 
                                        
                                             
                                                1,983,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                3,222,096,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                1,413,922,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Ordinary profit (loss) | 
                                        
                                             
                                                112,758,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                115,513,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                38,269,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Net assets | — | 
                                        
                                             
                                                1,310,594,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                1,189,958,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                1,094,229,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Total assets | — | 
                                        
                                             
                                                3,178,719,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                3,289,194,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                2,570,717,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Basic earnings (loss) per share | 
                                        
                                             
                                                33.97
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                43.18
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                12.24
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Diluted earnings per share | 
                                        
                                             
                                                31.71
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                39.97
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                11.15
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Equity-to-asset ratio | — | 
                                        
                                             
                                                0.412
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                0.361
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                0.425
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Net cash provided by (used in) operating activities | 
                                        
                                             
                                                -142,497,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                -11,082,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                -164,069,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Net cash provided by (used in) investing activities | 
                                        
                                             
                                                -47,504,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                -110,871,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                -1,856,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Net cash provided by (used in) financing activities | 
                                        
                                             
                                                -103,204,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                612,053,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                488,835,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
| Cash and cash equivalents | — | 
                                        
                                             
                                                1,378,691,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                1,671,898,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | 
                                        
                                             
                                                1,504,708,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             
                                        
                                     |