Key Financial Data Of Reporting Company
| Concept | As at 2023-12-31 | 2023-10-01 to 2023-12-31 | 2023-04-01 to 2023-12-31 | As at 2023-03-31 | 2022-04-01 to 2023-03-31 | 2022-04-01 to 2022-12-31 | As at 2022-12-31 | 2022-10-01 to 2022-12-31 | 
|---|---|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||||
| Business results of reporting company | ||||||||
| Net sales | — | — | 
                                                4,170,232,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                6,020,260,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,258,988,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Ordinary profit (loss) | — | — | 
                                                109,557,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                310,574,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                205,929,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Profit (loss) | — | — | 
                                                75,229,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                252,477,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                135,561,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Equity in earnings (losses) of affiliates if equity method is applied | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Share capital | 
                                                664,740,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                664,740,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                664,740,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total number of issued shares | 
                                                4,022,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                4,022,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                4,022,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
| Net assets | 
                                                3,035,366,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,012,504,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,895,509,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | 
                                                5,616,068,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                6,062,236,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                6,182,350,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Dividend paid per share | — | — |  | — | 
                                                16.0
                                                
                                             |  | — | — | 
| Basic earnings (loss) per share | — | 
                                                7.53
                                                
                                             | 
                                                19.98
                                                
                                             | — | 
                                                67.27
                                                
                                             | 
                                                36.13
                                                
                                             | — | 
                                                20.89
                                                
                                             | 
| Diluted earnings per share | — | — |  | — |  |  | — | — | 
| Equity-to-asset ratio | 
                                                0.540
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.497
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.468
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |