Key Financial Data Of Reporting Company
| Concept | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2022-12-31 | 2022-01-01 to 2022-12-31 | As at 2022-12-31 | As at 2021-12-31 | As at 2021-12-31 | 2021-01-01 to 2021-12-31 | 2020-01-01 to 2020-12-31 | As at 2020-12-31 | As at 2020-12-31 | As at 2019-12-31 | 2019-01-01 to 2019-12-31 | As at 2019-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||||||||||||||
| Business results of reporting company | ||||||||||||||||||
| Net sales | 
                                                2,184,465,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                2,066,210,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,889,078,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,434,360,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                956,158,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Ordinary profit (loss) | 
                                                -45,978,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                -17,165,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                153,890,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -711,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                -402,104,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Profit (loss) | 
                                                -27,735,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                1,623,441,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                140,802,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                62,363,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                -2,132,807,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Share capital | — | — | — | 
                                                2,438,859,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                2,427,759,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,427,759,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                2,359,828,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,359,428,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Total number of issued shares | — | — | — | 
                                                15,965,800
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | — | — | 
                                                15,854,800
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                15,854,800
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | — | — | 
                                                15,668,200
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                15,664,200
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
| Net assets | — | — | — | 
                                                4,791,577,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                4,819,380,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,463,090,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                2,785,066,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,723,140,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Total assets | — | — | — | 
                                                6,230,910,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                6,292,798,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,624,224,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                3,577,869,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,432,783,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Net assets per share | — | — | — | 
                                                305.48
                                                
                                             | — | — | — | — | 
                                                309.44
                                                
                                             | 
                                                222.36
                                                
                                             | — | — | — | — | 
                                                178.94
                                                
                                             | 
                                                174.96
                                                
                                             | — | — | 
| Dividend paid per share |  | — | — | — | — | — | — |  | — | — | — |  |  | — | — | — |  | — | 
| Interim dividend paid per share |  | — | — | — | — | — | — |  | — | — | — |  |  | — | — | — |  | — | 
| Basic earnings (loss) per share | 
                                                -1.77
                                                
                                             | — | — | — | — | — | — | 
                                                104.24
                                                
                                             | — | — | — | 
                                                9.07
                                                
                                             | 
                                                4.05
                                                
                                             | — | — | — | 
                                                -138.74
                                                
                                             | — | 
| Diluted earnings per share |  | — | — | — | — | — | — | 
                                                103.82
                                                
                                             | — | — | — | 
                                                9.02
                                                
                                             | 
                                                4.03
                                                
                                             | — | — | — |  | — | 
| Equity-to-asset ratio | — | — | — | 
                                                0.769
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
                                                0.766
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.749
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
                                                0.770
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.784
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
| Rate of return on equity | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                0.392
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                0.045
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.023
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Price-earnings ratio | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                3.35
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                88.22
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                124.83
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Payout ratio | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Number of employees | — | 
                                                16
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                118
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                99
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                102
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                103
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                85
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                75
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                130
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                116
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                53
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                62
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                138
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | — | 
                                                8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                45
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                19
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                37
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                42
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                13
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                12
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                38
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                35
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                10
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                29
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Total shareholder return | — | — | — | 
                                                0.74
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
                                                0.84
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1.92
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
                                                1.22
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.87
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
| Total return on share price index | — | — | — | 
                                                0.87
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
                                                0.90
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1.22
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
                                                1.47
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1.10
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — |