Key Financial Data Of Reporting Company
| Concept | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | 2024-01-01 to 2024-12-31 | As at 2024-12-31 | 2024-01-01 to 2024-12-31 | As at 2024-12-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | 2023-01-01 to 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 | 2022-01-01 to 2022-12-31 | 2021-01-01 to 2021-12-31 | 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 | 2020-01-01 to 2020-12-31 | As at 2020-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||||||||||||||||||||||
| Business results of reporting company | ||||||||||||||||||||||||||
| Net sales | — | — | — | — | — | — | 
                                                5,040,565,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                5,040,565,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                5,108,295,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                5,108,295,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                5,354,154,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                5,354,154,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,325,485,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                5,331,176,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,309,801,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                5,279,223,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Ordinary profit (loss) | — | — | — | — | — | — | 
                                                -113,699,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                366,816,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -44,339,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -113,493,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                14,478,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                110,225,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                165,634,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                167,815,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -231,168,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -61,251,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Profit (loss) | — | — | — | — | — | — | 
                                                -30,860,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                -177,599,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                135,970,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                969,308,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                -163,314,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Share capital | — | — | 
                                                100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                2,550,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Total number of issued shares | — | — | 
                                                18,688,540
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                18,688,540
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                18,688,540
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                18,688,540
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | — | 
                                                18,688,540
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
| Net assets | — | — | 
                                                2,289,245,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                2,303,753,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,367,645,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,409,469,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,459,768,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,599,433,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,512,627,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,258,875,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,570,644,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,308,832,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Total assets | — | — | 
                                                5,770,976,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                5,785,432,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                7,459,478,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                7,504,936,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                8,001,523,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                8,122,755,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                8,256,686,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                8,079,852,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                8,868,433,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                6,864,637,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net assets per share | — | — | 
                                                160.34
                                                
                                             | — | — | — | — | — | — | 
                                                159.96
                                                
                                             | — | 
                                                211.85
                                                
                                             | — | 
                                                214.48
                                                
                                             | 
                                                217.65
                                                
                                             | — | 
                                                226.44
                                                
                                             | — | — | 
                                                220.98
                                                
                                             | 
                                                205.00
                                                
                                             | — | — | 
                                                158.27
                                                
                                             | — | 
                                                80.50
                                                
                                             | 
| Dividend paid per share | — | — | — | — | — | — | 
                                                25.00
                                                
                                             | — | — | — | — | — |  | — | — | — | — | 
                                                2.50
                                                
                                             | 
                                                5.00
                                                
                                             | — | — | — | — | — |  | — | 
| Interim dividend paid per share | — | — | — | — | — | — | 
                                                20.00
                                                
                                             | — | — | — | — | — |  | — | — | — | — |  |  | — | — | — | — | — |  | — | 
| Basic earnings (loss) per share | — | — | — | — | — | — | 
                                                -1.97
                                                
                                             | — | 
                                                32.46
                                                
                                             | — | 
                                                -6.83
                                                
                                             | — | 
                                                -11.18
                                                
                                             | — | — | 
                                                2.53
                                                
                                             | — | 
                                                8.56
                                                
                                             | 
                                                59.94
                                                
                                             | — | — | 
                                                132.20
                                                
                                             | 
                                                -19.85
                                                
                                             | — | 
                                                -10.07
                                                
                                             | — | 
| Diluted earnings per share | — | — | — | — | — | — |  | — |  | — |  | — |  | — | — | 
                                                2.18
                                                
                                             | — | 
                                                6.95
                                                
                                             | 
                                                47.76
                                                
                                             | — | — | 
                                                105.14
                                                
                                             |  | — |  | — | 
| Equity-to-asset ratio | — | — | 
                                                0.397
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                0.395
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.451
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.454
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.432
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.443
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.425
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.403
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.290
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.190
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Rate of return on equity | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.180
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.012
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.038
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.319
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.937
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Price-earnings ratio | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                12.1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                46.6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                13.8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2.2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                1.0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Payout ratio | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
                                                0.292
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.083
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Net cash provided by (used in) operating activities | — | — | — | — | — | — | — | — | 
                                                233,445,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                257,533,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                -159,068,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                368,782,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                342,589,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
| Net cash provided by (used in) investing activities | — | — | — | — | — | — | — | — | 
                                                956,362,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                485,588,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                -649,511,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                2,247,525,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                194,788,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
| Net cash provided by (used in) financing activities | — | — | — | — | — | — | — | — | 
                                                -1,772,526,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -119,426,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                -209,152,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                -919,957,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -605,230,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
| Cash and cash equivalents | — | — | — | — | — | — | — | — | — | 
                                                1,620,089,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,121,417,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,459,762,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                2,224,956,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                452,866,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Number of employees | 
                                                16
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                34
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                145
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                96
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                15
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                36
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                96
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                148
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                149
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                149
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                160
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                160
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                164
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                164
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                163
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                169
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                17
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                37
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                17
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                17
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                17
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                37
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                45
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                45
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                44
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                44
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                33
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                33
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                50
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                50
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Total shareholder return | — | — | 
                                                2.849
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                0.768
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.842
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.913
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                0.872
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
| Total return on share price index | — | — | 
                                                1.825
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                1.515
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                1.181
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                1.211
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                1.074
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — |