Key Financial Data Of Reporting Company
| Concept | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 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 | As at 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 | — | — | — | 
                                                11,094,810,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                12,409,590,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                11,397,375,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                10,056,826,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                10,599,063,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                9,489,710,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                19,637,138,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                20,536,537,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                21,351,579,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                20,489,291,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Ordinary profit (loss) | — | — | — | 
                                                315,809,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                239,630,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                126,609,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                37,284,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -41,144,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -125,352,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -7,344,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                36,056,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                272,528,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                244,635,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Profit (loss) | — | — | — | 
                                                310,373,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                47,374,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                -530,606,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -64,639,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                174,612,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Share capital | — | — | 
                                                573,977,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                572,374,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                569,449,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                567,326,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                386,305,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Total number of issued shares | — | — | 
                                                9,860,500
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                9,855,300
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                9,832,900
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                9,814,900
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | — | 
                                                9,127,500
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
| Net assets | — | — | 
                                                2,832,837,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                2,920,467,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,767,312,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,587,885,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,775,768,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,627,903,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,246,390,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,363,025,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,046,329,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                3,151,806,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Total assets | — | — | 
                                                6,955,505,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                7,463,366,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                7,281,524,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                6,752,061,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                7,125,173,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                6,756,153,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                6,531,417,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                6,833,067,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                6,531,261,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                6,799,998,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net assets per share | — | — | 
                                                289.18
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                298.27
                                                
                                             | — | 
                                                282.15
                                                
                                             | — | 
                                                263.52
                                                
                                             | 
                                                280.02
                                                
                                             | — | 
                                                264.77
                                                
                                             | — | — | 
                                                328.51
                                                
                                             | 
                                                340.56
                                                
                                             | — | — | 
                                                330.05
                                                
                                             | — | 
                                                341.78
                                                
                                             | 
| Dividend paid per share | — | — | — | 
                                                7.00
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                7.00
                                                
                                             | — | — | — | — | 
                                                7.00
                                                
                                             | 
                                                9.00
                                                
                                             | — | — | — | — | — | 
                                                9.00
                                                
                                             | — | 
| Interim dividend paid per share | — | — | — | 
                                                3.50
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                3.50
                                                
                                             | — | — | — | — | 
                                                4.50
                                                
                                             | 
                                                4.50
                                                
                                             | — | — | — | — | — | 
                                                4.50
                                                
                                             | — | 
| Basic earnings (loss) per share | — | — | — | 
                                                32.20
                                                
                                             | 
                                                22.66
                                                
                                             | — | — | — | — | — | — | — | 
                                                8.13
                                                
                                             | — | 
                                                4.88
                                                
                                             | — | — | 
                                                -51.50
                                                
                                             | — | 
                                                -54.72
                                                
                                             | 
                                                -6.91
                                                
                                             | — | — | 
                                                -5.72
                                                
                                             | 
                                                20.47
                                                
                                             | — | 
                                                19.60
                                                
                                             | — | 
| Diluted earnings per share | — | — | — | 
                                                32.00
                                                
                                             | 
                                                22.52
                                                
                                             | — | — | — | — | — | — | — | 
                                                8.03
                                                
                                             | — | 
                                                4.82
                                                
                                             | — | — |  | — |  |  | — | — |  | 
                                                19.87
                                                
                                             | — | 
                                                19.02
                                                
                                             | — | 
| Equity-to-asset ratio | — | — | 
                                                0.401
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                0.385
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.373
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.376
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.381
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.380
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.487
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.483
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.455
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.452
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Rate of return on equity | — | — | — | 
                                                0.1165
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.0781
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                0.0291
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.0186
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                -0.1661
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                -0.1846
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                -0.0210
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                -0.0168
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.0614
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.0609
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Price-earnings ratio | — | — | — | 
                                                9.07
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                12.88
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                38.03
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                63.37
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                27.36
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                28.57
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Payout ratio | — | — | — | 
                                                0.217
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                1.436
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | 
                                                0.459
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Net cash provided by (used in) operating activities | — | — | — | — | 
                                                198,288,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                393,624,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                -737,495,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                76,607,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                259,883,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
| Net cash provided by (used in) investing activities | — | — | — | — | 
                                                -30,748,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                10,024,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                -399,406,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                -83,322,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -31,622,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
| Net cash provided by (used in) financing activities | — | — | — | — | 
                                                -333,254,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                -384,379,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                614,898,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                -31,377,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                597,448,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
| Cash and cash equivalents | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,358,821,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,524,536,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,505,267,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                3,027,270,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                3,065,362,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Number of employees | 
                                                7
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                30
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                190
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                22
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                138
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                22
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                263
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                30
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                322
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                273
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                193
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                268
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                218
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                228
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                288
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                212
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                269
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                10
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                31
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                15
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                16
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                10
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                33
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                31
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                29
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                28
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                26
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                26
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                28
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                30
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                31
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Total shareholder return | — | — | 
                                                0.451
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                0.464
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.658
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.748
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | 
                                                0.770
                                                
                                                    
                                                        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
                                                    
                                                
                                             | — | — |