Key Financial Data Of Reporting Company
| Concept | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | 2022-01-01 to 2022-12-31 | As at 2022-12-31 | As at 2021-12-31 | 2021-01-01 to 2021-12-31 | 2020-01-01 to 2020-12-31 | As at 2020-12-31 | As at 2019-12-31 | 2019-01-01 to 2019-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|
| Key financial data of reporting company | ||||||||||
| Business results of reporting company | ||||||||||
| Net sales | 
                                                10,989,735,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                17,581,830,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                13,137,318,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,205,453,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                6,427,602,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Ordinary profit (loss) | 
                                                5,292,472,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                11,070,886,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                6,700,486,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                415,172,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,111,126,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Profit (loss) | 
                                                3,774,239,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                7,838,094,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                4,816,772,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                306,346,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                874,344,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Equity in earnings (losses) of affiliates if equity method is applied | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Share capital | — | 
                                                464,548,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                464,548,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                464,548,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                464,548,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                464,548,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total number of issued shares | — | 
                                                9,525,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
                                                9,525,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                9,525,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                9,525,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                9,525,000
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
| Net assets | — | 
                                                15,675,789,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                14,282,703,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                8,028,641,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,783,635,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,753,666,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | — | 
                                                18,948,138,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                19,102,068,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                12,192,960,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                6,051,757,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                6,366,526,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net assets per share | — | 
                                                1,645.86
                                                
                                             | — | 
                                                1,499.58
                                                
                                             | 
                                                842.95
                                                
                                             | — | — | 
                                                397.25
                                                
                                             | 
                                                394.10
                                                
                                             | — | 
| Dividend paid per share | 
                                                200
                                                
                                             | — | 
                                                250
                                                
                                             | — | — | 
                                                155
                                                
                                             | 
                                                10
                                                
                                             | — | — | 
                                                29
                                                
                                             | 
| Interim dividend paid per share | 
                                                60
                                                
                                             | — | 
                                                60
                                                
                                             | — | — | 
                                                50
                                                
                                             |  | — | — |  | 
| Basic earnings (loss) per share | 
                                                396.27
                                                
                                             | — | 
                                                822.94
                                                
                                             | — | — | 
                                                505.73
                                                
                                             | 
                                                32.16
                                                
                                             | — | — | 
                                                91.80
                                                
                                             | 
| Diluted earnings per share |  | — |  | — | — |  |  | — | — |  | 
| Equity-to-asset ratio | — | 
                                                0.827
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.748
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.658
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.625
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.590
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Rate of return on equity | 
                                                0.252
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.703
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.816
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.081
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.253
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Price-earnings ratio | 
                                                7.9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                4.6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                4.7
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                40.0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                30.6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Payout ratio | 
                                                0.505
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.304
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.306
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.311
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.316
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Net cash provided by (used in) operating activities | 
                                                3,991,831,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                6,172,506,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                5,596,506,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                295,417,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                745,001,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) investing activities | 
                                                -270,448,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,553,587,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -159,737,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -97,317,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -762,284,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) financing activities | 
                                                -2,381,004,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -1,570,737,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -1,164,585,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -361,099,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -814,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Cash and cash equivalents | — | 
                                                8,716,464,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                7,375,146,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                4,326,563,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                54,312,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                217,242,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Number of employees | — | 
                                                180
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                175
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                173
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                175
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                175
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Average number of temporary employees | — | 
                                                45
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                41
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                46
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                49
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                51
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Total shareholder return | — | 
                                                2.091
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                2.317
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1.410
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.732
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1.569
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Total return on share price index | — | 
                                                1.789
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                1.395
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1.430
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                1.268
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1.181
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |