Key Financial Data Of Group
| Concept | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | 2023-04-01 to 2024-03-31 | As at 2023-03-31 | 2022-04-01 to 2023-03-31 | 2021-04-01 to 2022-03-31 | As at 2022-03-31 | 2020-04-01 to 2021-03-31 | As at 2021-03-31 | As at 2020-03-31 | 2019-04-01 to 2020-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Key financial data of group | ||||||||||||||
| Business results of group | ||||||||||||||
| Net sales | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                13,237,395,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                13,065,401,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Revenue | — | — | — | — | — | 
                                                10,143,154,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                9,960,242,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                9,676,056,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Ordinary profit (loss) | — | — | — | — | — | 
                                                795,796,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                621,019,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                754,246,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,460,018,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,204,513,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net assets | — | 
                                                7,419,776,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                7,292,198,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                7,490,993,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                6,031,800,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,173,580,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | — | 
                                                13,950,101,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                13,762,244,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                13,512,765,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                12,778,823,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                12,065,055,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net assets per share | — | 
                                                1,571.93
                                                
                                             | — | — | — | — | 
                                                1,544.89
                                                
                                             | — | — | 
                                                1,587.01
                                                
                                             | — | 
                                                1,551.69
                                                
                                             | 
                                                1,330.91
                                                
                                             | — | 
| Basic earnings (loss) per share | — | — | — | — | — | 
                                                85.15
                                                
                                             | — | 
                                                17.44
                                                
                                             | 
                                                83.46
                                                
                                             | — | 
                                                253.21
                                                
                                             | — | — | 
                                                207.65
                                                
                                             | 
| Diluted earnings per share | — | — | — | — | — |  | — |  |  | — |  | — | — |  | 
| Equity-to-asset ratio | — | 
                                                0.532
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
                                                0.530
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.554
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.472
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.429
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Rate of return on equity | — | — | — | — | — | 
                                                0.055
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.011
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.058
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.176
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.166
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Price-earnings ratio | — | — | — | — | — | 
                                                17.80
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                76.26
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                15.11
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Net cash provided by (used in) operating activities | — | — | — | — | — | 
                                                1,191,479,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,339,174,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                515,072,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,434,323,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                1,318,109,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) investing activities | — | — | — | — | — | 
                                                -523,035,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -2,010,311,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -2,206,702,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -653,233,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -805,733,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net cash provided by (used in) financing activities | — | — | — | — | — | 
                                                -286,137,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -285,944,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,118,868,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -178,796,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -236,794,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Cash and cash equivalents | — | 
                                                4,099,395,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                3,717,088,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                4,674,169,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                5,246,931,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,644,638,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Number of employees | 
                                                26
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                447
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                21
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                221
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                179
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                457
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                456
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                445
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                434
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Average number of temporary employees | 
                                                0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                87
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                87
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                102
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                92
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                96
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                122
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — |