Employees
| 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 | 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 | As at 2023-03-31 | As at 2023-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2020-03-31 | As at 2020-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Employees | ||||||||||||||||||
| Information about reporting company | ||||||||||||||||||
| Information about employees of reporting company | ||||||||||||||||||
| Number of employees | 
                                                142
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                627
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                23
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                305
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                485
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                356
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                682
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                55
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                51
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                282
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                627
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                335
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                322
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                599
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                572
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                318
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                316
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                583
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                102
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                178
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                11
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                64
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                76
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                75
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                191
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                13
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                11
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                53
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                167
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                76
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                74
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                159
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                148
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                69
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                67
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                148
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | — | — | 
                                                40.4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | — | 
                                                12.6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | — | 
                                                5,139,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — |