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 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 | 
                                                84
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                320
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                404
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                84
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                451
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                320
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                47
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                454
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                409
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                408
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                454
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                454
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                410
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                406
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                454
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                145
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                525
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                670
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                145
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                713
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                525
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                43
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                724
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                686
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                695
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                736
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                726
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                683
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                713
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                758
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | 
                                                43.3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | 
                                                18.3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | 
                                                5,190,296
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — |