Employees
| Concept | 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 2022-03-31 | As at 2021-03-31 | As at 2020-03-31 | 
|---|---|---|---|---|---|---|---|---|
| Employees | ||||||||
| Information about reporting company | ||||||||
| Information about employees of reporting company | ||||||||
| Number of employees | 
                                                241
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                564
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                887
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                82
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                849
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                790
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                728
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                688
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | 
                                                36.8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | 
| Average length of service (Years) | — | — | 
                                                10.1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | 
| Average annual salary | — | — | 
                                                6,638,243
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — |