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 | 
                                                106
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                451
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,133
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,237
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,665
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,027
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                121
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,201
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,104
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,093
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,138
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,050
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,089
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,072
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,883
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | 
                                                42.0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | 
                                                16.8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | 
                                                6,789,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — |