Employees
| Concept | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | 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 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Employees | ||||||||||||||||
| Information about reporting company | ||||||||||||||||
| Information about employees of reporting company | ||||||||||||||||
| Number of employees | 
                                                265
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,594
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                185
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                176
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,243
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,802
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,876
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                97
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,865
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,213
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,186
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,857
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,827
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,125
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,059
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,806
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | — | — | — | 
                                                41.4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | — | — | 
                                                17.2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | — | — | 
                                                9,192,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — |