Employees
| Concept | 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 | 
                                                597
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                719
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                875
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,020
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,039
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                119
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                151
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                180
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                183
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                172
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | 
                                                33.2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
| Average length of service (Years) | 
                                                10.9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
| Average annual salary | 
                                                3,788,389
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — |