Employees
| Concept | 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 | 
                                                1,687
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,901
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,830
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,645
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,578
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,727
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,644
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,531
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,507
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,617
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                320
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                320
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                313
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                313
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                328
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                328
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                337
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                336
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                316
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                316
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | 
                                                41.9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | 
                                                16.9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average annual salary | 
                                                9,052,522
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — |