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 | 
                                                304
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                7,995
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                7,546
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                273
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                299
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                7,830
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,103
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                302
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                166
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,030
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                47
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,763
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,754
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                42
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                40
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,905
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,012
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                51
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                25
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,014
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | 
                                                38.3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | 
                                                12.0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average annual salary | 
                                                7,313,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — |