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 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 | 
                                                398
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                555
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                494
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                356
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                61
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                42
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                559
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                401
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                406
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                579
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                585
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                412
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                410
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                586
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
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                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | 
                                                45.7
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | 
                                                22.1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average annual salary | 
                                                5,241,000
                                                
                                                    
                                                        JPY
                                                    
                                                
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