Employees
| Concept | As at 2020-03-31 | As at 2020-03-31 | As at 2020-03-31 | As at 2020-03-31 | As at 2020-03-31 | As at 2020-03-31 | As at 2020-03-31 | As at 2019-03-31 | As at 2019-03-31 | As at 2018-03-31 | As at 2018-03-31 | As at 2017-03-31 | As at 2017-03-31 | As at 2016-03-31 | As at 2016-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Employees | |||||||||||||||
| Information about group | |||||||||||||||
| Number of employees of group | |||||||||||||||
| Number of employees | 
                                                353
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                576
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,088
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                690
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                576
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                376
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                669
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,082
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                574
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                553
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,060
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                557
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,928
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,844
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                545
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             |