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Goodwill - Summary of Movement in Goodwill by Reportable Segment (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Mar. 31, 2017
Disclosure of reconciliation of changes in goodwill [line items]      
Beginning balance $ 135,186    
Impairment of goodwill recognized during the year 0 $ 0 $ 21,673
Ending balance 130,811 135,186  
Accumulated impairment [member]      
Disclosure of reconciliation of changes in goodwill [line items]      
Beginning balance (24,314) (21,673)  
Impairment of goodwill recognized during the year 0 0  
Foreign currency translation 1,672 (2,641)  
Ending balance (22,642) (24,314) (21,673)
Accumulated impairment [member] | WNS global BPM [member]      
Disclosure of reconciliation of changes in goodwill [line items]      
Impairment of goodwill recognized during the year 0 0  
Accumulated impairment [member] | WNS Auto Claims BPM [member]      
Disclosure of reconciliation of changes in goodwill [line items]      
Beginning balance (24,314) (21,673)  
Impairment of goodwill recognized during the year 0 0  
Foreign currency translation 1,672 (2,641)  
Ending balance (22,642) (24,314) (21,673)
Gross carrying value [member]      
Disclosure of reconciliation of changes in goodwill [line items]      
Beginning balance 159,500 155,681  
Goodwill arising on acquisitions 203 (92)  
Foreign currency translation (6,250) 3,911  
Ending balance 153,453 159,500 155,681
Gross carrying value [member] | WNS global BPM [member]      
Disclosure of reconciliation of changes in goodwill [line items]      
Beginning balance 130,553 129,878  
Goodwill arising on acquisitions 203 (92)  
Foreign currency translation (4,260) 767  
Ending balance 126,496 130,553 129,878
Gross carrying value [member] | WNS Auto Claims BPM [member]      
Disclosure of reconciliation of changes in goodwill [line items]      
Beginning balance 28,947 25,803  
Foreign currency translation (1,990) 3,144  
Ending balance $ 26,957 $ 28,947 $ 25,803