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Goodwill - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Disclosure of reconciliation of changes in goodwill [line items]    
Estimated cash flows period P5Y  
Impairment charge $ 0 $ (21,673)
Goodwill $ 135,186 134,008
WNS Auto Claims BPM [member]    
Disclosure of reconciliation of changes in goodwill [line items]    
Impairment charge   $ 21,673
Discount rate 14.00% 13.00%
Growth rate 2.00%  
Recoverable amount of cash generating units   $ 37,836
Goodwill $ 4,633 4,130
Disposal cost   $ 656
WNS Auto Claims BPM [member] | Annual Growth Rate [member]    
Disclosure of reconciliation of changes in goodwill [line items]    
Growth rate   2.50%
WNS Auto Claims BPM [member] | Perpetual Growth Rate [member]    
Disclosure of reconciliation of changes in goodwill [line items]    
Growth rate   2.00%