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Goodwill - Key Assumptions Used in Performing Impairment Test, by each CGU (Detail)
Mar. 31, 2019
Mar. 31, 2017
WNS global BPM [member]    
Disclosure of information for cash-generating units [line items]    
Discount rate 16.50%  
Perpetual growth rate 3.00%  
South Africa [member]    
Disclosure of information for cash-generating units [line items]    
Discount rate 17.00%  
Perpetual growth rate 3.00%  
Denali Sourcing Services Inc. [member]    
Disclosure of information for cash-generating units [line items]    
Discount rate 13.20%  
Perpetual growth rate 2.50%  
Research and analytics [member]    
Disclosure of information for cash-generating units [line items]    
Discount rate 16.50%  
Perpetual growth rate 3.00%  
HealthHelp [member]    
Disclosure of information for cash-generating units [line items]    
Discount rate 13.20%  
Perpetual growth rate 2.50%  
Technology services [member]    
Disclosure of information for cash-generating units [line items]    
Discount rate 15.50%  
Perpetual growth rate 2.00%  
WNS Auto Claims BPM [member]    
Disclosure of information for cash-generating units [line items]    
Discount rate 15.50% 13.00%
Perpetual growth rate 2.00%