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Goodwill - Carrying Value of Goodwill Allocated to Cash Generating Units ("CGU") (Detail) - USD ($)
$ in Thousands
Mar. 31, 2019
Apr. 01, 2018
Mar. 31, 2018
Mar. 31, 2017
Disclosure of information for cash-generating units [line items]        
Goodwill $ 130,811 $ 135,186 $ 135,186  
WNS global BPM [member]        
Disclosure of information for cash-generating units [line items]        
Goodwill 3,846   3,815  
South Africa [member]        
Disclosure of information for cash-generating units [line items]        
Goodwill 4,557   5,581  
Research and analytics [member]        
Disclosure of information for cash-generating units [line items]        
Goodwill 46,087   48,901  
Technology services [member]        
Disclosure of information for cash-generating units [line items]        
Goodwill 3,382   3,632  
WNS Auto Claims BPM [member]        
Disclosure of information for cash-generating units [line items]        
Goodwill 4,315   4,633 $ 4,130
Denali Sourcing Services Inc. [member]        
Disclosure of information for cash-generating units [line items]        
Goodwill 29,542   29,542  
HealthHelp [member]        
Disclosure of information for cash-generating units [line items]        
Goodwill $ 39,082   $ 39,082