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Operating Segments - Additional Information (Detail)
12 Months Ended
Mar. 31, 2019
Customer
Segment
Mar. 31, 2018
Customer
Mar. 31, 2017
Disclosure of operating segments [Line Items]      
Number of reportable segment | Segment 2    
WNS Global BPM segment [member]      
Disclosure of operating segments [Line Items]      
Number of clients individually accounted for more than 10% of total revenue | Customer 0 0  
Percentage of revenue from top customer     9.00%
Percentage of trade receivables of top customer     7.10%