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Operating Segments - Additional Information (Detail)
12 Months Ended
Mar. 31, 2018
Segment
Customer
Mar. 31, 2017
Mar. 31, 2016
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    
Percentage of revenue from top customer   9.00% 10.90%
Percentage of trade receivables of top customer   7.10% 10.00%