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Related Party - List of the Company's Subsidiaries (Detail) - Subsidiary
12 Months Ended
Mar. 15, 2017
Jun. 14, 2016
Mar. 31, 2019
Mar. 31, 2018
WNS Global Services (UK) Limited [member]        
Disclosure of transactions between related parties [Line Items]        
Proportion of ownership interest     71.70%  
WNS Global Services SA (Pty) Limited [Member] | WNS B-BBEE Staff Share Trust [Member]        
Disclosure of transactions between related parties [Line Items]        
Proportion of ownership interest     10.00%  
WNS Global Services SA (Pty) Limited [Member] | WNS Global Services (UK) Limited [member]        
Disclosure of transactions between related parties [Line Items]        
Proportion of ownership interest     90.00%  
WNS Global Services Private Limited [member] | WNS Customer Solutions (Singapore) Private Limited [member]        
Disclosure of transactions between related parties [Line Items]        
Proportion of ownership interest     20.00%  
WNS Global Services Private Limited [member] | WNS Global Services (UK) Limited [member]        
Disclosure of transactions between related parties [Line Items]        
Proportion of ownership interest     28.30%  
WNS Global Services Private Limited [member] | WNS (Mauritius) Limited [member]        
Disclosure of transactions between related parties [Line Items]        
Proportion of ownership interest     80.00%  
MTS HealthHelp Inc. [member] | HealthHelp Holdings LLC [member]        
Disclosure of transactions between related parties [Line Items]        
Proportion of ownership interest 63.70%      
WNS North America Inc. [member] | HealthHelp Holdings LLC [member]        
Disclosure of transactions between related parties [Line Items]        
Proportion of ownership interest 36.30%      
Value Edge Research Services Private Limited [member]        
Disclosure of transactions between related parties [Line Items]        
Number of subsidiaries acquired   3    
WNS Assistance Limited [member] | WNS Legal Assistance LLP [member]        
Disclosure of transactions between related parties [Line Items]        
Proportion of ownership interest     98.75%  
WNS Assistance (Legal) Limited [member] | WNS Legal Assistance LLP [member]        
Disclosure of transactions between related parties [Line Items]        
Proportion of ownership interest     1.25%  
WNS Legal Assistance LLP [member] | Prettys Solicitors LLP [member]        
Disclosure of transactions between related parties [Line Items]        
Proportion of ownership interest       20.00%