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Certain risks and concentration - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2020
USD ($)
customer
Dec. 31, 2019
USD ($)
Dec. 31, 2018
Concentration Risk [Line Items]      
Maximum foreign ownership in internet information provider or other value-added telecommunication service provider's business allowed under PRC laws and regulations 50.00%    
Retained earnings and distributable reserves $ (181,095,000) $ (166,973,000)  
Number of top customers accounted for net revenues | customer 10    
Intercompany balance included in accounts payable $ 30,439,000 21,297,000  
Accrued Liabilities and Other Liabilities, Inter-companies Balance 152,611,000 152,904,000  
Amount of Restricted Net Assets for Consolidated and Unconsolidated Subsidiaries 168,493,000    
Variable Interest Entity, Primary Beneficiary [Member]      
Concentration Risk [Line Items]      
Accounts payable, consolidated variable interest entities and VIE's subsidiaries without recourse 20,588,000 23,865,000  
Accrued liabilities and other payables, consolidated variable interest entities and VIE's subsidiaries without recourse $ 33,361,000 $ 38,502,000  
Shenzhen Xunlei      
Concentration Risk [Line Items]      
Term of operating contract 10 years    
Sales Revenue, Net [Member] | Customer concentration risk [Member]      
Concentration Risk [Line Items]      
Percentage of net revenues accounted from customers 38.00% 31.00% 23.00%