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Summary of significant accounting policies - Intangible assets (Details)
 12 Months Ended
Dec. 31, 2020
Internal-use software technology | Minimum  
Disclosure of detailed information about intangible assets [line items]  
Useful life 5 years
Internal-use software technology | Maximum  
Disclosure of detailed information about intangible assets [line items]  
Useful life 10 years
Brands and trademarks  
Disclosure of detailed information about intangible assets [line items]  
Useful life 3 years
Customer lists | Minimum  
Disclosure of detailed information about intangible assets [line items]  
Useful life 5 years
Customer lists | Maximum  
Disclosure of detailed information about intangible assets [line items]  
Useful life 10 years