XML 186 R164.htm IDEA: XBRL DOCUMENT v3.21.1
Summary of significant accounting policies - Narrative (Details)
 12 Months Ended
Dec. 31, 2020
contract
Disclosure of detailed information about intangible assets [line items]  
Number of power agreements 2
Expiration Date 2042  
Disclosure of detailed information about intangible assets [line items]  
Power agreement terms 15 years
Expiration date 2024  
Disclosure of detailed information about intangible assets [line items]  
Power agreement terms 15 years
Expiration date 2025  
Disclosure of detailed information about intangible assets [line items]  
Power agreement terms 15 years
Trademarks | Bottom of range  
Disclosure of detailed information about intangible assets [line items]  
Useful lives of intangible assets 10 years
Trademarks | Top of range  
Disclosure of detailed information about intangible assets [line items]  
Useful lives of intangible assets 20 years
Software | Bottom of range  
Disclosure of detailed information about intangible assets [line items]  
Useful lives of intangible assets 3 years
Software | Top of range  
Disclosure of detailed information about intangible assets [line items]  
Useful lives of intangible assets 5 years