XML 112 R92.htm IDEA: XBRL DOCUMENT v3.20.4
Other long-term liabilities - Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Opening balance $ 53,879 $ 43,291
Obligation assumed from business acquisition and constructed projects 20,420 3,226
Retirement activities (1,724) (443)
Accretion 2,674 2,148
Change in cash flow estimates 4,719 5,657
Closing balance $ 79,968 $ 53,879