Income Taxes - Effective Income Tax Rates (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax expense (benefit) based on the U.S. statutory tax rate	$ (325,299)	$ 42,735	$ 9,031
Alberta tax rate reduction and tax impact of deemed repatriation of foreign invested earnings (U.S. tax reform)	0	(17,019)	(135,700)
Foreign income (loss) subject to foreign tax rates different than the U.S.statutory rate	(3,791)	(1,122)	5,822
State income taxes, net of federal benefit	(6,646)	4,060	2,607
U.S. tax benefit on certain foreign upstream investments	0	(14,975)	(14,702)
Increase in deferred tax asset valuation allowance related to other foreign exploration expenditures	7,707	10,927	3,283
Tax effect on income attributable to noncontrolling interest	23,712	(21,750)	(1,753)
Other, net	10,576	11,827	5,276
Total income tax expense (benefit)	$ (293,741)	$ 14,683	$ (126,136)