Income Taxes - Effective Income Tax Rates (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense (benefit) based on the U.S. statutory tax rate	$ 42,735	$ 9,031		$ (98,868)
Revaluation of deferred tax (U.S. tax reform)	0	0		118,004
Alberta tax rate reduction and tax impact of deemed repatriation of foreign invested earnings (U.S. tax reform)	(17,019)	(135,700)		156,000
Deferred tax effect on Canadian earnings no longer indefinitely invested	0	0		65,000
Foreign income (loss) subject to foreign tax rates different than the U.S.statutory rate	(1,122)	5,822		2,032
State income taxes, net of federal benefit	4,060	2,607		2,438
U.S. tax benefit on certain foreign upstream investments	(14,975)	(14,702)		(32,926)
Increase in deferred tax asset valuation allowance related to other foreign exploration expenditures	10,927	3,283		18,601
Tax effect on income attributable to noncontrolling interest	(21,750)	(1,753)		0
Other, net	11,827	5,276		39,850
Total income tax expense (benefit)	$ 14,683	$ (126,136)	[1]	$ 270,131	[1]

[1] ¹ Reclassified to conform with current presentation (see Notes C and E). 2017 revenue is presented net of $58.9 million of transportation, gathering and processing costs as historically shown prior to the adoption of ASC 606 on January 1, 2018. See Notes to Consolidated Financial Statements, page 58.