Income Taxes (Effective Income Tax Rates) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Line Items]
Income tax expense (benefit) based on the U.S. statutory tax rate	$ 90,791	$ 25,131	$ (172,590)
Revaluation of deferred tax (U.S. tax reform)		118,004
Tax impact of deemed repatriation of foreign ivnested earnings (U.S. tax reform)	(135,700)	156,000
Deferred tax effect on Canadian earnings no longer indefinitely invested		65,000
Foreign income (loss) subject to foreign tax rates different than the U.S. statutory rate	72,007	12,658	8,582
State income taxes, net of federal benefit	2,607	2,438	9,090
U.S. tax benefit on certain foreign upstream investments	(14,702)	(32,926)	(21,336)
Increase in deferred tax asset valuation allowance related to other foreign exploration expenditures	3,283	18,601	25,734
Other, net	$ (8,956)	$ 17,832	18,741
Canada [Member]
Income Tax Disclosure [Line Items]
Tax effects on sale of assets			(89,473)
Malaysia [Member]
Income Tax Disclosure [Line Items]
Tax effects on sale of assets			$ 2,080