Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statutory federal tax rate	21.00%	35.00%	35.00%
Income Tax Expense (Benefit)	$ 363,969	$ 129,439	$ 204,127
Income Tax Expense (Benefit) Due to Tax Reform		(180,600)
Deferred Tax Assets, Valuation Allowance	21,788	20,714
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	6,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	(1,300)
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	2,400
Minimum
Income Tax Examination, Estimate of Possible Loss	0
Maximum
Income Tax Examination, Estimate of Possible Loss	5,300
Domestic Tax Authority [Member]
Income Tax Expense (Benefit) Due to Tax Reform		(182,500)
Operating Loss Carryforwards	102,800
Foreign Tax Authority [Member]
Income Tax Expense (Benefit) Due to Tax Reform		1,900
Parent Company [Member]
Income Tax Expense (Benefit)	153,528	(69,961)	69,454
Guarantors
Income Tax Expense (Benefit)	239,198	226,327	180,990
Combined Non-Guarantors
Income Tax Expense (Benefit)	$ 647	$ 5,266	$ (15,825)