Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current income tax expense:
Federal									$ 63,035	$ 120,968	$ 63,642
State									64,917	72,837	48,558
Foreign									3,513	1,815	1,345
Total current income tax expense									131,465	195,620	113,545
Deferred income tax (benefit) expense:
Federal									(11,870)	40,057	25,296
State									(4,600)	(6,201)	1,883
Foreign									0	0	(213)
Total deferred income tax (benefit) expense									(16,470)	33,856	26,966
Income tax expense	$ 32,037	$ 33,563	$ 24,643	$ 24,752	$ 89,229	$ 42,624	$ 39,355	$ 58,268	$ 114,995	$ 229,476	$ 140,511