Income Taxes (Income Tax Expense (Benefit)) (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 taxes:
Federal									$ 44,266	$ 54,977	$ 98,272
State									18,349	12,852	20,041
Foreign									(872)	1,243	(10)
Total current income taxes									61,743	69,072	118,303
Deferred income taxes:
Federal									40,500	51,668	4,464
State									11,705	10,403	(14)
Foreign									3,019	1,172	2,226
Total deferred income taxes									55,224	63,243	6,676
Total income tax expense	$ 28,005	$ 30,866	$ 32,011	$ 26,085	$ 27,004	$ 38,622	$ 37,049	$ 29,640	$ 116,967	$ 132,315	$ 124,979