Income Taxes (Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current income taxes:
Federal									$ 98,272	$ 62,584	$ 75,945
State									20,041	9,417	10,397
Foreign									(10)	(39)	4,566
Total current income taxes									118,303	71,962	90,908
Deferred income taxes:
Federal									4,464	15,550	466
State									(14)	5,962	6,113
Foreign									2,226	1,542	(2,454)
Total deferred income taxes									6,676	23,054	4,125
Total income tax expense	$ 33,724	$ 31,939	$ 29,930	$ 29,386	$ 20,896	$ 23,842	$ 26,295	$ 23,983	$ 124,979	$ 95,016	$ 95,033