Income Taxes (Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current income taxes:
Federal									$ 62,584	$ 75,945	$ 67,449
State									9,417	10,397	16,046
Foreign									(39)	4,566	2,196
Total current income taxes									71,962	90,908	85,691
Deferred income taxes:
Federal									15,550	466	1,813
State									5,962	6,113	(114)
Foreign									1,542	(2,454)	(160)
Total deferred income taxes									23,054	4,125	1,539
Total income tax expense	$ 20,896	$ 23,842	$ 26,295	$ 23,983	$ 23,669	$ 25,034	$ 24,490	$ 21,840	$ 95,016	$ 95,033	$ 87,230