Income Taxes (Components of Income Tax Expense) (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
Federal									$ 6,163	$ 5,140	$ 5,460
State									4,424	150	(2,630)
Total current income tax expense									10,587	5,290	2,830
Deferred
Federal									108,877	92,360	78,870
State									13,027	9,660	11,545
Total deferred income tax expense									121,904	102,020	90,415
Total income tax expense	$ 32,342	$ 36,058	$ 32,242	$ 31,849	$ 25,756	$ 25,868	$ 27,078	$ 28,608	132,491	107,310	93,245
Share-based compensation tax benefit (deficiency)									$ 1,656	$ (3,168)	$ 317