Income Taxes (Schedule of Effective Income Tax Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax at statutory rate	$ 50,595	$ 44,611	$ 70,406
Change in federal income tax rate	(110,508)	0	0
State income taxes, net of federal tax benefits	4,943	3,032	6,627
Non-deductible meals and entertainment	1,495	1,549	1,687
Income tax credits	(1,780)	(1,900)	(1,700)
Equity compensation	(820)	0	0
Other, net	(2,257)	1,039	427
Total income tax expense (benefit)	$ (58,332)	$ 48,331	$ 77,447