Income Taxes (Reconciliation of Provision for Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Provision for Income Taxes
Federal income expense at statutory tax rate	$ 52,190	$ 25,844	$ 65,603
State income taxes, net of federal tax benefit	5,972	1,250	10,367
Officers' compensation	3,807	2,900	3,657
Domestic Production Activities Deduction	(4,018)	(1,499)	(5,170)
Impact of state tax rate changes on deferred taxes	(1,358)	2,435	3,245
Other	(3,300)	(2,383)	1,800
Total provision	$ 53,293	$ 28,547	$ 79,502
Reconciliation of Effective Income Tax Rate
Federal income expense at statutory tax rate (in hundredths)	35.00%	35.00%	35.00%
State income taxes, net of federal tax benefit (in hundredths)	4.00%	1.70%	5.50%
Officers' compensation (in hundredths)	2.60%	3.90%	2.00%
Domestic Production Activities Deduction (in hundredths)	(2.70%)	(2.00%)	(2.80%)
Impact of state tax rate changes on deferred taxes (in hundredths)	(0.90%)	3.30%	1.70%
Other (in hundredths)	(2.30%)	(3.20%)
Other (in hundredths)			1.00%
Total (benefit) provision (in hundredths)	35.70%	38.70%	42.40%