Income Taxes (Reconciliation of Provision for Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Provision for Income Taxes
Federal income expense at statutory tax rate	$ 25,844	$ 65,603	$ 48,865
State income taxes, net of federal tax benefit	1,250	10,367	6,236
Officers' compensation	2,900	3,657	1,732
Domestic Production Activities Deduction	(1,499)	(5,170)	(3,641)
Impact of state tax rate changes on deferreds	2,435	3,245
Other	(2,383)	1,800	(873)
Total provision	$ 28,547	$ 79,502	$ 52,319
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)	1.70%	5.50%	4.50%
Officers' compensation (in hundredths)	3.90%	2.00%	1.20%
Domestic Production Activities Deduction (in hundredths)	(2.00%)	(2.80%)	(2.60%)
Impact of state tax rate changes on deferreds (in hundredths)	3.30%	1.70%
Other (in hundredths)	(3.20%)	1.00%	(0.60%)
Total (benefit) provision (in hundredths)	38.70%	42.40%	37.50%