Income Taxes (Reconciliation of Provision for Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Provision for Income Taxes
Federal income tax expense at statutory tax rate	$ 53,892	$ 52,190	$ 25,844
State income taxes, net of federal tax benefit	7,753	4,614	3,685
Impact of federal tax law change	(53,348)
Officers' compensation	2,622	3,807	2,900
Domestic production activities deduction	(2,668)	(4,018)	(1,499)
Noncontrolling interest	(2,137)
Reversal of taxes payable due to statue expiration	(4,337)
Other	(2,346)	(3,300)	(2,383)
Total provision	$ (569)	$ 53,293	$ 28,547
Reconciliation of Effective Income Tax Rate
Federal income tax expense at statutory tax rate (in hundredths)	35.00%	35.00%	35.00%
State income taxes, net of federal tax benefit (in hundredths)	5.00%	3.10%	5.00%
Impact of federal tax law change (in hundredths)	(34.60%)
Officers' compensation (in hundredths)	1.70%	2.60%	3.90%
Domestic production activities deduction (in hundredths)	(1.70%)	(2.70%)	(2.00%)
Noncontrolling interest (in hundredths)	(1.40%)
Reversal of taxes payable due to statue expiration (in hundredths)	(2.80%)
Other (in hundredths)	(1.60%)	(2.30%)	(3.20%)
Total (benefit) provision (in hundredths)	(0.40%)	35.70%	38.70%