Income Taxes Income Taxes (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income tax expense (benefit) at statutory rate of 35%	$ 19,989	$ 50,921	$ 20,150
Tax depletion in excess of basis	(581)	(425)	(490)
Revision of previous tax estimates	700	217	8
State income taxes, net of federal tax effect	1,513	1,310	884
Other	387	119	82
Income tax expense	22,008	52,142	20,634
Current	0	(408)	375
Deferred	22,008	52,550	20,259
Income tax expense	$ 22,008	$ 52,142	$ 20,634
Statutory rate	35.00%	35.00%	35.00%