Income Taxes (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended							12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current income tax (benefit) provision
State income tax									$ (46)
Federal alternative minimum tax										(1,411)
Net current income tax benefit									(46)	(1,411)
Deferred income tax provision (benefit)
Federal tax expense at statutory rate (34%)								(11,767)	(5,319)	3,365
Statutory depletion carryforward									231	(157)
State income tax								(819)	(435)
Change in state rate applied										275
Nondeductible expense								(122)	48	38
Permanent differences								1,018
Federal alternative minimum tax										1,411
Change in valuation allowance								10,260
Net deferred income tax (benefit) provision								(1,430)	(5,475)	4,932
Total income tax (benefit) provision	$ (188)	$ (593)	$ (3,713)	$ 3,064	$ 1,430	$ (46)	$ (6,906)	$ (1,430)	$ (5,521)	$ 3,521