Income Taxes Income Taxes (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income tax expense (benefit) at statutory rate of 35%	$ 23,999	$ (13,052)	$ 19,989
Tax depletion in excess of basis	(729)	(518)	(581)
Revision of previous tax estimates	(155)	373	700
State income taxes, net of federal tax effect	1,008	76	1,513
Other	564	693	387
Income tax expense (benefit)	24,687us-gaap_IncomeTaxExpenseBenefit	(12,428)us-gaap_IncomeTaxExpenseBenefit	22,008us-gaap_IncomeTaxExpenseBenefit
Current	227us-gaap_CurrentIncomeTaxExpenseBenefit	1,614us-gaap_CurrentIncomeTaxExpenseBenefit	0us-gaap_CurrentIncomeTaxExpenseBenefit
Deferred	24,460us-gaap_DeferredIncomeTaxExpenseBenefit	(14,042)us-gaap_DeferredIncomeTaxExpenseBenefit	22,008us-gaap_DeferredIncomeTaxExpenseBenefit
Income tax expense (benefit)	$ 24,687us-gaap_IncomeTaxExpenseBenefit	$ (12,428)us-gaap_IncomeTaxExpenseBenefit	$ 22,008us-gaap_IncomeTaxExpenseBenefit
Statutory tax rate	35.00%	35.00%	35.00%

Income Tax Reconciliation, Income Tax Expense (Benefit), Revision of Tax Estimates

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Amount of current income tax expense (benefit) pertaining to taxable income (loss) from continuing operations.

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Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to nondeductible depletion.

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