Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income tax provision at statutory rate	$ 13,216	$ 8,387	$ 28,506	$ 20,870
Percentage depletion allowance	(3,457)	(2,488)	(7,764)	(7,095)
State taxes, net of effect of federal taxes	831	583	1,843	1,337
Change in valuation allowance	(11,292)	(7,317)	(23,805)	(17,956)
Current expense associated with uncertain tax positions	844	792	1,437	2,181
Other, net	(51)	(3,323)	(56)	(3,247)
Provision for (benefit from) income taxes	$ 91	$ (3,366)	$ 161	$ (3,910)

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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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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 increase (decrease) in the valuation allowance for deferred tax assets.

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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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