Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Taxes
Income tax provision at statutory rate	$ (10,105)	$ 13,216	$ (15,794)	$ 28,506
Percentage depletion allowance	(11,768)	(3,457)	(5,600)	(7,764)
State taxes, net of effect of federal taxes	(1,584)	831	(1,502)	1,843
Change in valuation allowance	19,531	(11,292)	20,381	(23,805)
Current expense associated with uncertain tax positions	5,132	844	3,101	1,437
AMT sequestration refund			(1,171)
Other, net		(51)	0	(56)
Provision for (benefit from) income taxes	1,206	$ 91	(585)	$ 161
Refund, AMT credits	37,400		37,400
Tax reserve for portion of refund subject to audit	$ 13,300		$ 13,300
Percentage of the total income tax refund amount subject to audit	40.00%

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The amount of reserve established for portion of refund subject to audit risk.

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The amount of the additional liability or refund received or expected based on a final settlement with a taxing authority.

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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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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 income tax settlements. Including, but not limited to, domestic tax settlement, foreign tax settlement, state and local tax settlement, and other tax settlements.

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