Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Income tax provision and earnings for continuing operations

		2017		2016		2015
Current:
	Federal	$	29,537	$	1,494	$	1,571
	State		(67)		(252)		535
	Total current		29,470		1,242		2,106
Deferred:
	Federal		—		915		(76,300)
	State		—		56		(3,186)
	Total deferred		—		971		(79,486)
Total income tax benefit (expense)		$	29,470	$	2,213	$	(77,380)

Schedule of tax effects of temporary differences that result in deferred tax assets and deferred tax liabilities for continuing operations

		2017		2016
Deferred income tax assets:
	Accrued expense and liabilities	$	17,530	$	26,746
	Pension and other postretirement benefits		5,898		8,621
	Accrued reclamation and mine closure costs		22,229		34,326
	Contract rights		38,793		69,352
	Debt restructuring		12,762		25,183
	Mark-to-market gain (loss)		52		(191)
	AMT Credit carryforward		—		31,625
	Net operating loss carryforward		55,160		54,764
	Other		866		7,606
Total deferred income tax assets			153,290		258,032
Less valuation allowance			(52,010)		(99,638)
Net deferred income tax asset			101,280		158,394
Deferred income tax liabilities:
	Property, plant and equipment		(33,420)		(37,954)
	Inventories		(11,521)		(17,435)
	Mineral rights		(44,878)		(78,819)
	Throughput payments		(3,604)		(12,928)
	Other		(7,857)		(11,258)
Total deferred income tax liabilities			(101,280)		(158,394)
Net deferred income tax assets (liabilities)		$	—	$	—

Schedule of reconciliation of effective tax rate of the Company with U.S. federal statutory income tax rate

	2017		2016		2015
United States federal statutory income tax rate	35.0	%	35.0	%	35.0	%
State income taxes, net of federal tax benefit	2.2		1.2		1.3
Percentage depletion	12.9		(25.0)		5.7
Change in valuation allowance	48.5		(32.4)		(86.9)
AMT credit monetization - valuation allowance release	85.6		—		—
Other non-deductible expenses	(2.1)		1.7		(0.5)
Stock compensation	(5.8)		12.1		(1.5)
Non-deductible goodwill impairment	—		—		(9.1)
Deferred tax adjustments	(9.0)		(4.7)		(4.7)
Impact of US Tax Reform	(87.3)		—		—
Other	—		0.4		0.6
Effective tax rate	80.0	%	(11.7)	%	(60.1)	%