Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Summary of Income Tax (Expense) Benefit

	Years Ended December 31,
	2015			2014			2013
Current:
Federal	$	(170	)	$	(34,790	)	$	(20,819	)
State	1,448			(4,835		)	(1,831		)
	$	1,278		$	(39,625	)	$	(22,650	)
Deferred:
Federal	7,439			(308		)	1,453
State	3,034			2,750			436
	$	10,473		$	2,442		$	1,889
Income tax benefit (expense)	$	11,751		$	(37,183	)	$	(20,761	)

Summary of Tax Effects on Deferred Tax Assets and Liabilities

	At December 31,
	2015			2014
Gross deferred tax assets:
State tax credits and net operating loss carry forward	$	39,280		$	25,042
Pension and post-retirement benefit costs	22,577			24,788
Alternative minimum tax credit carry forward	19,049			18,819
Property, plant and equipment	6,657			6,580
Accrued expenses	3,765			8,237
Inventories	6,425			5,366
Third-party products liability	568			636
Stock-based compensation expense	3,365			3,019
Other	5,373			8,457
Total deferred tax assets	$	107,059		$	100,944
Gross deferred tax liabilities:
Land and mineral property basis difference	$	(63,488	)	$	(65,217	)
Fixed assets and depreciation	(54,913		)	(53,383		)
Intangible assets	(8,049		)	(8,587		)
Other	(122		)	(1,211		)
Total deferred tax liabilities	$	(126,572	)	$	(128,398	)
Net deferred tax liabilities	(19,513		)	(27,454		)
Less: Net current deferred tax assets	—			22,295
Net long-term deferred tax liabilities	$	(19,513	)	$	(49,749	)

Summary of Effective Income Tax Rate on Pretax Earnings

	Years Ended December 31,
	2015			2014			2013
Income tax benefit (expense) computed at U.S. federal statutory rate	$	(41	)	$	(55,533	)	$	(33,606	)
Decrease (increase) resulting from:
Statutory depletion	8,918			15,548			10,595
Prior year tax return reconciliation	393			1,018			1,786
State income taxes, net of federal benefit	1,370			(3,416		)	(2,332		)
Domestic production deduction	—			3,911			2,327
Other, net	1,111			1,309			469
Income tax benefit (expense)	$	11,751		$	(37,163	)	$	(20,761	)