Income Taxes - Summary of Tax Effects on Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 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)
Deferred income taxes, net	0	22,295
Net long-term deferred tax liabilities	$ (19,513)	$ (49,749)