Income Taxes - Components of Company's Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Postretirement and other employee benefits	$ 94,581	$ 97,269
Product liability	30,791	27,922
Net operating loss, capital loss, and tax credit carryforwards	14,291	11,064
All other items	37,296	29,375
Total deferred tax assets	176,959	165,630
Deferred tax liabilities:
Property, plant and equipment	(117,148)	(108,668)
All other items	(6,141)	(6,196)
Total deferred tax liabilities	(123,289)	(114,864)
Deferred tax assets (liabilities), net, total	53,670	50,766
Valuation allowances	(27,270)	(22,620)
Net deferred tax asset	$ 26,400	$ 28,146