Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Pension, postretirement and other benefits	$ 57,700	$ 78,194
Capitalized expenditures	1,471	1,001
Deferred Tax Assets, Capital Loss Carryforwards	13,780	0
Net operating loss and tax credit carryforwards	145,528	132,057
All other items	38,205	29,826
Total deferred tax assets	256,684	241,078
Deferred tax liabilities:
Property, plant and equipment	(21,507)	(30,310)
Intangibles	(9,665)	(16,210)
All other items	(11,834)	(7,623)
Total deferred tax liabilities	(43,006)	(54,143)
Valuation allowances	(189,355)	(149,757)
Net deferred tax assets	$ 24,323	$ 37,178