Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Employee benefits	$ 836	$ 1,349
Inventories	2,309	8,811
Natural gas derivatives	610	1,281
Goodwill & other intangibles	3,179	4,881
Net operating loss	59,536	51,722
Foreign tax credits	667
Other	2,029	2,028
Total deferred tax assets	69,166	70,072
Deferred tax liabilities:
Depreciation	14,332	71,308
Indefinite-lived intangibles	209
Foreign	26
Total deferred tax liabilities	14,567	71,308
Valuation Allowance	54,829
Net deferred tax liabilities	$ (230)	$ (1,236)