Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Employee benefits	$ 829	$ 836
Inventories	3,902	2,309
Natural gas derivatives		610
Goodwill & other intangibles	2,350	3,179
Net operating loss	88,341	59,536
Foreign tax credits	667	667
Interest	2,200	552
Accrued expenses	3,496
Other	352	1,477
Total deferred tax assets	102,137	69,166
Deferred tax liabilities:
Depreciation	30,054	14,332
Indefinite-lived intangibles	817	209
Foreign		26
Total deferred tax liabilities	30,871	14,567
Valuation Allowance	72,380	54,829
Net deferred tax liabilities	$ (1,114)	$ (230)