Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Post-retirement obligations	$ 2,833	$ 1,123
Tax credits	1,693	1,787
Expenses not currently deductible	12,987	13,222
Net operating loss carryover	5,228	5,629
Other	994	771
Total deferred tax assets	23,735	22,532
Valuation allowance for deferred tax assets	(6,183)	(6,728)
Net deferred tax assets	17,552	15,804
Deferred tax liabilities:
Property, plant and equipment	21,982	17,737
Intangible assets	39,044	19,989
Basis difference - convertible debt	7,670	12,741
Goodwill	7,430	6,321
Total deferred liabilities	76,126	56,788
Net deferred tax liabilities	$ 58,574	$ 40,984