Income Taxes - Schedule of Deferred Income Taxes (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Accrued expenses	$ 313	$ 760
Allowance for doubtful accounts	208	184
Contract overrun reserves	294	1,776
Deferred compensation	177	507
Employment-related accruals	2,091	2,888
Environmental reserves	501	769
Federal tax credit carryforwards	5,613	4,234
Inventory reserves	1,315	2,313
Pension obligation	2,398	4,002
State net operating loss carryforwards	86	63
State tax credit carryforwards	9,051	6,585
Stock-based compensation	1,480	1,950
Workers’ compensation	75	122
Other	1,492	2,098
Total gross deferred tax assets	25,094	28,251
Valuation allowance	(9,013)	(6,607)
Total gross deferred tax assets, net of valuation allowance	16,081	21,644
Deferred tax liabilities:
Depreciation	(7,976)	(13,167)
Goodwill	(2,902)	(3,909)
Intangibles	(20,611)	(35,071)
Prepaid insurance	(312)	(626)
Unbilled receivables	0	(2)
Total gross deferred tax liabilities	(31,801)	(52,775)
Net deferred tax liabilities	$ (15,720)	$ (31,131)