Income Taxes - Schedule of Deferred Income Taxes (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Accrued expenses	$ 704	$ 313
Allowance for doubtful accounts	267	208
Contract overrun reserves	1,263	294
Deferred compensation	302	177
Employment-related accruals	4,252	2,091
Environmental reserves	479	501
Federal tax credit carryforwards	288	5,613
Inventory reserves	1,757	1,315
Pension obligation	2,324	2,398
State net operating loss carryforwards	51	86
State tax credit carryforwards	9,075	9,051
Stock-based compensation	1,661	1,480
Workers’ compensation	51	75
Other	1,538	1,492
Total gross deferred tax assets	24,012	25,094
Valuation allowance	(9,083)	(9,013)
Total gross deferred tax assets, net of valuation allowance	14,929	16,081
Deferred tax liabilities:
Deferred revenue	(649)	0
Depreciation	(7,951)	(7,976)
Goodwill	(3,963)	(2,902)
Intangibles	(19,905)	(20,611)
Prepaid insurance	(223)	(312)
Total gross deferred tax liabilities	(32,691)	(31,801)
Net deferred tax liabilities	$ (17,762)	$ (15,720)