Income Taxes - Schedule of Deferred Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Accrued expenses	$ 776	$ 704
Allowance for doubtful accounts	314	267
Contract overrun reserves	1,004	1,263
Deferred compensation	94	302
Employment-related accruals	5,049	4,252
Environmental reserves	494	479
Federal tax credit carryforwards	84	288
Inventory reserves	2,334	1,757
Pension obligation	2,552	2,324
Federal and state net operating loss carryforwards	6,251	51
State tax credit carryforwards	8,900	9,075
Stock-based compensation	1,672	1,661
Workers’ compensation	43	51
Other	1,409	1,538
Total gross deferred tax assets	30,976	24,012
Valuation allowance	(9,375)	(9,083)
Total gross deferred tax assets, net of valuation allowance	21,601	14,929
Deferred tax liabilities:
Deferred revenue	(256)	(649)
Depreciation	(8,852)	(7,951)
Goodwill	(4,109)	(3,963)
Intangibles	(24,749)	(19,905)
Prepaid insurance	(346)	(223)
Total gross deferred tax liabilities	(38,312)	(32,691)
Net deferred tax liabilities	$ (16,711)	$ (17,762)