Summary of Significant Accounting Principles - Revenue Recognition (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue, Major Customer [Line Items]
Costs and estimated earnings in excess of billings on uncompleted contracts	$ 57,411		$ 57,411		$ 47,389	$ 46,006
Billings in excess of costs and estimated earnings on uncompleted contracts	24,528		24,528		35,668	33,923
Deferred income taxes	12,682		12,682		13,167	13,243
Retained earnings	62,555		62,555		62,561	62,847
Contract revenues	125,073	$ 140,162	421,682	$ 416,339
Costs of contract revenues	119,135	129,405	379,154	377,200
Gross profit	5,938	10,757	42,528	39,139
Income tax (benefit) expense	(3,071)	(1,666)	78	(4,309)
Net loss	$ (6,356)	$ (5,037)	$ (6)	$ (9,138)
Basic (loss) income per share (in dollars per share)	$ (0.22)	$ (0.18)	$ 0.00	$ (0.33)
Diluted (loss) income per share (in dollars per share)	$ (0.22)	$ (0.18)	$ 0.00	$ (0.33)
Customer One
Revenue, Major Customer [Line Items]
Contract revenues			$ 15,500
Before ASC 606
Revenue, Major Customer [Line Items]
Costs and estimated earnings in excess of billings on uncompleted contracts	$ 58,232		58,232			46,006
Billings in excess of costs and estimated earnings on uncompleted contracts	25,731		25,731			33,923
Deferred income taxes	12,545		12,545			13,243
Retained earnings	62,310		62,310			$ 62,847
Contract revenues			420,479
Costs of contract revenues			378,333
Gross profit			42,146
Income tax (benefit) expense			(59)
Net loss			$ (251)
Basic (loss) income per share (in dollars per share)			$ (0.01)
Diluted (loss) income per share (in dollars per share)			$ (0.01)
Accounting Standards Update 2014-09 | ASC 606 Adjustments
Revenue, Major Customer [Line Items]
Costs and estimated earnings in excess of billings on uncompleted contracts	(821)		$ (821)		1,383
Billings in excess of costs and estimated earnings on uncompleted contracts	(1,203)		(1,203)		1,745
Deferred income taxes	137		137		(76)
Retained earnings	$ 245		245		$ (286)
Contract revenues			1,203
Costs of contract revenues			821
Gross profit			382
Income tax (benefit) expense			137
Net loss			$ 245
Basic (loss) income per share (in dollars per share)			$ 0.01
Diluted (loss) income per share (in dollars per share)			$ 0.01