Summary of Significant Accounting Principles - Revenue Recognition (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Revenue, Major Customer [Line Items]
Costs and estimated earnings in excess of billings on uncompleted contracts	$ 23,641		$ 23,641		$ 9,217
Billings in excess of costs and estimated earnings on uncompleted contracts	51,964		51,964		21,761
Deferred income taxes	92		92		49
Retained loss	(41,418)		(41,418)		$ (31,861)
Contract revenues	165,985	$ 159,767	309,090	$ 296,610
Costs of contract revenues	151,008	140,305	285,031	262,452
Gross profit	14,977	19,462	24,059	34,158
Income tax (benefit) expense	(140)	1,660	453	3,149
Net (loss) income	$ (1,633)	$ 2,249	$ (9,557)	$ 6,350
Basic (loss) income per share (in dollars per share)	$ (0.06)	$ 0.08	$ (0.33)	$ 0.22
Diluted (loss) income per share (in dollars per share)	$ (0.06)	$ 0.08	$ (0.33)	$ 0.22
Customer One
Revenue, Major Customer [Line Items]
Contract revenues			$ 1,100