Summary of Significant Accounting Principles - Prior Period Adjustment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss	$ (6,356)	$ (5,037)	$ (6)	$ (9,138)
Contract revenues	125,073	140,162	421,682	416,339
Costs of contract revenues	119,135	129,405	379,154	377,200
Selling, general and administrative expenses	14,371	16,524	46,249	49,031
Income tax (benefit) expense	$ (3,071)	$ (1,666)	$ 78	$ (4,309)