Summary of Significant Accounting Principles - Prior Period Adjustment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net (loss) income	$ (5,037)	$ 4,739	$ (9,138)	$ 2,723
Contract revenues	140,162	164,017	416,339	433,941
Costs of contract revenues	129,405	139,849	377,200	378,116
Selling, general and administrative expenses	16,524	15,291	49,031	47,728
Income tax expense	$ (1,666)	$ 3,224	$ (4,309)	$ 1,972