Summary of Significant Accounting Principles - Prior Period Adjustment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net (loss) income	$ (7,924)	$ 4,101
Contract revenues	143,105	136,843
Costs of contract revenues	132,886	121,021
Selling, general and administrative expenses	16,770	15,014
Income tax expense	$ 593	$ 1,489