Shareholder's Equity and Stock-Based Compensation - Summary of Stock-Based Compensation Expense Recognized in Statements of Operations Related to All Outstanding Stock Based Compensation Awards (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,467	$ 1,034
Total Direct Costs
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	843	542
Selling, General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 624	$ 492