Organization and Basis of Presentation (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) segment item	Dec. 31, 2017 USD ($)
Number of reportable operating segments | segment	4
Retained Earnings (Accumulated Deficit) | $	$ 488,993	$ 486,957
Minimum
Number of countries in which execution services are offered | item	50