Organization and Basis of Presentation (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) item	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) segment item	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Number of reportable operating segments | segment			4
Income tax benefit	$ (444)	$ 4,441	$ 1,047	$ 5,573
Retained earnings	540,986		540,986		$ 536,350
Increase in deferred tax assets	46,619		46,619		38,688
Additional paid-in capital	242,236		242,236		$ 248,748
ASU 2016-09
Income tax benefit	100		1,200
Retained earnings	600		600
Increase in deferred tax assets	300		300
Additional paid-in capital	$ 900		$ 900
Minimum
Number of countries in which execution services are offered | item	50		50