Segment Reporting - Revenue by Product Group (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Total Revenues	$ 126,747	$ 114,531	$ 121,581	$ 120,835	$ 119,589	$ 104,185	$ 120,610	$ 124,668	$ 483,694	$ 469,052	$ 634,803
Execution Services
Revenues
Total Revenues									344,192	328,252	386,158
Workflow Technology
Revenues
Total Revenues									92,533	92,891	94,117
Analytics
Revenues
Total Revenues									45,249	44,198	45,891
Corporate
Revenues
Total Revenues									$ 1,720	$ 3,711	$ 108,637