Segment Reporting - Revenue by Product Group (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Total revenues	$ 128,746	$ 120,769	$ 128,477	$ 131,484	$ 126,747	$ 114,531	$ 121,581	$ 120,835	$ 509,476	$ 483,694	$ 469,052
Revenue in Analytics for functionality but not a separate performance obligation from products and services provided by Workflow Technology and Execution Services									2,100
Execution Services
Revenues
Total revenues									359,300	344,192	328,252
Workflow Technology
Revenues
Total revenues									104,064	92,533	92,891
Analytics
Revenues
Total revenues									43,108	45,249	44,198
Corporate
Revenues
Total revenues									$ 3,004	$ 1,720	$ 3,711