Segment Reporting (Details 2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues
Total revenues	$ 140,494	$ 138,466	$ 290,221	$ 276,075
Corporate
Revenues
Total revenues	229	279	462	576
Electronic Brokerage
Revenues
Total revenues	75,048	73,192	155,502	146,076
Research Sales and Trading
Revenues
Total revenues	30,379	30,311	62,892	59,556
Platforms
Revenues
Total revenues	23,550	23,333	48,623	47,066
Analytics
Revenues
Total revenues	$ 11,288	$ 11,351	$ 22,742	$ 22,801