Segment Reporting (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues
Total revenues	$ 134,773	$ 127,558	$ 410,848	$ 398,901
Corporate (non-product)
Revenues
Total revenues	458	313	1,033	776
Electronic Brokerage
Revenues
Total revenues	68,663	66,234	214,740	210,597
Research Sales and Trading
Revenues
Total revenues	30,470	26,683	90,026	80,236
Platforms
Revenues
Total revenues	23,570	23,151	70,636	72,845
Analytics
Revenues
Total revenues	$ 11,612	$ 11,177	$ 34,413	$ 34,447