Segment Reporting (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues
Total revenues	$ 131,900	$ 127,558	$ 139,293	$ 132,050	$ 121,534	$ 119,617	$ 126,910	$ 136,375	$ 530,801	$ 504,436	$ 572,037
Corporate (non-product)
Revenues
Total revenues									1,457	1,285
Electronic Brokerage
Revenues
Total revenues									279,830	250,882
Research Sales and Trading
Revenues
Total revenues									107,383	106,427
Platforms
Revenues
Total revenues									96,127	99,334
Analytics
Revenues
Total revenues									$ 46,004	$ 46,508