Segment Analysis (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Information concerning assets
Total Assets	$ 1,447,716	$ 3,303,556
Reportable segments
Information concerning assets
Total Assets	1,409,928	3,213,075
MBS & Rates
Information concerning assets
Total Assets	1,260,724	2,929,879
Credit Products
Information concerning assets
Total Assets	34,719	29,930
Investment Banking
Information concerning assets
Total Assets	8,597	10,916
ClearPoint
Information concerning assets
Total Assets	105,888	242,350
Other
Information concerning assets
Total Assets	69,880	126,358
Intersegment eliminations
Information concerning assets
Total Assets	$ (32,092)	$ (35,877)