Goodwill and Intangible Assets (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended						0 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 RangeMark	Dec. 31, 2011 Segment, Equities	Dec. 31, 2012 Segment, MBS & Rates	Dec. 31, 2010 Segment, MBS & Rates	Aug. 22, 2011 Segment, Investment Banking item	Dec. 31, 2012 Segment, Investment Banking	Dec. 31, 2011 Segment, Investment Banking
Changes in the carrying amount of goodwill
Goodwill at the beginning of the period	$ 21,096	$ 105,694		$ 8,928	$ 17,364	$ 17,364		$ 3,732	$ 79,402
Impairment of goodwill	(21,096)	(84,598)		(8,928)	(17,364)			(3,732)	(75,670)
RangeMark acquisition			1,212		1,212
Goodwill at the end of the period	$ 1,212	$ 21,096			$ 1,212	$ 17,364			$ 3,732
Number of investment banking employees terminated							32