Acquisitions - Narrative (Details) (USD $)	3 Months Ended		9 Months Ended			0 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Jun. 28, 2011 LaBranche and Co Inc. [Member]	Sep. 30, 2011 LaBranche and Co Inc. [Member]	Jun. 30, 2011 LaBranche and Co Inc. [Member]	Sep. 30, 2011 LaBranche and Co Inc. [Member]
Business Acquisition [Line Items]
Conversion ratio, shares of Company's stock issued per share of Acquiree's stock						0.9980
Shares issued in acquisition, value						$ 156,000,000
Closing stock price	$ 2.71		$ 2.71		$ 2.59	$ 3.82
Shares outstanding, in shares						40,931,997
Net assets acquired						175,982,000
Non compete agreements and covenants with limiting conditions acquired						2,310,000
Total purchase price						156,048,000
Bargain purchase gain recognized	0	0	0	22,244,000		22,244,000		22,244,000
Acquisition related costs							$ 600,000		$ 2,900,000