Supplemental Financial Information (Tables)

12 Months Ended

Dec. 31, 2012

Supplemental Financial Information [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

	Quarter Ended
	March 31, 2012		June 30, 2012			Sept. 30, 2012			December 31, 2012
	(in thousands)
Total revenues	$	57,480	$	59,470		$	57,598		$	65,932
Net Income (loss) before income taxes	6,378		(10,189		)	(11,455		)	(8,243		)
Income tax expense (benefit)	142		191			163			(48		)
Net income (loss) from continuing operations	6,236		(10,380		)	(11,618		)	(8,195		)
Net income (loss) from discontinued operations, net of tax	—		—			—			—
Net Income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries	2,241		(2,434		)	(1,033		)	1,154
Net income (loss) attributable to Cowen Group, Inc. stockholders	$	3,995	$	(7,946	)	$	(10,585	)	$	(9,349	)
Earnings (loss) per share:
Basic
Income (loss) from continuing operations	$	0.03	$	(0.07	)	$	(0.09	)	$	(0.08	)
Income (loss) from discontinued operations	—		—			—			—
Diluted
Income (loss) from continuing operations	$	0.03	$	(0.07	)	$	(0.09	)	$	(0.08	)
Income (loss) from discontinued operations	—		—			—			—
Weighted average number of common shares:
Basic	114,281		114,561			114,989			113,939
Diluted	115,663		114,561			114,989			113,939

	Quarter Ended
	March 31, 2011		June 30, 2011			Sept. 30, 2011			December 31, 2011
	(in thousands)
Total revenues	$	64,245	$	58,679		$	61,959		$	50,395
Net Income (loss) before income taxes	1,043		4,541			(43,858		)	(60,336		)
Income tax expense (benefit)	163		(17,954		)	71			(2,353		)
Net income (loss) from continuing operations	880		22,495			(43,929		)	(57,983		)
Net income (loss) from discontinued operations, net of tax	—		—			(5,087		)	(18,559		)
Net Income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries	798		2,458			(783		)	3,354
Net income (loss) attributable to Cowen Group, Inc. stockholders	$	82	$	20,037		$	(48,233	)	$	(79,896	)
Earnings (loss) per share:
Basic
Income (loss) from continuing operations	$	0.00	$	0.25		$	(0.37	)	$	(0.54	)
Income (loss) from discontinued operations	—		—			(0.04		)	(0.16		)
Diluted
Income (loss) from continuing operations	$	0.00	$	0.26		$	(0.37	)	$	(0.54	)
Income (loss) from discontinued operations	—		—			(0.04		)	(0.17		)
Weighted average number of common shares:
Basic	74,160		76,330			115,664			95,532
Diluted	76,083		77,898			115,664			95,532