Pro Forma Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Dilutive Securities Included In Computation Of Earnings Per Share [Line Items]
Revenue	$ 17,300	$ 12,900	$ 48,300	$ 34,500
Net income (loss) attributable to ICG Group, Inc.	$ (3,300)	$ 20,900	$ 9,000	$ 6,300
Net income (loss) per diluted share attributable to ICG Group, Inc.	$ (0.09)	$ 0.57	$ 0.25	$ 0.17