Net Income (Loss) per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Basic and Diluted:
Net income (loss) attributable to ICG Group, Inc.	$ 21,341	$ (2,957)	$ 8,327	$ 9,700
Basic:
Net income (loss) attributable to ICG Group, Inc. per share	$ 0.60	$ (0.08)	$ 0.23	$ 0.26
Diluted:
Net income (loss) per diluted share attributable to ICG Group, Inc.	$ 0.59	$ (0.08)	$ 0.23	$ 0.26
Shares used in computation of basic income (loss) per share	35,650	36,556	35,907	36,819
Shares used in computation of diluted income (loss) per share	36,273	36,556	36,435	37,738
Stock options [Member]
Diluted:
Number of dilutive shares	52		55	93
Restricted Stock [Member]
Diluted:
Number of dilutive shares	39		25	23
DSUs [Member]
Diluted:
Number of dilutive shares	21		23	13
SARs [Member]
Diluted:
Number of dilutive shares	511		425	790