Calculations of Net Income (Loss) Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Amounts attributable to ICG Group, Inc.:
Income (loss) from continuing operations	$ (7,516)	$ 20,125	$ (26,809)	$ 2,205
Income (loss) from discontinued operations	4,184	1,216	35,687	6,122
Net income (loss) attributable to ICG Group, Inc.	$ (3,332)	$ 21,341	$ 8,878	$ 8,327
Basic income (loss) per share attributable to ICG Group, Inc.:
Income (loss) from continuing operations	$ (0.21)	$ 0.57	$ (0.74)	$ 0.06
Income (loss) from discontinued operations	$ 0.12	$ 0.03	$ 0.98	$ 0.17
Net income (loss) attributable to ICG Group, Inc. per share	$ (0.09)	$ 0.60	$ 0.24	$ 0.23
Diluted income (loss) per share attributable to ICG Group, Inc.:
Income (loss) from continuing operations	$ (0.21)	$ 0.56	$ (0.74)	$ 0.06
Income (loss) from discontinued operations	$ 0.12	$ 0.03	$ 0.98	$ 0.17
Net income (loss) attributable to ICG Group, Inc. per share	$ (0.09)	$ 0.59	$ 0.24	$ 0.23
Shares used in computation of basic income (loss) per share	36,303	35,650	36,494	35,907
Shares used in computation of diluted income (loss) per share	36,303	36,273	36,494	36,435
SARs
Diluted income (loss) per share attributable to ICG Group, Inc.:
Shares used in computation of diluted income (loss) per share		511		425
Stock Options
Diluted income (loss) per share attributable to ICG Group, Inc.:
Shares used in computation of diluted income (loss) per share		52		55
Restricted Stock
Diluted income (loss) per share attributable to ICG Group, Inc.:
Shares used in computation of diluted income (loss) per share		39		25
DSUs
Diluted income (loss) per share attributable to ICG Group, Inc.:
Shares used in computation of diluted income (loss) per share		21		23