Calculations of Net Income (Loss) Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Amounts attributable to ICG Group, Inc.:
Net income (loss) from continuing operations	$ 2,804		$ (8,022)		$ (9,025)		$ (11,426)		$ 13,449		$ 16,063		$ (9,156)		$ (7,660)		$ (25,669)	$ 12,703	$ 10,682
Net income (loss) from discontinued operations	197,377		4,690		2,167		30,494		1,213		5,278		3,162		640		234,728	10,286	16,884
Net income (loss)	$ 200,181		$ (3,332)		$ (6,858)		$ 19,068		$ 14,662		$ 21,341		$ (5,994)		$ (7,020)		$ 209,059	$ 22,989	$ 27,566
Basic income (loss) per share attributable to ICG Group, Inc.:
Income (loss) from continuing operations	$ 0.08	[1]	$ (0.22)	[1]	$ (0.25)	[1]	$ (0.31)	[1]	$ 0.37	[1]	$ 0.45	[1]	$ (0.26)	[1]	$ (0.21)	[1]	$ (0.70)	$ 0.35	$ 0.29
Income (loss) from discontinued operations	$ 5.38	[1]	$ 0.13	[1]	$ 0.06	[1]	$ 0.83	[1]	$ 0.04	[1]	$ 0.15	[1]	$ 0.09	[1]	$ 0.02	[1]	$ 6.42	$ 0.29	$ 0.46
Net income (loss) attributable to ICG Group, Inc. per share	$ 5.46	[1]	$ (0.09)	[1]	$ (0.19)	[1]	$ 0.52	[1]	$ 0.41	[1]	$ 0.60	[1]	$ (0.17)	[1]	$ (0.19)	[1]	$ 5.72	$ 0.64	$ 0.75
Diluted income (loss) per share attributable to ICG Group, Inc.:
Income (loss) from continuing operations	$ 0.08	[1]	$ (0.22)	[1]	$ (0.25)	[1]	$ (0.31)	[1]	$ 0.36	[1]	$ 0.44	[1]	$ (0.26)	[1]	$ (0.21)	[1]	$ (0.70)	$ 0.35	$ 0.29
Income (loss) from discontinued operations	$ 5.10	[1]	$ 0.13	[1]	$ 0.06	[1]	$ 0.83	[1]	$ 0.04	[1]	$ 0.15	[1]	$ 0.09	[1]	$ 0.02	[1]	$ 6.42	$ 0.28	$ 0.45
Net income (loss) attributable to ICG Group, Inc. per share	$ 5.18	[1]	$ (0.09)	[1]	$ (0.19)	[1]	$ 0.52	[1]	$ 0.40	[1]	$ 0.59	[1]	$ (0.17)	[1]	$ (0.19)	[1]	$ 5.72	$ 0.63	$ 0.74
Shares used in computation of basic income (loss) per share	36,664	[1]	36,303	[1]	36,468	[1]	36,713	[1]	35,840	[1]	35,650	[1]	35,917	[1]	36,156	[1]	36,536	35,890	36,656
Incremental Diluted Shares Impact:
Shares used in computation of diluted income (loss) per share	38,680	[1]	36,303	[1]	36,468	[1]	36,713	[1]	36,912	[1]	36,273	[1]	35,917	[1]	36,156	[1]	36,536	36,543	37,460
Stock Options
Incremental Diluted Shares Impact:
Shares used in computation of diluted income (loss) per share																		41	84
SARs
Incremental Diluted Shares Impact:
Shares used in computation of diluted income (loss) per share																		546	683
Restricted Stock
Incremental Diluted Shares Impact:
Shares used in computation of diluted income (loss) per share																		40	20
DSUs
Incremental Diluted Shares Impact:
Shares used in computation of diluted income (loss) per share																		26	17

[1] The sum of quarterly income (loss) per share differs from the full year amount due to changes in the number of shares outstanding during the year.