Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Segment information
Revenue	$ 51,239	$ 35,142	$ 132,947	$ 104,424
Net income (loss) attributable to ICG Group, Inc.	21,341	(2,957)	8,327	9,700
Components of Other
Corporate other income (loss) (Note 10)	31,226	39	32,853	26,504
Non controlling interest	387	(335)	(417)	(941)
Other Net Income Loss of Parent Entity			32,436	25,563
Assets
Total Assets	386,197		386,197		306,820
Core [Member]
Segment information
Revenue	51,239	35,142	132,947	104,424
Net income (loss) attributable to ICG Group, Inc.	(4,254)	297	(6,439)	447
Assets
Total Assets	326,124		326,124		172,416
Venture [Member]
Segment information
Net income (loss) attributable to ICG Group, Inc.	(1,049)	(1,070)	(3,541)	(2,941)
Assets
Total Assets	11,843		11,843		6,414
Total Segment [Member]
Segment information
Revenue	51,239	35,142	132,947	104,424
Net income (loss) attributable to ICG Group, Inc.	(5,303)	(773)	(9,980)	(2,494)
Assets
Total Assets	337,967		337,967		178,830
Dispositions [Member]
Segment information
Net income (loss) attributable to ICG Group, Inc.	(181)	(1,179)	(743)	(4,037)
Assets
Total Assets	0		0		743
Corporate [Member]
Segment information
Net income (loss) attributable to ICG Group, Inc.	(4,788)	(709)	(13,386)	(9,332)
Assets
Total Assets	48,230		48,230		127,247
Other [Member]
Segment information
Net income (loss) attributable to ICG Group, Inc.	31,613	(296)	32,436	25,563
Components of Other
Other Net Income Loss of Parent Entity	31,613	(296)
Assets
Total Assets