Summary of Selected Information Related to Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	$ 43,584	$ 45,489	$ 42,822	$ 34,698	$ 34,435	$ 33,427	$ 33,531	$ 32,044	$ 166,593		$ 133,437		$ 109,213
Net income (loss) attributable to ICG Group, Inc.	14,662	21,341	(5,994)	(7,020)	17,866	(2,957)	(3,233)	15,890	22,989		27,566		46,589
Assets	447,759				306,820				447,759		306,820		280,989
Core
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue									166,593		133,437		109,213
Net income (loss) attributable to ICG Group, Inc.									(9,312)		10,951		330
Assets	337,775				174,964				337,775		174,964		148,393
Venture
Segment Reporting, Revenue Reconciling Item [Line Items]
Net income (loss) attributable to ICG Group, Inc.									(1)		(699)		(572)
Assets	13,007				11,563				13,007		11,563		2,968
Reportable Segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue									166,593		133,437		109,213
Net income (loss) attributable to ICG Group, Inc.									(9,313)		10,252		(242)
Assets	350,782				186,527				350,782		186,527		151,361
Dispositions
Segment Reporting, Revenue Reconciling Item [Line Items]
Net income (loss) attributable to ICG Group, Inc.									(4,890)		(10,121)		(13,856)
Assets	82,505				3,866				82,505		3,866		43,083
Corporate
Segment Reporting, Revenue Reconciling Item [Line Items]
Net income (loss) attributable to ICG Group, Inc.									(20,042)		(13,537)		(12,501)
Assets	14,475				116,427				14,475		116,427		86,545
Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Net income (loss) attributable to ICG Group, Inc.									$ 57,234	[1]	$ 40,972	[1]	$ 73,188	[1]

[1] The following table reflects the components in Other (in thousands): Year Ended December 31, 2012 2011 2010 Corporate other income (loss) (Note 13) $ 57,826 $ 43,207 $ 74,507 Noncontrolling interest (592 ) (2,235 ) (1,319 ) $ 57,234 $ 40,972 $ 73,188