Summary of Selected Information Related to Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue	$ 16,071		$ 7,998		$ 41,521		$ 17,609
Net income (loss) attributable to ICG Group, Inc.	(3,332)		21,341		8,878		8,327
Assets	407,855				407,855				447,059
Operating Segments
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue	16,071		7,998		41,521		17,609
Net income (loss) attributable to ICG Group, Inc.	(4,347)		(6,203)		(15,997)		(16,122)
Assets	215,347				215,347				202,982
Operating Segments | Core
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue	16,071		7,384		41,092		16,995
Net income (loss) attributable to ICG Group, Inc.	(3,953)		(4,592)		(14,114)		(13,286)
Assets	198,476				198,476				185,160
Operating Segments | Venture
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue			614		429		614
Net income (loss) attributable to ICG Group, Inc.	(394)		(1,611)		(1,883)		(2,836)
Assets	16,871				16,871				17,822
Dispositions
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue
Net income (loss) attributable to ICG Group, Inc.	4,474		1,399		33,991		6,479
Assets	143,101				143,101				229,605
Corporate
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue
Net income (loss) attributable to ICG Group, Inc.	(4,372)		(5,468)		(13,970)		(14,466)
Assets	49,407				49,407				14,472
Other
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue		[1]		[1]		[1]		[1]
Net income (loss) attributable to ICG Group, Inc.	913	[1]	31,613	[1]	4,854	[1]	32,436	[1]
Assets

[1] (1) The following table reflects the components in Other (in thousands):  Three Months Ended September 30,Nine Months Ended September 30,  2013   2012   2013   2012  Corporate other income (loss) (Note 11)$6   $31,226    $(97)   $32,853   Noncontrolling interest (income) loss 907     387    4,951    (417)   $913    $31,613    $4,854    $32,436