Summary of Selected Information Related to Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue	$ 48,662		$ 42,822		$ 95,001		$ 77,520
Net income (loss) attributable to ICG Group, Inc.	(6,858)		(5,994)		12,210		(13,014)
Assets	407,811				407,811				448,581
Core
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue	48,662		42,822		94,572		77,520
Net income (loss) attributable to ICG Group, Inc.	(3,052)		(1,723)		(8,849)		(2,312)
Assets	325,846				325,846				333,779
Venture
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue					429
Net income (loss) attributable to ICG Group, Inc.	(407)		(585)		(1,489)		(1,225)
Assets	16,615				16,615				17,822
Total Segment
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue	48,662		42,822		95,001		77,520
Net income (loss) attributable to ICG Group, Inc.	(3,459)		(2,308)		(10,338)		(3,537)
Assets	342,461				342,461				351,601
Dispositions
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue
Net income (loss) attributable to ICG Group, Inc.	100		(1,028)		27,696		(1,702)
Assets									82,505
Corporate
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue
Net income (loss) attributable to ICG Group, Inc.	(3,912)		(3,476)		(9,089)		(8,598)
Assets	65,350				65,350				14,475
Other
Segment Reporting Revenue Reconciling Item [Line Items]
Revenue		[1]		[1]		[1]		[1]
Net income (loss) attributable to ICG Group, Inc.	413	[1]	818	[1]	3,941	[1]	823	[1]
Assets

[1] The following table reflects the components in Other (in thousands):  Three Months Ended June 30,Six Months Ended June 30,  2013   2012   2013   2012  Corporate other income (loss) (Note 10)$(45)   $1,470    $(103)   $1,627   Noncontrolling interest (income) loss 458     (652)    4,044     (804)   $413    $818    $3,941    $823