Other Income (Loss) - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended						1 Months Ended	12 Months Ended						1 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	Dec. 31, 2011 ICG's Equity Based Compensation	Dec. 31, 2010 ICG's Equity Based Compensation	Dec. 31, 2011 Anthem	Jul. 11, 2012 Channel Intelligence	Dec. 31, 2012 Channel Intelligence	Dec. 31, 2011 Channel Intelligence	Dec. 31, 2012 GoIndustry	Dec. 31, 2012 Star Cite	Dec. 31, 2011 Star Cite	Dec. 31, 2011 Click Equations	Mar. 31, 2012 Metastorm	Nov. 30, 2011 Metastorm	Feb. 17, 2011 Metastorm	Dec. 31, 2012 Metastorm	Dec. 31, 2011 Metastorm	Dec. 31, 2012 Creditex	Dec. 31, 2010 Creditex	Dec. 31, 2012 Active	Dec. 31, 2010 Blackboard, Inc.
Schedule of Equity Method Investments [Line Items]
Gain on assets and liabilities acquired	$ 24,859,000	$ 31,569,000	$ 1,054,000	$ 397,000	$ 16,440,000	$ (374,000)	$ 1,612,000	$ 24,946,000	$ 57,879,000	$ 42,624,000	$ 74,147,000				$ 26,200,000
Increasing ICG's ownership interest greater than															42,700,000
Number of Shares Distributed has Escrowed Proceeds Related to the Disposition of a Former Company									12,989		47,056
Gains on sales/distributions of ownership interests									2,908,000	1,634,000	1,789,000	1,600,000	1,800,000														1,800,000	5,200,000
Sale Proceeds																		2,900,000		24,900,000				53,000,000
Carrying value of transaction costs																		0
Gain or Loss on sale																26,167,000		2,900,000	428,000	14,054,000	(803,000)			24,900,000	208,000	25,988,000	1,798,000	5,179,000
Common stock																				668,755
Common stock valued																				9,100,000
Closing price of stock																				$ 13.60
Cash consideration																				100,000
Shares of stock consideration																				102,199
Gain on acquisition																				14,100,000
Other receivables	405,000				22,679,000				405,000	22,679,000									400,000	22,700,000
Active common stock valued																				7,000,000
Equity method cash																			15,700,000	15,800,000
Active common stock																			513,663
Active common stock released from escrow																			83,627
Dilution gain (loss) on equity method companies										(496,000)	67,000						496,000
Sale proceeds received																								51,300,000
Escrowed proceeds received																						200,000	1,100,000
Gain on other distributions										1,856,000				1,490,000
Foreign currency gains									200,000	600,000	400,000
Sale of common stock																													447,057	1,619,571
Common stock price per share																													$ 16.88	$ 42.87
Proceed from sale of securities									7,632,000		74,383,000																		7,500,000	69,400,000
Realized gains on marketable securities									$ 1,446,000		$ 66,952,000