Ownership Interests and Cost Method Companies - Additional Information (Detail) (USD $)	3 Months Ended				9 Months Ended							9 Months Ended		3 Months Ended	9 Months Ended			3 Months Ended	9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012	Dec. 31, 2012 Marketable securities	Dec. 31, 2012 Prepaid Expenses and Other Current Assets	Sep. 30, 2013 Active	Sep. 30, 2012 Active	Sep. 30, 2012 Intercontinental Exchange	Sep. 30, 2013 Intercontinental Exchange	Sep. 30, 2012 Intercontinental Exchange	Sep. 30, 2013 Anthem	Sep. 30, 2012 Go Industry	Sep. 30, 2012 Go Industry	Sep. 30, 2012 Bolt	Dec. 31, 2011 Bolt
Schedule Of Equity Method Investments [Line Items]
Net asset of equity method	$ 16,500,000				$ 16,500,000				$ 15,300,000
Net asset allocated of equity method goodwill	14,300,000				14,300,000				12,000,000
Allocated of equity method intangible	2,200,000				2,200,000				3,300,000
Amortized period					5 years		5 years
Amortization of intangible assets	(48,000)	[1]	(283,000)	[2]	(117,000)	[3]	(875,000)	[2]
Acquired preferred stock																				9,000,000
Equity method investment, ownership percentage																	9.00%			38.00%	26.00%
Fair value of active common stock remaining									700,000	300,000	400,000
Sale of common stock, shares												150,233	447,057
Common stock price per share												$ 5.10	$ 16.88
Proceeds from sales of marketable securities					760,000		7,632,000					800,000	7,500,000		1.8
Gain on sale of securities												100,000	1,400,000		100,000
Number of Shares Distributed has Escrowed Proceeds Related to the Disposition of a Former Company			12,989				12,989							12,989		12,989
Gains on sales/distributions of ownership interests			1,700,000				1,700,000							1,700,000		1,700,000
Carrying value of holdings in cost method companies	15,700,000				15,700,000				13,000,000
Sale proceeds																		2,900,000	2,900,000
Carrying value of transaction costs																		0	0
Equity loss																		$ (200,000)	$ (700,000)

[1] Includes Acquirgy, CIML, Freeborders and WhiteFence.

[2] Includes Acquirgy, Bolt, CIML, Freeborders, GoIndustry-DoveBid plc (“GoIndustry”) (to July 5, 2012, the date of disposition) and WhiteFence.

[3] Includes Acquirgy, CIML (from February 20, 2013, the date of deconsolidation), Freeborders and WhiteFence.