Acquisitions of Ownership Interests in Partner Companies and Funds - Additional Information (Detail) (USD $)	6 Months Ended		1 Months Ended	6 Months Ended	1 Months Ended		6 Months Ended	1 Months Ended			6 Months Ended	1 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Nov. 30, 2011 Mendivo, Inc.	Jun. 30, 2013 Mendivo, Inc.	May 31, 2013 Hoopla Software, Inc.	Dec. 31, 2011 Hoopla Software, Inc.	Jun. 30, 2013 Penn Mezzanine	Feb. 28, 2013 Clutch Holdings, LLC	Mar. 31, 2013 Lumesis, Inc.	Feb. 29, 2012 Lumesis, Inc.	Jun. 30, 2013 PixelOptics, Inc.	Feb. 28, 2013 Pneuron, Inc.	Jan. 31, 2013 Sotera Wireless, Inc.	Jun. 30, 2013 Alverix
Schedule Of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired	$ 15,131,000	$ 16,190,000	$ 6,300,000	$ 5,300,000				$ 500,000	$ 1,700,000	$ 2,200,000	$ 31,600,000	$ 5,000,000	$ 1,300,000	$ 8,800,000
Fund amount for participations in loan					200,000		2,200,000
Fund amount for participations in equity interests						1,300,000	100,000
Fund amount for participations in loan and equity interests							2,300,000
Ownership interest under equity method, percentage								6.50%				27.60%	7.70%
Convertible bridge loan											5,300,000			300,000
Acquired additional shares from a previous investor													$ 1,200,000