Acquisitions of Ownership Interests in Partner Companies and Funds - Additional Information (Detail) (USD $)	9 Months Ended			1 Months Ended	9 Months Ended	1 Months Ended		6 Months Ended	1 Months Ended		9 Months Ended		1 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2012 Alverix [Member]	Sep. 30, 2013 Alverix [Member]	Aug. 31, 2013 Quantia, Inc. [Member]	Aug. 31, 2013 Drive Factor [Member]	Jun. 30, 2013 Drive Factor [Member]	Aug. 31, 2013 Clutch Holdings, LLC [Member]	Feb. 28, 2013 Clutch Holdings, LLC [Member]	Sep. 30, 2013 Penn Mezzanine [Member]	Sep. 30, 2013 PixelOptics, Inc. [Member]	Jun. 30, 2013 Medivo Inc [Member]	Nov. 30, 2011 Medivo Inc [Member]	May 31, 2013 Hoopla Software, Inc. [Member]	Dec. 31, 2011 Hoopla Software, Inc. [Member]	Mar. 31, 2013 Lumesis, Inc. [Member]	Feb. 29, 2012 Lumesis, Inc. [Member]	Feb. 28, 2013 Pneuron, Inc. [Member]	Jul. 31, 2013 Crescendo [Member]	Dec. 31, 2012 Crescendo [Member]	Jan. 31, 2013 Sotera [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan					$ 600,000							$ 5,300,000			$ 200,000					$ 1,000,000
Payments to Acquire Other Investments																					10,000,000	1,300,000
Acquisitions of ownership interests in companies and funds, net of cash acquired	28,718,000	21,719,000		8,800,000		7,500,000	1,100,000	3,500,000	5,000,000	500,000		31,600,000	5,300,000	6,300,000		1,300,000	1,700,000	2,200,000	5,000,000
Equity method investments	111,855,000		106,741,000									0
Ownership interest under cost method, percentage										6.50%												7.70%
Ownership interest under equity method, percentage						34.40%			24.00%										27.60%
Fund amount for participations in loan and equity interests											2,300,000
Fund amount for participations in loan											2,200,000
Fund amount for participations in equity interests											100,000
Cost of shares acquired from previous investor																						$ 1,200,000