Ownership Interests in and Advances to Partner Companies and Funds - Narrative (Detail) (USD $)					3 Months Ended	9 Months Ended	3 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Private equity funds [Member]	Dec. 31, 2012 Private equity funds [Member]	Sep. 30, 2013 Nupathe [Member]	Sep. 30, 2013 Nupathe [Member]	Sep. 30, 2013 PixelOptics, Inc. [Member]	Jun. 30, 2013 PixelOptics, Inc. [Member]	Jun. 30, 2012 PixelOptics, Inc. [Member]	Jun. 30, 2013 Penn Mezzanine [Member]
Investment [Line Items]
Recognized impairment charges							$ 1,300,000	$ 9,900,000	$ 3,700,000	$ 300,000
Equity method investments	111,855,000	106,741,000	3,606,000	3,810,000			0
Recognition of unrealized loss (gain) on mark-to-market of ownership interests					$ 4,800,000	$ 6,400,000