Ownership Interests in and Advances to Partner Companies and Funds - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended	3 Months Ended
	Mar. 31, 2013 Private equity funds	Mar. 31, 2012 Private equity funds	Jun. 30, 2013 Nupathe	Jun. 30, 2013 Nupathe	Jun. 30, 2013 PixelOptics, Inc. Private equity funds	Jun. 30, 2012 PixelOptics, Inc. Private equity funds	Jun. 30, 2013 Penn Mezzanine	Jun. 30, 2012 Penn Mezzanine	Jun. 30, 2013 Penn Mezzanine Impairment charge related to loan participation	Jun. 30, 2012 Penn Mezzanine Impairment charge related to loan participation	Jun. 30, 2012 Penn Mezzanine Equity participation	Jun. 30, 2013 Penn Mezzanine Warrants	Jun. 30, 2012 Penn Mezzanine Warrants
Investment [Line Items]
Recognized impairment charges	$ 0.2	$ 0.4			$ 9.9	$ 3.7	$ 0.3	$ 0.7	$ 0.2	$ 0.2	$ 0.4	$ 0.1	$ 0.1
Recognition of unrealized loss (gain) on mark-to-market of ownership interests			$ 2.4	$ 1.6