Ownership Interests in and Advances to Partner Companies and Funds - Carrying Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investments In And Advances To Affiliates [Line Items]
Equity method investments	$ 144,936	$ 135,989
Cost method investments	7,074	9,138
Advances to partner companies	10,978	9,065
Ownership interests in and advances to partner companies and funds ($19,363 and $20,972 at fair value at June 30,2013 and December 31,2012, respectively)	162,988	154,192
Partner companies [Member]
Investments In And Advances To Affiliates [Line Items]
Equity method investments	143,906	134,861
Cost method investments	5,024	6,774
Private equity funds [Member]
Investments In And Advances To Affiliates [Line Items]
Equity method investments	1,030	1,128
Cost method investments	$ 2,050	$ 2,364