Ownership Interests in and Advances to Partner Companies and Funds - Summary of the carrying value of the Company's ownership interests in and advances to partner companies and private equity funds (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments in and Advances to Affiliates [Line Items]
Equity method investments	$ 108,089	$ 154,666
Cost method investments	4,096	3,662
Advances to partner companies	22,506	25,142
Total	134,691	183,470
Partner companies [Member]
Investments in and Advances to Affiliates [Line Items]
Equity method investments	107,646	154,219
Cost method investments	2,762	2,112
Private equity funds [Member]
Investments in and Advances to Affiliates [Line Items]
Equity method investments	443	447
Cost method investments	$ 1,334	$ 1,550