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, 2018	Dec. 31, 2017
Investments in and Advances to Affiliates [Line Items]
Equity method investments	$ 64,489	$ 108,089
Cost method investments	15,771	4,096
Advances to partner companies	15,325	22,506
Total	95,585	134,691
Partner companies [Member]
Investments in and Advances to Affiliates [Line Items]
Equity method investments	64,097	107,646
Cost method investments	15,260	2,762
Private equity funds [Member]
Investments in and Advances to Affiliates [Line Items]
Equity method investments	392	443
Cost method investments	$ 511	$ 1,334