Acquisitions of Ownership Interests in Partner Companies and Funds (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 48,734	$ 64,489
InfoBionic
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan	400
Equity method investments		16,300
Sonobi
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan	2,000
Equity method investments		11,400
Novasom, Inc.
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan	700
Equity method investments		26,400
WebLinc
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan	$ 900
Equity method investments		$ 15,000