Acquisitions of Ownership Interests in Partner Companies and Funds (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments			$ 250	$ 8,026
Equity method investments	$ 78,516		$ 78,516		$ 108,089
Novasom, Inc.
Schedule of Equity Method Investments [Line Items]
Equity method investments		$ 25,400
Convertible bridge loan	800	1,300
InfoBionic
Schedule of Equity Method Investments [Line Items]
Equity method investments		20,500
Convertible bridge loan	800	800
CloudMine
Schedule of Equity Method Investments [Line Items]
Equity method investments		10,000
Convertible bridge loan	500
Spongecell
Schedule of Equity Method Investments [Line Items]
Equity method investments					18,600
Convertible bridge loan		500
WebLinc
Schedule of Equity Method Investments [Line Items]
Equity method investments		14,500
Convertible bridge loan	200	500
Propeller
Schedule of Equity Method Investments [Line Items]
Equity method investments		14,000
Convertible bridge loan	300
BrickWork
Schedule of Equity Method Investments [Line Items]
Equity method investments					$ 4,200
Convertible bridge loan		400
Cask Data
Schedule of Equity Method Investments [Line Items]
Equity method investments		13,300
Convertible bridge loan	200	300
Sonobi
Schedule of Equity Method Investments [Line Items]
Equity method investments		9,400
Convertible bridge loan	$ 1,500	$ 200