Acquisitions of Ownership Interests in Partner Companies and Funds (Detail) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments				$ 3,250	$ 11,851
Equity method investments	$ 71,688			71,688		$ 108,089
InfoBionic
Schedule of Equity Method Investments [Line Items]
Equity method investments	21,300			21,300
Convertible bridge loan	700	$ 800	$ 800
meQuilibrium
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments	1,000
Equity method investments	10,500			10,500
Moxe Health
Schedule of Equity Method Investments [Line Items]
Equity method investments	4,500			4,500
Convertible bridge loan	1,000
Zipnosis
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments	1,500
Equity method investments	7,000			7,000
CloudMine
Schedule of Equity Method Investments [Line Items]
Equity method investments		10,500
Convertible bridge loan	400	500
Aktana, Inc.
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments	500
Equity method investments	9,700			9,700
QuanticMind, Inc.
Schedule of Equity Method Investments [Line Items]
Equity method investments	11,500			11,500
Convertible bridge loan	1,400
Sonobi
Schedule of Equity Method Investments [Line Items]
Equity method investments	10,900			$ 10,900
Convertible bridge loan	$ 500	1,500	200
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
Cask Data
Schedule of Equity Method Investments [Line Items]
Equity method investments			13,300
Convertible bridge loan		200	300
Novasom, Inc.
Schedule of Equity Method Investments [Line Items]
Equity method investments			25,400
Convertible bridge loan		$ 800	1,300
Spongecell
Schedule of Equity Method Investments [Line Items]
Equity method investments						18,600
Convertible bridge loan			500
BrickWork
Schedule of Equity Method Investments [Line Items]
Equity method investments						$ 4,200
Convertible bridge loan			$ 400