Acquisitions of Ownership Interests in Partner Companies and Funds (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments	$ 0	$ 4,476
Equity method investments	99,353		$ 108,089
Novasom, Inc.
Schedule of Equity Method Investments [Line Items]
Equity method investments			24,100
Convertible bridge loan	1,300
InfoBionic
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments			19,700
Convertible bridge loan	800
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			14,000
Convertible bridge loan	500
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			13,000
Convertible bridge loan	300
Sonobi
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments			$ 9,200
Convertible bridge loan	$ 200