Acquisitions of Ownership Interests in Partner Companies and Funds (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired		$ 15,101	$ 52,431	$ 70,186
Equity method investments		108,089	154,666
Proceeds from sale of business		16,604	73,965	$ 25,058
Prognos [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired		$ 1,000
Equity method investments			$ 11,600
Ownership interest under equity method, percentage		28.70%	35.20%	34.50%
CloudMine [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan			$ 600
Acquisitions of ownership interests in companies and funds, net of cash acquired		$ 4,500
Equity method investments			$ 5,500	$ 4,900
Ownership interest under equity method, percentage		47.30%	30.10%	30.10%
Hoopla Software, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan		$ 300	$ 1,000
Equity method investments			$ 4,800	$ 3,800
Ownership interest under equity method, percentage		25.50%	25.50%	25.60%
Zipnosis [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired				$ 7,000
Ownership interest under equity method, percentage		25.40%	25.40%	26.30%
WebLinc [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan		$ 2,000
Acquisitions of ownership interests in companies and funds, net of cash acquired			$ 5,400
Equity method investments			$ 12,000	$ 6,600
Ownership interest under equity method, percentage		38.00%	38.00%	29.20%
Cask Data [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan		$ 2,000
Acquisitions of ownership interests in companies and funds, net of cash acquired				$ 11,000
Equity method investments			$ 11,000
Ownership interest under equity method, percentage		31.20%	31.30%	34.20%
Appfirst [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan			$ 1,200
Equity method investments				$ 11,600
Proceeds from sale of business	$ 900
Apprenda [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired				$ 10,000
Equity method investments					$ 12,100
Ownership interest under equity method, percentage		29.30%	29.40%	29.50%
InfoBionic [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan		$ 5,300
Acquisitions of ownership interests in companies and funds, net of cash acquired			$ 5,000
Equity method investments			$ 14,500	$ 9,500
Ownership interest under equity method, percentage		39.50%	39.70%	38.50%
Quantia [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan				$ 2,800
Equity method investments					12,500
Pneuron [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired				3,500
Equity method investments		$ 0			5,000
Clutch [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired			$ 4,000
Equity method investments				$ 12,300
Ownership interest under equity method, percentage		42.70%	42.80%	39.30%
Sonobi [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan		$ 3,800
Acquisitions of ownership interests in companies and funds, net of cash acquired				$ 5,400
Equity method investments			$ 5,400
Ownership interest under equity method, percentage		21.60%	21.60%	22.60%
Advantedge [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan				$ 1,000
Equity method investments					$ 15,300
meQuilibrium [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan			$ 1,500
Acquisitions of ownership interests in companies and funds, net of cash acquired		$ 2,500
Equity method investments			$ 8,000	$ 6,500
Ownership interest under equity method, percentage		36.20%	31.50%	31.50%
Spongecell [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan		$ 600	$ 4,000
Equity method investments		$ 6,000	$ 18,000	$ 14,000
Ownership interest under equity method, percentage		23.00%	23.00%	23.00%
Dabo [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan				$ 300
Payments to Acquire Other Investments				2,000
Aventura [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan		$ 300	$ 300
Equity method investments		$ 0	6,200	$ 6,000
BrickWork [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired			$ 4,200
Ownership interest under equity method, percentage		20.30%	20.30%	20.30%
QuanticMind, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan			$ 2,800
Acquisitions of ownership interests in companies and funds, net of cash acquired		$ 1,800
Equity method investments			$ 9,700	$ 7,000
Ownership interest under equity method, percentage		24.70%	23.20%	23.60%
Aktana, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired	$ 5,500	$ 1,500	$ 2,700
Equity method investments			$ 8,200
Ownership interest under equity method, percentage	23.40%	24.50%	31.20%
Moxe Health [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired			$ 4,500
Ownership interest under equity method, percentage		32.40%	32.40%	32.60%
Full Measure [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired		$ 3,100	$ 4,600
Equity method investments		0	8,600	$ 4,000
Trice [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan			1,900
Acquisitions of ownership interests in companies and funds, net of cash acquired		$ 2,100
Equity method investments			$ 8,000	$ 6,100
Ownership interest under equity method, percentage		24.80%	27.60%	27.70%
Propeller [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired			$ 5,000
Equity method investments				$ 9,000
Ownership interest under equity method, percentage		24.00%	24.00%	24.60%
Transactis [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired			$ 5,000
Equity method investments				$ 9,500
Ownership interest under equity method, percentage		23.80%	24.20%	24.50%
Syapse, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired		$ 2,300	$ 7,500
Equity method investments			$ 13,300	$ 5,800
Ownership interest under equity method, percentage		20.10%	26.20%	24.40%
Lumesis, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan		$ 200	$ 700
Equity method investments			$ 6,200	$ 5,600
Ownership interest under equity method, percentage		43.80%	44.10%	44.70%
T-REX Group, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Acquisitions of ownership interests in companies and funds, net of cash acquired			$ 6,000
Ownership interest under equity method, percentage		21.10%	23.60%	23.60%
NovaSom, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan		$ 2,000	$ 1,000
Equity method investments			$ 22,100	$ 21,000
Ownership interest under equity method, percentage		31.70%	31.70%	31.70%
Good Start Genetics Inc [Member]
Schedule of Equity Method Investments [Line Items]
Convertible bridge loan		$ 1,800	$ 5,200
Equity method investments			$ 17,200	$ 12,000