Ownership Interests in and Advances to Partner Companies and Funds - Narrative (Detail) - USD ($) $ in Thousands	1 Months Ended						3 Months Ended		6 Months Ended
	Apr. 30, 2017	Mar. 31, 2017	Jan. 31, 2017	Jul. 31, 2016	Apr. 30, 2016	Jul. 31, 2015	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2017	Jun. 30, 2016	Mar. 03, 2017	Dec. 31, 2016
Investment [Line Items]
Proceeds from sale of business									$ 16,462	$ 72,824
Equity method investments							$ 118,958		118,958			$ 154,666
Pneuron
Investment [Line Items]
Asset Impairment Charges							2,200	$ 2,700
Equity method investments							0		0
Putney Inc [Member]
Investment [Line Items]
Proceeds from sale of business	$ 700				$ 58,600
Gain on sale of business									700
Beyond.com, Inc
Investment [Line Items]
Consideration received per transaction		$ 26,000
Proceeds from sale of business		$ 15,500
Term of note receivable (in years)		3 years
Amount of consideration received		$ 10,500
Interest rate on note receivable											9.50%
Gain on sale of business							100
Quantia, Inc.
Investment [Line Items]
Proceeds from sale of business			$ 600	$ 600		$ 7,800
Gain on sale of business									600
Thing Worx, Inc.
Investment [Line Items]
Proceeds from sale of business					$ 3,300
Gain on sale of business										$ 3,300
Spongecell Inc.
Investment [Line Items]
Asset Impairment Charges							3,600
Equity method investments							$ 7,800		$ 7,800