Ownership Interests in and Advances to Partner Companies and Funds - Narrative (Detail) - USD ($)	1 Months Ended						3 Months Ended		9 Months Ended
	Jul. 31, 2016	Jun. 30, 2016	Apr. 30, 2016	Jan. 31, 2016	Jul. 31, 2015	Apr. 30, 2015	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Apr. 30, 2017	Dec. 31, 2015
Investment [Line Items]
Proceeds from sale of business									$ 73,854,000	$ 25,029,000
Equity method investments							$ 151,885,000		151,885,000			$ 151,840,000
Revenue									299,768,000	291,860,000
Gross profit									190,168,000	182,809,000
Net loss									(135,045,000)	(105,042,000)
AppFirst, Inc.
Investment [Line Items]
Proceeds from sale of business		$ 900,000
Asset Impairment Charges								$ 1,700,000
Equity method investments							0		0
Bridgevine Inc
Investment [Line Items]
Proceeds from sale of business		$ 5,000,000
Gain on sale of business									400,000
Putney, Inc.
Investment [Line Items]
Proceeds from sale of business	$ 400,000		$ 58,200,000
Gain on sale of business							400,000	$ 55,200,000
Quantia Inc.
Investment [Line Items]
Proceeds from sale of business	$ 600,000				$ 7,800,000
Gain on sale of business							600,000		600,000
Penn Mezzanine Assets
Investment [Line Items]
Asset Impairment Charges							2,400,000		2,400,000
Other Assets							200,000		200,000
Aventura
Investment [Line Items]
Asset Impairment Charges							1,000,000		1,000,000
Equity method investments							$ 2,700,000		2,700,000
Drive Factor
Investment [Line Items]
Proceeds from sale of business			1,100,000			$ 9,100,000
Gain on sale of business									1,100,000	$ 6,100,000
Thing Worx Inc
Investment [Line Items]
Proceeds from sale of business			$ 3,300,000	$ 4,100,000
Gain on sale of business									$ 3,300,000
Scenario, Forecast | Putney, Inc.
Investment [Line Items]
Amount held in escrow											$ 600,000