Segment Reporting - Active Partner Companies by Segment (Detail) - USD ($) $ in Millions	1 Months Ended
	Jul. 26, 2018	Sep. 30, 2018
Schedule of Equity Method Investments [Line Items]
Proceeds from sale of equity method investments	$ 55.0
BrickWork
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		20.30%
CloudMine
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		47.30%
Clutch Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		41.20%
Flashtalking
Schedule of Equity Method Investments [Line Items]
Ownership interest under cost method, percentage		10.30%
Hoopla Software, Inc.
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		25.50%
Lumesis, Inc.
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		43.80%
MediaMath, Inc.
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		13.30%
Percent of ownership sold	39.13%
Proceeds from sale of equity method investments	$ 45.0
Moxe Health
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		32.40%
Prognos
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		28.70%
QuanticMind, Inc.
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		24.70%
Sonobi
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		21.60%
T-REX Group, Inc.
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		21.10%
Transactis
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		23.70%
WebLinc
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		37.90%
Healthcare | Aktana, Inc.
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		20.10%
Healthcare | InfoBionic
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		25.40%
Healthcare | meQuilibrium
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		33.10%
Healthcare | Novasom, Inc.
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		31.70%
Healthcare | Propeller
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		19.60%
Healthcare | Syapse, Inc.
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		20.00%
Healthcare | Trice
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		23.40%
Healthcare | Zipnosis
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage		34.70%