Operating Segments - Active Partner Companies by Segment (Detail)	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Advantedge Healthcare Solutions Inc [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	40.10%	40.10%		40.10%
Aktana, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	24.50%	31.20%	23.40%
Apprenda [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	29.30%	29.40%		29.50%
BrickWork [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	20.30%	20.30%		20.30%
Cask Data [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	31.20%	31.30%		34.20%
CloudMine [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	47.30%	30.10%		30.10%
Clutch [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	42.70%	42.80%		39.30%
Hoopla Software, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	25.50%	25.50%		25.60%
InfoBionic [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	39.50%	39.70%		38.50%
Lumesis, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	43.80%	44.10%		44.70%
MediaMath, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	20.50%	20.50%		20.60%
meQuilibrium [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	36.20%	31.50%		31.50%
Moxe Health [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	32.40%	32.40%		32.60%
NovaSom, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	31.70%	31.70%		31.70%
Prognos [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	28.70%	35.20%		34.50%
Propeller [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	24.00%	24.00%		24.60%
QuanticMind, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	24.70%	23.20%		23.60%
Sonobi [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	21.60%	21.60%		22.60%
Spongecell [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	23.00%	23.00%		23.00%
Syapse, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	20.10%	26.20%		24.40%
T-REX Group, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	21.10%	23.60%		23.60%
Transactis [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	23.80%	24.20%		24.50%
Trice [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	24.80%	27.60%		27.70%
WebLinc [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	38.00%	38.00%		29.20%
Zipnosis [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest under equity method, percentage	25.40%	25.40%		26.30%