Summary of Selected Information Related to Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenue	$ 30,592		$ 18,422
Net income (loss) attributable to Actua Corporation	(14,765)		(10,150)
Assets	513,025				529,098
Operating Segments
Segment Reporting Information [Line Items]
Revenue	30,592		18,422
Net income (loss) attributable to Actua Corporation	(7,947)		(4,614)
Assets	444,016				434,180
Vertical Cloud | Operating Segments
Segment Reporting Information [Line Items]
Revenue	30,592		18,422
Net income (loss) attributable to Actua Corporation	(7,947)		(4,614)
Assets	427,399				418,063
Vertical Cloud Venture | Operating Segments
Segment Reporting Information [Line Items]
Assets	16,617				16,117
Dispositions
Segment Reporting Information [Line Items]
Assets	2,989				2,998
Dispositions | Reconciling Items
Segment Reporting Information [Line Items]
Net income (loss) attributable to Actua Corporation			(264)
Other
Segment Reporting Information [Line Items]
Net income (loss) attributable to Actua Corporation	(6,818)		(5,272)
Assets	66,020				91,920
Other | Reconciling Items
Segment Reporting Information [Line Items]
Net income (loss) attributable to Actua Corporation	$ (6,818)	[1]	$ (5,272)	[1]

[1] The following table reflects the components of Net income (loss) attributable to Actua Corporation included in Other (in thousands):