Segment Information - Summary of Selected Information Related to Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenue	$ 33,536	$ 19,029	$ 64,128	$ 37,451
Net income (loss) attributable to Actua Corporation	(15,282)	(12,894)	(30,047)	(23,044)
Income tax benefit (expense)	1	(599)	178	(505)
Net loss attributable to the noncontrolling interest	761	1,475	1,921	2,379
Assets	504,842		504,842		$ 528,912
Operating Segments
Segment Reporting Information [Line Items]
Revenue	33,536	19,029	64,128	37,451
Net income (loss) attributable to Actua Corporation	(7,144)	(6,332)	(15,091)	(11,258)
Assets	440,531		440,531		433,994
Impairment Related And Other [Member]
Segment Reporting Information [Line Items]
Net income (loss) attributable to Actua Corporation	(106)	(763)	(201)	(763)
Vertical Cloud | Operating Segments
Segment Reporting Information [Line Items]
Revenue	33,536	19,029	64,128	37,451
Net income (loss) attributable to Actua Corporation	(7,144)	(6,012)	(15,091)	(10,626)
Assets	423,914		423,914		417,877
Vertical Cloud Venture | Operating Segments
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Net income (loss) attributable to Actua Corporation	0	(320)	0	(632)
Assets	16,617		16,617		16,117
Dispositions
Segment Reporting Information [Line Items]
Assets	0		0		2,998
Dispositions | Reconciling Items
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Net income (loss) attributable to Actua Corporation	0	1,315	0	1,363
Other
Segment Reporting Information [Line Items]
Net income (loss) attributable to Actua Corporation	(8,138)	(7,877)	(14,956)	(13,149)
Assets	64,311		64,311		$ 91,920
Other | Reconciling Items
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Net income (loss) attributable to Actua Corporation	(8,138)	(7,877)	(14,956)	(13,149)
Corporate Other Income Loss [Member]
Segment Reporting Information [Line Items]
Net income (loss) attributable to Actua Corporation	(1)	653	1,389	947
Noncontrolling Interest Income Loss [Member]
Segment Reporting Information [Line Items]
Net loss attributable to the noncontrolling interest	761	1,475	1,921	2,379
General and administrative
Segment Reporting Information [Line Items]
Net income (loss) attributable to Actua Corporation	(8,816)	(9,375)	(18,107)	(15,926)
Interest income
Segment Reporting Information [Line Items]
Net income (loss) attributable to Actua Corporation	24	133	42	$ 214
Income tax benefit (expense)	$ 0	$ 0	$ 0