Segment Information - Summary of Selected Information Related to Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenue	$ 36,709	$ 33,536	$ 71,319	$ 64,128
Net loss attributable to Actua Corporation	(12,741)	(15,282)	(27,072)	(30,047)
Segment Reporting Information, Profit (Loss) [Abstract]
General and administrative	(13,561)	(15,966)	(28,057)	(31,402)
Impairment related and other	(117)	(489)	(348)	(835)
Other (loss) income, net	(67)	(102)	(223)	1,435
Interest income	39	35	87	54
Net loss attributable to the noncontrolling interest	817	761	1,869	1,921
Net loss attributable to Actua Corporation	(12,741)	(15,282)	(27,072)	(30,047)
Assets	417,006		417,006		$ 450,144
Operating Segments
Segment Reporting Information [Line Items]
Revenue	36,709	33,536	71,319	64,128
Net loss attributable to Actua Corporation	(7,726)	(7,428)	(16,247)	(15,632)
Segment Reporting Information, Profit (Loss) [Abstract]
Net loss attributable to Actua Corporation	(7,726)	(7,428)	(16,247)	(15,632)
Assets	386,714		386,714		393,182
Operating Segments | Vertical Cloud
Segment Reporting Information [Line Items]
Revenue	36,709	33,536	71,319	64,128
Net loss attributable to Actua Corporation	(7,726)	(7,428)	(16,247)	(15,632)
Segment Reporting Information, Profit (Loss) [Abstract]
Net loss attributable to Actua Corporation	(7,726)	(7,428)	(16,247)	(15,632)
Assets	369,597		369,597		376,565
Operating Segments | Vertical Cloud (Venture)
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Net loss attributable to Actua Corporation	0	0	0	0
Segment Reporting Information, Profit (Loss) [Abstract]
Net loss attributable to Actua Corporation	0	0	0	0
Assets	17,117		17,117		16,617
Other
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Net loss attributable to Actua Corporation	(5,015)	(7,854)	(10,825)	(14,415)
Segment Reporting Information, Profit (Loss) [Abstract]
General and administrative	(5,818)	(8,532)	(12,763)	(17,566)
Impairment related and other	(45)	(106)	(45)	(201)
Other (loss) income, net	0	(1)	46	1,389
Interest income	31	24	68	42
Net loss attributable to the noncontrolling interest	817	761	1,869	1,921
Net loss attributable to Actua Corporation	(5,015)	$ (7,854)	(10,825)	$ (14,415)
Assets	$ 30,292		$ 30,292		$ 56,962