Segment Information - Summary of Selected Information Related to Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenue	$ 27,937	$ 24,917	$ 79,977	$ 72,957
Net loss attributable to Actua Corporation	(10,074)	(13,882)	(37,146)	(43,929)
Segment Reporting Information, Profit (Loss) [Abstract]
General and administrative	(11,228)	(12,542)	(34,926)	(40,889)
Impairment related and other	(45)	(285)	(393)	(982)
Other income, net	2,831	96	2,726	1,537
Interest income	31	30	118	83
Net income attributable to the noncontrolling interest	(1,019)	(751)	(2,888)	(2,672)
Net loss attributable to Actua Corporation	(10,074)	(13,882)	(37,146)	(43,929)
Assets	420,782		420,782		$ 450,144
Operating Segments
Segment Reporting Information [Line Items]
Revenue	27,937	24,917	79,977	72,957
Net loss attributable to Actua Corporation	(4,871)	(4,192)	(16,896)	(14,769)
Segment Reporting Information, Profit (Loss) [Abstract]
Net loss attributable to Actua Corporation	(4,871)	(4,192)	(16,896)	(14,769)
Assets	358,542		358,542		365,582
Operating Segments | Vertical Cloud
Segment Reporting Information [Line Items]
Revenue	27,937	24,917	79,977	72,957
Net loss attributable to Actua Corporation	(4,871)	(4,192)	(16,896)	(14,769)
Segment Reporting Information, Profit (Loss) [Abstract]
Net loss attributable to Actua Corporation	(4,871)	(4,192)	(16,896)	(14,769)
Assets	341,293		341,293		347,436
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	17,249		17,249		18,146
Dispositions
Segment Reporting Information [Line Items]
Net loss attributable to Actua Corporation	(3,607)	(2,150)	(7,556)	(6,539)
Segment Reporting Information, Profit (Loss) [Abstract]
Net loss attributable to Actua Corporation	(3,607)	(2,150)	(7,556)	(6,539)
Assets	33,609		33,609		29,129
Other
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Net loss attributable to Actua Corporation	(1,596)	(7,540)	(12,694)	(22,621)
Segment Reporting Information, Profit (Loss) [Abstract]
General and administrative	(5,249)	(8,045)	(18,074)	(25,965)
Impairment related and other	3	(89)	(42)	(290)
Other income, net	2,842	(1)	2,888	1,388
Interest income	24	25	92	67
Net income attributable to the noncontrolling interest	784	570	2,442	2,179
Net loss attributable to Actua Corporation	(1,596)	(7,540)	(12,694)	(22,621)
Assets	28,631		28,631		$ 55,433
GovDelivery
Segment Reporting Information [Line Items]
Revenue	$ 11,400	$ 9,200	$ 30,600	$ 25,300