CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Revenue	$ 31,189	$ 26,854	$ 61,696	$ 52,040
Operating expenses
Cost of revenue	7,884	7,288	15,678	14,010
Sales and marketing	9,763	10,461	19,670	20,580
General and administrative	11,786	11,372	24,718	23,698
Research and development	6,911	5,388	13,644	10,695
Amortization of intangible assets	4,333	3,626	7,996	7,208
Impairment related and other	310	117	670	348
Total operating expenses	40,987	38,252	82,376	76,539
Operating income (loss)	(9,798)	(11,398)	(20,680)	(24,499)
Other income (loss), net	2,558	(15)	3,425	(105)
Interest income	142	39	297	87
Interest expense	(44)	(33)	(71)	(66)
Income (loss) before income taxes and noncontrolling interests	(7,142)	(11,407)	(17,029)	(24,583)
Income tax benefit (expense)	(184)	(72)	(449)	(198)
Income (loss) from continuing operations	(7,326)	(11,479)	(17,478)	(24,781)
Income (loss) from discontinued operations, net of tax	0	(2,079)	0	(4,160)
Net income (loss)	(7,326)	(13,558)	(17,478)	(28,941)
Less: Net income (loss) attributable to the noncontrolling interests	(463)	(817)	(945)	(1,869)
Net income (loss) attributable to Actua Corporation	(6,863)	(12,741)	(16,533)	(27,072)
Amounts attributable to Actua Corporation:
Net income (loss) from continuing operations	(6,863)	(10,763)	(16,533)	(23,123)
Net income (loss) from discontinued operations	0	(1,978)	0	(3,949)
Net income (loss) attributable to Actua Corporation	$ (6,863)	$ (12,741)	$ (16,533)	$ (27,072)
Basic and diluted income (loss) per share attributable to Actua Corporation:
Income (loss) from continuing operations (in dollars per share)	$ (0.22)	$ (0.30)	$ (0.52)	$ (0.62)
Income (loss) from discontinued operations (in dollars per share)	0.00	(0.05)	0.00	(0.11)
Net income (loss) (in dollars per share)	$ (0.22)	$ (0.35)	$ (0.52)	$ (0.73)
Shares used in computation of basic and diluted income (loss) per share (in shares)	31,267	36,760	31,687	37,027
Net income (loss)	$ (7,326)	$ (13,558)	$ (17,478)	$ (28,941)
Other comprehensive income (loss):
Foreign currency translation adjustment	(34)	(38)	(46)	(112)
Comprehensive income (loss)	(7,360)	(13,596)	(17,524)	(29,053)
Less: Comprehensive income (loss) attributable to the noncontrolling interests	(463)	(817)	(945)	(1,869)
Comprehensive income (loss) attributable to Actua Corporation	$ (6,897)	$ (12,779)	$ (16,579)	$ (27,184)