CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Revenue	$ 109,301	$ 98,432	$ 57,129
Operating expenses
Cost of revenue	29,186	27,420	16,299
Sales and marketing	40,807	35,832	28,556
General and administrative	46,936	54,516	47,031
Research and development	21,642	18,996	8,023
Amortization of intangibles assets	14,384	13,449	8,950
Impairment related and other	768	40,769	1,114
Total operating expenses	153,723	190,982	109,973
Operating income (loss)	(44,422)	(92,550)	(52,844)
Other income (loss), net	2,857	1,741	5,359
Interest income	283	126	455
Interest expense	(96)	(197)	(1,604)
Income (loss) from continuing operations before income taxes, equity loss and noncontrolling interests	(41,378)	(90,880)	(48,634)
Income tax benefit (expense)	13,210	(293)	10,528
Equity income (loss)	0	0	(776)
Income (loss) from continuing operations	(28,168)	(91,173)	(38,882)
Income (loss) from discontinued operations, including gain on sale, net of tax	94,017	(9,172)	11,062
Net income (loss)	65,849	(100,345)	(27,820)
Less: Net income (loss) attributable to the noncontrolling interests	(4,236)	(4,265)	(4,264)
Net income (loss) attributable to Actua Corporation	70,085	(96,080)	(23,556)
Amounts attributable to Actua Corporation:
Net loss from continuing operations	(25,210)	(87,560)	(34,872)
Net income (loss) from discontinued operations	95,295	(8,520)	11,316
Net income (loss) attributable to Actua Corporation	$ 70,085	$ (96,080)	$ (23,556)
Basic and diluted income (loss) per share attributable to Actua Corporation:
Loss from continuing operations (in dollars per share)	$ (0.69)	$ (2.36)	$ (0.94)
Income (loss) from discontinued operations (in dollars per share)	2.60	(0.23)	0.31
Net income (loss) (in dollars per share)	$ 1.91	$ (2.59)	$ (0.63)
Shares used in computation of basic and diluted income (loss) per share (in shares)	36,672	37,080	37,130
Net income (loss)	$ 65,849	$ (100,345)	$ (27,820)
Other comprehensive income (loss)
Foreign currency translation adjustment	(59)	0	0
Comprehensive income (loss)	65,790	(100,345)	(27,820)
Less: Comprehensive income (loss) attributable to noncontrolling interests	(4,236)	(4,265)	(4,264)
Comprehensive income (loss) attributable to Actua Corporation	$ 70,026	$ (96,080)	$ (23,556)