CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Revenue	$ 30,507	$ 25,186
Operating expenses
Cost of revenue	7,794	6,722
Sales and marketing	9,907	10,119
General and administrative	12,932	12,326
Research and development	6,733	5,307
Amortization of intangible assets	3,663	3,582
Impairment related and other	360	231
Total operating expenses	41,389	38,287
Operating income (loss)	(10,882)	(13,101)
Other income (loss), net	867	(90)
Interest income	155	48
Interest expense	(27)	(33)
Income (loss) before income taxes and noncontrolling interests	(9,887)	(13,176)
Income tax benefit (expense)	(265)	(126)
Income (loss) from continuing operations	(10,152)	(13,302)
Income (loss) from discontinued operations, net of tax	0	(2,081)
Net income (loss)	(10,152)	(15,383)
Less: Net income (loss) attributable to the noncontrolling interests	(482)	(1,052)
Net income (loss) attributable to Actua Corporation	(9,670)	(14,331)
Amounts attributable to Actua Corporation:
Net income (loss) from continuing operations	(9,670)	(12,360)
Net income (loss) from discontinued operations	0	(1,971)
Net income (loss) attributable to Actua Corporation	$ (9,670)	$ (14,331)
Basic and diluted income (loss) per share attributable to Actua Corporation:
Income (loss) from continuing operations (in dollars per share)	$ (0.30)	$ (0.33)
Income (loss) from discontinued operations (in dollars per share)	0.00	(0.05)
Net income (loss) (in dollars per share)	$ (0.30)	$ (0.38)
Shares used in computation of basic and diluted income (loss) per share (in shares)	32,113	37,293
Net income (loss)	$ (10,152)	$ (15,383)
Other comprehensive income (loss):
Foreign currency translation adjustment	(12)	(74)
Comprehensive income (loss)	(10,164)	(15,457)
Less: Comprehensive income (loss) attributable to the noncontrolling interests	(482)	(1,052)
Comprehensive income (loss) attributable to Actua Corporation	$ (9,682)	$ (14,405)