CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenue	$ 133,421	$ 84,837	$ 59,201
Operating expenses
Cost of revenue	39,229	24,420	17,757
Sales and marketing	48,414	39,710	28,129
General and administrative	61,857	51,731	30,960
Research and development	29,168	15,408	9,032
Amortization of intangibles assets	15,251	10,532	8,470
Impairment related and other	41,238	1,187	4,292
Total operating expenses	235,157	142,988	98,640
Operating income (loss)	(101,736)	(58,151)	(39,439)
Other income (loss), net	1,692	5,300	(4,210)
Interest income	131	463	227
Interest expense	(203)	(1,613)	(1,484)
Income (loss) before income taxes, equity loss and noncontrolling interest	(100,116)	(54,001)	(44,906)
Income tax (expense) benefit	(229)	12,931	17,571
Equity loss	0	(776)	(2,963)
Income (loss) from continuing operations	(100,345)	(41,846)	(30,298)
Income (loss) from discontinued operations, including gain on sale, net of tax	0	14,026	232,339
Net income (loss)	(100,345)	(27,820)	202,041
Less: Net income (loss) attributable to the noncontrolling interest	(4,265)	(4,264)	(7,018)
Net income (loss) attributable to Actua Corporation	(96,080)	(23,556)	209,059
Amounts attributable to Actua Corporation:
Net income (loss) from continuing operations	(96,080)	(37,582)	(25,669)
Net income (loss) from discontinued operations	0	14,026	234,728
Net income (loss) attributable to Actua Corporation	$ (96,080)	$ (23,556)	$ 209,059
Basic and diluted income (loss) per share attributable to Actua Corporation:
Income (loss) from continuing operations (in dollars per share)	$ (2.59)	$ (1.01)	$ (0.70)
Income (loss) from discontinued operations (in dollars per share)	0.00	0.38	6.42
Net income (loss) attributable to Actua Corporation per share (in dollars per share)	$ (2.59)	$ (0.63)	$ 5.72
Shares used in computation of basic and diluted income (loss) per share (in shares)	37,080	37,130	36,536
Net income (loss)	$ (100,345)	$ (27,820)	$ 202,041
Other comprehensive income
Unrealized holding gain (loss) in marketable securities	0	0	24
Reclassified adjustments/realized net (gains) loss on marketable securities	0	0	(23)
Other accumulated other comprehensive income (loss)	0	0	(1)
Comprehensive income (loss)	(100,345)	(27,820)	202,041
Less: Comprehensive income (loss) attributable to noncontrolling interests	(4,265)	(4,264)	(7,018)
Comprehensive income (loss) attributable to Actua Corporation	$ (96,080)	$ (23,556)	$ 209,059