Net Income (Loss) per Share - Calculations of Net Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Basic and Diluted:
Income (loss) from continuing operations	$ (15,282)	$ (14,209)	$ (30,047)	$ (24,407)
Income (loss) from discontinued operations	0	1,315	0	1,363
Net income (loss) attributable to Actua Corporation	$ (15,282)	$ (12,894)	$ (30,047)	$ (23,044)
Income (loss) from continuing operations per share (usd per share)	$ (0.41)	$ (0.38)	$ (0.81)	$ (0.66)
Income (loss) from discontinued operations per share (usd per share)	0.00	0.03	0.00	0.04
Net income (loss) attributable to Actua Corporation per share (usd per share)	$ (0.41)	$ (0.35)	$ (0.81)	$ (0.62)
Shares used in computation of basic and diluted income (loss) per share	37,123	37,313	36,983	37,205