Net Loss per Share - Calculations of Net Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Basic and Diluted:
Net loss attributable to Actua Corporation	$ (14,331)	$ (14,765)
Net income (loss) attributable to Actua Corporation per share (usd per share)	$ (0.38)	$ (0.40)
Shares used in computation of basic and diluted loss per share (in shares)	37,293	36,842