Consolidated Businesses - Pro Forma Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
FolioDynamix, Ludwig, NuCivic, Textizen and KMI
Business Acquisition [Line Items]
Revenue	$ 133,921	$ 114,380
Net income (loss) from continuing operations attributable to Actua Corporation	$ (95,496)	$ (41,579)
Net income (loss) from continuing operations per diluted share attributable to Actua Corporation (in dollars per share)	$ (2.58)	$ (1.12)
Folio Dynamix, NuCivic, KMI, Ludwig, and Superior Access
Business Acquisition [Line Items]
Revenue		$ 113,705	$ 90,561
Net income (loss) from continuing operations attributable to Actua Corporation		$ (41,295)	$ (35,439)
Net income (loss) from continuing operations per diluted share attributable to Actua Corporation (in dollars per share)		$ (1.11)	$ (0.97)