Calculations of Net Income (Loss) Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Basic and Diluted:
Income (loss) from continuing operations	$ (13,106)	$ (8,022)	$ (37,513)	$ (28,473)
Income (loss) from discontinued operations	2,426	4,690	3,789	37,351
Net income (loss) attributable to Actua Corporation	$ (10,680)	$ (3,332)	$ (33,724)	$ 8,878
Income (loss) from continuing operations per share	$ (0.35)	$ (0.22)	$ (1.01)	$ (0.78)
Income (loss) from discontinued operations per share	$ 0.06	$ 0.13	$ 0.10	$ 1.02
Net income (loss) attributable to Actua Corporation per share	$ (0.29)	$ (0.09)	$ (0.91)	$ 0.24
Shares used in computation of basis and diluted income (loss) per share	37,335	36,303	37,248	36,494