Summary of Selected Information Related to Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenue	$ 20,762	$ 16,071	$ 58,213	$ 41,521
Net income (loss) attributable to Actua Corporation	(10,680)	(3,332)	(33,724)	8,878
Assets	498,611		498,611		529,718
Operating Segments
Segment Reporting Information [Line Items]
Revenue	20,762	16,071	58,213	41,521
Net income (loss) attributable to Actua Corporation	(6,605)	(4,335)	(18,663)	(15,210)
Assets	206,689		206,689		195,680
Vertical Cloud | Operating Segments
Segment Reporting Information [Line Items]
Revenue	20,762	16,071	58,213	41,092
Net income (loss) attributable to Actua Corporation	(6,461)	(3,941)	(17,887)	(13,327)
Assets	191,580		191,580		179,801
Vertical Cloud Venture | Operating Segments
Segment Reporting Information [Line Items]
Revenue				429
Net income (loss) attributable to Actua Corporation	(144)	(394)	(776)	(1,883)
Assets	15,109		15,109		15,879
Dispositions
Segment Reporting Information [Line Items]
Net income (loss) attributable to Actua Corporation	2,426	5,079	3,789	34,695
Other
Segment Reporting Information [Line Items]
Net income (loss) attributable to Actua Corporation	(6,501)	(4,076)	(18,850)	(10,607)
Assets	$ 291,922		$ 291,922		$ 334,038