Pro Forma Information (Detail) (USD $)	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Revenue	$ 21,100	$ 18,300	$ 60,800	$ 51,200
Net income (loss) from continuing operations attributable to Actua Corporation	$ (13,100)	$ (8,000)	$ (37,400)	$ (28,300)
Net income (loss) from continuing operations per diluted share attributable to Actua Corporation	$ (0.35)	$ (0.22)	$ (1.00)	$ (0.77)

The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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