Treasury Stock	12 Months Ended
Dec. 31, 2017
Equity [Abstract]
Treasury Stock	Treasury Stock Actua has been authorized pursuant to a share repurchase program to repurchase, from time to time, shares of common stock in open market transactions, including pursuant to trading plans meeting the requirements of Rule 10b5-1 under the Exchange Act, in privately negotiated transactions or pursuant to one or more issuer tender offers. The program was adopted in 2008 and expanded in 2013 to allow for the repurchase of up to $150.0 million of shares of Actua's common stock. During the year ended December 31, 2016, the program was further expanded to allow for an additional $39.8 million of repurchases, increasing the total repurchase amount to $189.8 million, of which $30.5 million is available as of March 28, 2018. During the year ended December 31, 2017, Actua repurchased 2,175,268 shares of its common stock, paying $30.4 million for the shares at an average stock price of $13.95 per share. During the year ended December 31, 2016, Actua repurchased 5,598,094 shares of its common stock at an average stock price of $13.17 per share. Since commencement of the program through March 28, 2018, Actua has deployed a total of $159.3 million, excluding commissions and fees, to repurchase a total of 13,761,211 shares of common stock for an average purchase price of $11.58 per share. Repurchases are reflected in the line item "Treasury stock, at cost" as a reduction of stockholders’ equity in Actua’s Consolidated Balance Sheets in the relevant period. Actua does not expect to repurchase additional shares under the share repurchase plan.

Treasury Stock

Actua has been authorized pursuant to a share repurchase program to repurchase, from time to time, shares of common stock in open market transactions, including pursuant to trading plans meeting the requirements of Rule 10b5-1 under the Exchange Act, in privately negotiated transactions or pursuant to one or more issuer tender offers. The program was adopted in 2008 and expanded in 2013 to allow for the repurchase of up to $150.0 million of shares of Actua's common stock. During the year ended December 31, 2016, the program was further expanded to allow for an additional $39.8 million of repurchases, increasing the total repurchase amount to $189.8 million, of which $30.5 million is available as of March 28, 2018. During the year ended December 31, 2017, Actua repurchased 2,175,268 shares of its common stock, paying $30.4 million for the shares at an average stock price of $13.95 per share. During the year ended December 31, 2016, Actua repurchased 5,598,094 shares of its common stock at an average stock price of $13.17 per share. Since commencement of the program through March 28, 2018, Actua has deployed a total of $159.3 million, excluding commissions and fees, to repurchase a total of 13,761,211 shares of common stock for an average purchase price of $11.58 per share. Repurchases are reflected in the line item "Treasury stock, at cost" as a reduction of stockholders’ equity in Actua’s Consolidated Balance Sheets in the relevant period. Actua does not expect to repurchase additional shares under the share repurchase plan.