Equity-Based Compensation - Total aggregate fair value of restricted stock and shares surrendered by Actua's employees (Detail) - Restricted stock - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock vested in period, fair value	$ 1,145	$ 8,548	$ 776	$ 5,243	$ 9,693	$ 6,019
Shares paid for tax withholding for share based payments (in shares)	736	211,560	736	191,898	212,296	192,634