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						9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock vested in period, fair value	$ 168	$ 776	$ 5,243	$ 399	$ 875	$ 10,839	$ 6,187	$ 12,113
Shares paid for tax withholding for share based payments (in shares)	2,727	736	191,898	3,330	26,032	207,649	195,361	237,011