Issued And Unvested Shares Of Restricted Stock Granted (Detail)	3 Months Ended
	Mar. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Unvested	3,508,624
First Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Unvested	1,714,366
Vesting Conditions	Subject to certain market conditions, as discussed below
Second Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Unvested	503,315
Vesting Conditions	Subject to certain performance conditions, as discussed below
Third Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Unvested	1,157,035
Vesting Conditions	25% each year for four years on the anniversary of the grant date
Fourth Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Unvested	91,666
Vesting Conditions	50% in each of May 2015 and November 2015
Fifth Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Unvested	24,042
Vesting Conditions	One-third in each of September 2015, March 2016 and September 2016
Sixth Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Unvested	18,200
Vesting Conditions	100% in July 2015 (granted to Actua's Board of Directors, see subsection below)