Stock based Compensation - Stock Option Activity (Detail) - Stock Options - USD ($) $ / shares in Units, $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Options Outstanding
Outstanding at beginning of period	6,132,641
Granted	685,690
Exercised	(590,479)
Forfeited and cancelled	(303,135)
Outstanding at end of period	5,924,717	6,132,641
Exercisable at end of period	3,695,958
Vested and expected to vest end of the period	5,892,328
Weighted average exercise price
Outstanding at beginning of period	$ 11.62
Granted	16.27
Exercised	4.24
Forfeited and cancelled	15.98
Outstanding at end of period	12.67	$ 11.62
Exercisable at end of period	9.42
Vested and expected to vest end of the period	$ 12.63
Weighted Average outstanding at the end of the period	6 years 2 months 16 days	6 years 2 months 1 day
Weighted average exercisable contractual term end of the period	4 years 11 months 27 days
Weighted average vested and expected to vest contractual term end of the period	6 years 2 months 12 days
Aggregate intrinsic value outstanding	$ 57.8	$ 50.4
Aggregate intrinsic value exercisable at the end of the period	46.3
Aggregate intrinsic value vested and expected to vest at the end of the period	$ 57.6
Options Exercisable
Outstanding at end of period	3,695,958