Stock Option Activity and Related Information (Detail) (USD $)	0 Months Ended		3 Months Ended		6 Months Ended			0 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2014 Employee Stock Option [Member]
Exercisable Weighted Average Exercise Price per Share
Options vested and expected to vest			6,671,244		6,671,244		5,988,706
Options vested and expected to vest, weighted average exercise price			$ 11.36		$ 11.36		$ 7.67
Options vested and expected to vest, weighted average remaining contractual life	6 years 10 months 24 days	6 years 7 months 6 days
Options outstanding, aggregate intrinsic value			$ 101,800,000		$ 101,800,000
Options exercisable, aggregate intrinsic value			71,600,000		71,600,000
Total intrinsic value of options exercised			3,600,000	807,000	11,400,000	4,000,000
Unrecognized compensation expense								$ 23,400,000
Unrecognized compensation expense expected to be recognized, Weighted-average period								2 years 7 months 6 days