Stock-based Compensation - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	May 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value of options granted		$ 11.19	$ 5.79	$ 9.91	$ 3.84
Unrestricted stock awards granted	6,056
Options vested and expected to vest		6,103,326		6,103,326		6,663,152
Options vested and expected to vest, weighted average exercise price		$ 6.86		$ 6.86		$ 5.08
Options vested and expected to vest, weighted average contractual life				6 years 8 months 12 days		7 years 1 month 6 days
Options outstanding, aggregate intrinsic value		$ 153,200,000		$ 153,200,000
Options exercisable, aggregate intrinsic value		92,100,000		92,100,000
Aggregate intrinsic value of options exercised		18,500,000	192,000.0	22,500,000	280,000.0
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense		$ 12,400,000		$ 12,400,000
Unrecognized compensation expense expected to be recognized				3 years 18 days