Stockholders' Equity - Summary of the Company's Stock Options (Detail) (Employee Stock Option [Member], USD $)	6 Months Ended
	Jun. 30, 2013
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options, Options outstanding, beginning of period	6,321,076
Number of options, Granted
Number of options, Exercised	(902,314)
Number of options, Expired / forfeited	(127,124)
Number of options, Options outstanding, end of period	5,291,638
Number of options, Options exercisable, end of period	4,747,679
Number of options, Options expected to vest, end of period	467,065
Weighted average exercise price, Options outstanding, beginning of period	$ 6.05
Weighted average exercise price, Granted
Weighted average exercise price, Exercised	$ 4.48
Weighted average exercise price, Expired / forfeited	$ 5.78
Weighted average exercise price, Options outstanding, end of period	$ 6.32
Weighted average exercise price, Options exercisable, end of period	$ 6.52
Weighted average exercise price, Options expected to vest, end of period	$ 4.61
Weighted Average Remaining Contractual Life (years), Options outstanding, end of period	4 years 3 months 18 days
Weighted Average Remaining Contractual Life (years), Options exercisable, end of period	4 years 11 days
Weighted Average Remaining Contractual Life (years), Options expected to vest, end of period	6 years 7 months 21 days
Aggregate intrinsic value, Options outstanding, end of period	$ 13,573,609
Aggregate intrinsic value, Options exercisable, end of period	11,450,150
Aggregate intrinsic value, Options expected to vest, end of period	$ 1,826,751