Summary of Information Regarding Option Activity (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012
Options Outstanding
Options outstanding at January 1, 2013	2,315,090		2,629,490
Granted	388,052
Exercised	(786,254)
Forfeited/Cancelled	(121,300)
Options outstanding at June 30, 2013	1,795,588		2,629,490
Options exercisable at June 30, 2013	865,636
Vested and expected to vest at June 30, 2013	1,694,909	[1]
Weighted average exercise price per share
Options outstanding at January 1, 2013	$ 4.20		$ 4.08
Granted	$ 5.86
Exercised	$ 4.28
Forfeited/Cancelled	$ 4.28
Options outstanding at June 30, 2013	$ 4.53		$ 4.08
Options exercisable at June 30, 2013	$ 4.31
Vested and expected to vest at June 30, 2013	$ 4.48	[1]
Weighted average remaining contractual term (in years)
Options outstanding at June 30, 2013	7 years 1 month 21 days
Options exercisable at June 30, 2013	5 years 4 months 10 days
Vested and expected to vest at June 30, 2013	7 years 26 days	[1]
Aggregate intrinsic value
Options outstanding at June 30, 2013	$ 6,689,614
Options exercisable at June 30, 2013	3,405,885
Vested and expected to vest at June 30, 2013	$ 6,388,888	[1]

[1] This represents the number of vested options as of June 30, 2013 plus the number of unvested options expected to vest as of June 30, 2013 based on the unvested outstanding options at June 30, 2013 adjusted for estimated forfeiture rates of 8% for awards granted to non-executive level employees and 3% for awards granted to executive level employees.