Stock-based Compensation - Schedule of Stock Options Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding at December 31, 2012, Number of Shares	1,554,200
Granted, Number of Shares	2,009,551
Exercised, Number of Shares	(3,195)
Cancelled, Number of Shares	(370,896)
Options outstanding at September 30, 2013, Number of Shares	3,189,660
Options exercisable at September 30, 2013, Number of Shares	975,669
Options outstanding at December 31, 2012, Weighted Average Exercise Price	$ 1.3890
Granted, Weighted Average Exercise Price	$ 3.1121
Exercised, Weighted Average Exercise Price	$ 0.3722
Cancelled, Weighted Average Exercise Price	$ 1.3844
Options outstanding at September 30, 2013, Weighted Average Exercise Price	$ 2.1634
Options exercisable at September 30, 2013, Weighted Average Exercise Price	$ 0.5911
Options outstanding at December 31, 2012, Aggregate Intrinsic Value	$ 2,348
Options outstanding at September 30, 2013, Aggregate Intrinsic Value	24,996
Options exercisable at September 30, 2013, Aggregate Intrinsic Value	$ 9,180