Share-Based Payments - Stock Award Activity (Detail) (2007 Stock Incentive Plan [Member], USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
2007 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Stock Options Outstanding, Beginning Balance	3,145,544
Number of Stock Options Outstanding, Granted	613,600
Number of Stock Options Outstanding, Exercised	(57,985)
Number of Stock Options Outstanding, Forfeited	(44,014)
Number of Stock Options Outstanding, Ending Balance	3,657,145	3,145,544
Number of Stock Options, Exercisable	2,130,507
Number of Stock Options, Vested and expected to vest	2,887,672
Weighted- Average Exercise Price Outstanding, Beginning Balance	$ 0.88
Weighted-Average Exercise Price, Granted	$ 9.05
Weighted-Average Exercise Price, Exercised	$ 0.70
Weighted-Average Exercise Price, Forfeited	$ 2.08
Weighted-Average Exercise Price Outstanding, Ending Balance	$ 2.24	$ 0.88
Weighted-Average Exercise Price, Exercisable	$ 0.57
Weighted-Average Exercise Price, Vested and expected to vest	$ 1.33
Weighted-Average Remaining Contractual Term Outstanding, Beginning Balance	7 years 7 months 24 days	7 years 8 months 19 days
Weighted-Average Remaining Contractual Term, Exercisable	6 years 9 months
Weighted-Average Remaining Contractual Term, Vested and expected to vest	7 years 2 months 23 days
Aggregate Intrinsic Value Outstanding, Beginning Balance	$ 15,402
Aggregate Intrinsic Value Outstanding, Ending Balance	24,897	15,402
Aggregate Intrinsic Value, Exercisable	18,084
Aggregate Intrinsic Value, Vested and expected to vest	$ 22,299