Stock-Based Compensation Expense - Summary of Stock Option Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Outstanding, Beginning Balance	1,110,744	755,074	893,039
Number of Options, Granted	766,882	865,516	170,269
Number of Options, Assumed	551,363
Number of Options, Exercised	(38,570)		(20,161)
Number of Options, Canceled	(20,572)	(509,846)	(288,073)
Number of Options, Outstanding, Ending Balance	2,369,847	1,110,744	755,074	893,039
Number of Options, Vested and expected to vest	2,309,228
Number of Options, Vested and exercisable	1,155,771
Weighted Average Exercise Price Per Share, Outstanding, Beginning Balance	$ 4.59	$ 3.30	$ 3.29
Weighted Average Exercise Price Per Share, Granted	15.04	4.94	3.51
Weighted Average Exercise Price Per Share, Assumed	30.11
Weighted Average Exercise Price Per Share, Exercised	4.20		3.14
Weighted Average Exercise Price Per Share, Canceled	28.09	3.27	3.40
Weighted Average Exercise Price Per Share, Outstanding, Ending Balance	13.99	$ 4.59	$ 3.30	$ 3.29
Weighted Average Exercise Price Per Share, Vested and expected to vest	14.05
Weighted Average Exercise Price Per Share, Vested and Exercisable	$ 17.11
Weighted Average Contractual Term, Outstanding	8 years 3 months 11 days	8 years 8 months 19 days	7 years 7 months 13 days	8 years 1 month 10 days
Weighted Average Contractual Term, Vested and Expected to Vest	8 years 3 months 4 days
Weighted Average Contractual Term, Vested and Exercisable	7 years 6 months 7 days
Weighted-average grant date fair value of Stock Options Outstanding, Granted	$ 11.60	$ 4.02	$ 1.37