Stockholders' Equity (Deficit) Common Stock - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Number of shares, Beginning Balance	3,579,342
Number of shares, Granted	1,750,124
Number of shares, Exercised	(232,970)
Number of shares, Forfeited	(70,250)
Number of shares, Ending Balance	5,026,246	3,579,342
Number of shares, Options vested and expected to vest	5,026,246
Number of shares, Options exercisable	1,643,955
Weighted Average Exercise Price, Beginning Balance	$ 1.38
Weighted Average Exercise Price, Granted	20.44
Weighted Average Exercise Price, Exercised	0.40
Weighted Average Exercise Price, Forfeited	5.04
Weighted Average Exercise Price, Ending Balance	8.01	$ 1.38
Weighted Average Exercise Price, Options vested and expected to vest	8.01
Weighted Average Exercise Price, Options exercisable	$ 1.33
Weighted Average Remaining Contractual Term, Outstanding	8 years 8 months 12 days	9 years 2 months 16 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	8 years 8 months 12 days
Weighted Average Remaining Contractual Term, Options exercisable	8 years 1 month 17 days
Aggregate Intrinsic Value	$ 136,945	$ 59,498
Aggregate Intrinsic Value, Options vested and expected to vest	136,945
Aggregate Intrinsic Value, Options exercisable	$ 55,507