Stockholders' Equity Common Stock - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Number of shares, Beginning Balance	5,026,246
Number of shares, Granted	992,625
Number of shares, Exercised	(136,685)
Number of shares, Ending Balance	5,882,186	5,026,246
Number of shares, Options exercisable	1,892,915
Number of shares, Options vested and expected to vest	5,756,568
Weighted Average Exercise Price, Beginning Balance	$ 8.01
Weighted Average Exercise Price, Granted	27.52
Weighted Average Exercise Price, Exercised	1.15
Weighted Average Exercise Price, Ending Balance	11.46	$ 8.01
Weighted Average Exercise Price, Options exercisable	2.66
Weighted Average Exercise Price, Options vested and expected to vest	$ 11.34
Weighted Average Remaining Contractual Term, Outstanding	8 years 8 months 5 days	8 years 8 months 12 days
Weighted Average Remaining Contractual Term, Options exercisable	8 years 18 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	8 years 8 months 1 day
Aggregate Intrinsic Value	$ 93,314	$ 136,945
Aggregate Intrinsic Value, Options exercisable	45,250
Aggregate Intrinsic Value, Options vested and expected to vest	$ 91,974