Stock Based Awards - Summary of Stock Options Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Shares Available for Grant
Shares Available for Grant, Beginning balance	9,533	168,571
Shares Available for Grant, Additional shares authorized	2,531,915	803,590
Shares Available for Grant, Options granted	(1,471,142)	(974,459)
Shares Available for Grant, Restricted stock units granted	(185,514)
Shares Available for Grant, Options cancelled	106,609	11,831
Shares Available for Grant, Ending balance	991,401	9,533
Number of shares
Number of Shares, Beginning balance	1,403,655	462,471
Number of Shares, Options granted	1,471,142	974,459
Number of Shares, Options exercised	(44,822)	(21,444)
Number of Shares, Options cancelled	(106,609)	(11,831)
Number of Shares, Ending balance	2,723,366	1,403,655
Number of Shares, Vested and expected to vest	2,651,182
Number of Shares, Exercisable	648,058
Weighted Average Exercise Price
Weighted Average Exercise Price, Beginning balance	$ 1.90	$ 1.31
Weighted Average Exercise Price, Options granted	$ 18.68	$ 2.16
Weighted Average Exercise Price, Options exercised	$ 1.32	$ 1.27
Weighted Average Exercise Price, Options cancelled	$ 18.43	$ 1.30
Weighted Average Exercise Price, Ending balance	$ 10.33	$ 1.90
Weighted Average Exercise Price, Vested and expected to vest	$ 10.27
Weighted Average Exercise Price, Exercisable	$ 3.04
Weighted Average Remaining Contractual Life (in years)
Weighted Average Remaining Contractual Life, Options outstanding	8 years 9 months 18 days
Weighted Average Remaining Contractual Life, Vested and expected to vest	8 years 9 months 18 days
Weighted Average Remaining Contractual Life, Exercisable	7 years 8 months 12 days
Aggregate Intrinsic Value, Options outstanding	$ 36,006
Aggregate Intrinsic Value, Vested and expected to vest	35,141
Aggregate Intrinsic Value, Exercisable	$ 12,858