Equity Incentive Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Shares Available for Grant, Beginning balance	7,255,050
Options Outstanding, Shares Available for Grant, Authorized	3,182,868
Options Outstanding, Shares Available for Grant, RSUs canceled	212,466
Options Outstanding, Shares Available for Grant, Granted	(3,861,900)
Options Outstanding, Shares Available for Grant, Canceled	802,723
Options Outstanding, Shares Available for Grant, Ending balance	7,591,207
Options Outstanding, Number of Shares Underlying Options, Beginning balance	8,986,010
Options Outstanding, Number of Shares Underlying Options, Granted	3,861,900
Options Outstanding, Number of Shares Underlying Options, Exercised	(254,481)
Options Outstanding, Number of Shares Underlying Options, Canceled	(802,723)
Options Outstanding, Number of Shares Underlying Options, Ending balance	11,790,706
Options Outstanding, Number of Shares Underlying Options, Options exercisable	5,676,204
Options Outstanding, Number of Shares Underlying Options, Options vested and expected to vest	11,685,590
Options Outstanding, Weighted-Average Exercise Price, Beginning balance	$ 7.54
Options Outstanding, Weighted-Average Exercise Price, Granted	3.93
Options Outstanding, Weighted-Average Exercise Price, Exercised	0.99
Options Outstanding, Weighted-Average Exercise Price, Canceled	10.33
Options Outstanding, Weighted-Average Exercise Price, Ending balance	6.31
Options Outstanding, Weighted-Average Exercise Price, Options exercisable	7.19
Options Outstanding, Weighted-Average Exercise Price, Options vested and expected to vest	$ 6.30
Options Outstanding, Aggregate Intrinsic Value, Balance	$ 9,675	$ 5,458
Options Outstanding, Aggregate Intrinsic Value, Options exercisable-March 31, 2019	9,295
Options Outstanding, Aggregate Intrinsic Value, Options vested and expected to vest-March 31, 2019	$ 9,671