Equity Incentive Plans - Summary of Activity Under 2008 Plan, 2014 Plan and Inducement Plan Including Grants to Nonemployees Issued (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity Incentive Plans
Shares Available for Grant, Beginning balance	608,528
Shares Available for Grant, Options authorized	2,490,417
Shares Available for Grant, Options granted	(2,362,685)
Shares Available for Grant, Options exercised	0
Shares Available for Grant, Options canceled	528,615
Issuance of common stock for services and restricted stock units, net of forfeitures	(45,007)
Shares Available for Grant, Issuance of common stock for services	(113,136)	(75,183)	(46,858)
Shares Available for Grant, Ending balance	1,196,746	608,528
Options Issued and Outstanding Number of Shares, Beginning balance	5,506,760
Options Issued and Outstanding Number of Shares, Options authorized	0
Options Issued and Outstanding Number of Shares, Options granted	2,362,685
Options Issued and Outstanding Number of Shares, Options exercised	(68,062)
Options Issued and Outstanding Number, Options canceled	(528,615)
Options Issued and Outstanding Number of Shares, Issuance of common stock for services	0
Options Issued and Outstanding Number of Shares, Ending balance	7,272,768	5,506,760
Options Issued and Outstanding Average Exercise Price per Share, Beginning balance	$ 8.32
Options Issued and Outstanding Number of Shares, Expected to vest	6,754,711
Options Issued and Outstanding Number of Shares, Exercisable	4,183,281
Options Issued and Outstanding Average Exercise Price per Share, Options granted	$ 2.56
Options Issued and Outstanding Average Exercise Price per Share, Options exercised	2.59
Options Issued and Outstanding Average Exercise Price per Share, Options canceled	7.69
Options Issued and Outstanding Average Exercise Price per Share, Issuance of common stock for services	0
Options Issued and Outstanding Average Exercise Price per Share, Ending balance	6.55	$ 8.32
Options Issued and Outstanding Average Exercise Price per Share, Expected to vest	6.74
Options Issued and Outstanding Average Exercise Price per Share, Exercisable	$ 7.95
Weighted Average Remaining Contractual Term, Ending Balance	7 years 4 months 24 days
Weighted Average Remaining Contractual Term, Vested and Expected to Vest	7 years 3 months 18 days
Weighted Average Remaining Contractual Term, Exercisable	6 years 5 months 16 days
Aggregate Intrinsic Value, Ending balance	$ 19,128
Aggregate Intrinsic Value, Expected to Vest	17,217
Aggregate Intrinsic Value, Exercisable	$ 8,753