Term Loan (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended	6 Months Ended
	Aug. 03, 2018	Jun. 12, 2018	Dec. 31, 2017	Jun. 30, 2018	Jun. 30, 2018
Debt Instrument [Line Items]
Debt instrument tranche amount funded				$ 12,000	$ 12,000
Amortization of the debt discount					164
Interest expense				200	359
Increase in warrants issued			36,008
Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Fair value of warrant				$ 247	$ 247
Warrants outstanding to purchase common stock				86,419	86,419
Warrants exercise price per common share				$ 2.43	$ 2.43
Warrant exercisable term					10 years
Loan Agreement [Member] | Silicon Valley Bank [Member] | Modification [Member]
Debt Instrument [Line Items]
Debt instrument, agreement date		Jun. 12, 2018
Loan Agreement [Member] | Silicon Valley Bank [Member] | Second Tranche [Member] | Modification [Member]
Debt Instrument [Line Items]
Debt instrument tranche amount funded		$ 5,000
Debt instrument, interest only payment end date		Sep. 30, 2018
Debt instrument principal repayment period		24 months
Debt instrument principal repayment period on achievement of certain clinical milestones		18 months
Debt instrument, maturity date		Sep. 30, 2020
Loan Agreement [Member] | Silicon Valley Bank [Member] | Initial Tranche [Member] | Modification [Member]
Debt Instrument [Line Items]
Debt instrument tranche amount funded		$ 7,000
Debt instrument principal repayment period		30 months
Debt instrument principal repayment period on achievement of certain clinical milestones		24 months
Debt instrument, maturity date		Mar. 31, 2021
Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument tranche amount funded				$ 12,000	$ 12,000
Interest expense				200	359
Final payment fee					780
Term Loan [Member] | Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Amortization of the debt discount				$ 92	$ 164
Debt instrument, frequency periodic payment, interest					monthly
Term Loan [Member] | Silicon Valley Bank [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Debt instrument, agreement date	Aug. 03, 2018
Aggregate principal amount of debt instrument	$ 15,500
Modified interest period start Date	Sep. 30, 2018
Modified interest period end date	Mar. 31, 2020
Term Loan [Member] | Silicon Valley Bank [Member] | Initial Tranche [Member]
Debt Instrument [Line Items]
Effective interest rate on initial tranche of debt instrument			9.25%	10.24%	10.24%