Term Loan (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended				3 Months Ended	9 Months Ended
	Sep. 30, 2018	Aug. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Debt instrument tranche amount funded	$ 15,500				$ 15,500	$ 15,500
Amortization of the debt discount (recovery) expense						156
Interest expense					678	1,037
Increase in warrants issued				36,008
Warrants outstanding to purchase common stock							0
Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Fair value of warrant	$ 247				$ 247	$ 247
Warrants outstanding to purchase common stock	86,419				86,419	86,419
Warrants exercise price per common share	$ 2.43				$ 2.43	$ 2.43
Warrant exercisable term						10 years
Number of shares issued for cashless exercise	72,325
Loan Agreement [Member] | Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Debt instrument, agreement date				2017-12
Loan Agreement [Member] | Silicon Valley Bank [Member] | Modification [Member]
Debt Instrument [Line Items]
Debt instrument, agreement date			2018-06
Loan Agreement [Member] | Silicon Valley Bank [Member] | Initial Tranche [Member]
Debt Instrument [Line Items]
Debt instrument tranche amount funded				$ 7,000
Loan Agreement [Member] | Silicon Valley Bank [Member] | Initial Tranche [Member] | Modification [Member]
Debt Instrument [Line Items]
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
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
Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument tranche amount funded	$ 15,500				$ 15,500	$ 15,500
Aggregate principal amount of debt instrument		$ 15,500
Repayment of outstanding borrowings of loan agreement		12,000
Repayment of final payment fee		$ 485
Interest expense					678	1,037
Final payment fee						1,008
Term Loan [Member] | Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Amortization of the debt discount (recovery) expense					$ (8)	$ 156
Debt instrument, frequency periodic payment, interest						monthly
Term Loan [Member] | Silicon Valley Bank [Member] | Loan Agreement [Member]
Debt Instrument [Line Items]
Debt instrument, interest only payment end date		Mar. 31, 2020
Debt instrument principal repayment period		30 months
Debt instrument, maturity date		Sep. 01, 2022
Debt instrument, payment commencing period		2018-09
Debt instrument, final payment fee percentage		6.50%
Debt instrument prepayment fee		$ 295
Debt instrument default interest payment above normal interest rate		5.00%
Warrants exercise price per common share		$ 9.79
Warrant exercisable term		10 years
Warrants outstanding to purchase common stock		40,000
Term Loan [Member] | Silicon Valley Bank [Member] | Loan Agreement [Member] | Prior to First Anniversary [Member]
Debt Instrument [Line Items]
Debt instrument, prepayment fee payable on outstanding principal, in percentage		3.00%
Term Loan [Member] | Silicon Valley Bank [Member] | Loan Agreement [Member] | After First Anniversary, but Prior to Second Anniversary [Member]
Debt Instrument [Line Items]
Debt instrument, prepayment fee payable on outstanding principal, in percentage		2.00%
Term Loan [Member] | Silicon Valley Bank [Member] | Loan Agreement [Member] | After Second Anniversary [Member]
Debt Instrument [Line Items]
Debt instrument, prepayment fee payable on outstanding principal, in percentage		1.00%
Term Loan [Member] | Silicon Valley Bank [Member] | Loan Agreement [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Debt instrument, floating interest rate		0.50%
Term Loan [Member] | Silicon Valley Bank [Member] | Initial Tranche [Member]
Debt Instrument [Line Items]
Effective interest rate on initial tranche of debt instrument	9.29%			9.25%	9.29%	9.29%