Notes Payable	12 Months Ended
Dec. 31, 2017
Debt Disclosure [Abstract]
Notes Payable	Notes Payable On December 24, 2014, we entered into a Loan and Security Agreement, as amended from time to time, the Loan Agreement, with a bank and a financial institution whereby we may borrow up to $15.0 million in three separate draws of $5.0 million each. The Term A Loans, for an aggregate of $5.0 million, were drawn on December 24, 2014 and each bear a fixed rate of interest of 6.97%. In connection with the issuance of the Term A Loans, we issued detachable, fully vested warrants to purchase an aggregate of 41,208 shares of Series C Preferred Stock at an exercise price of $4.55 per share to the lenders. The grant-date fair value of the warrants of $0.1 million was recorded as a liability, with a reduction to the carrying value of the Term A Loans, and which is recognized as additional interest expense over the remaining term of the Loans. The initial fair value of the warrants was determined using the Black-Scholes option pricing model with the following assumptions: a stock price volatility of 70.2%, an expected life equal to the contractual term of the warrants of ten years and a risk-free interest rate of 1.97%. In January 2016, the Loan Agreement was amended to combine Term B Loans and Term C Loans for a total of $10.0 million available for draw through December 31, 2016 and delay the beginning of our Term A Loans’ principal repayments from February 1, 2016 until February 1, 2017. The Term B Loans and Term C Loans became available for draw on July 1, 2016. In December 2016, we further amended the Loan Agreement to (i) allow for the Term B Loans and Term C Loans to be drawn on December 30, 2016, (ii) delay principal repayments of all Term Loans until February 1, 2018 and (iii) amend the interest rate for each Term Loan. The Term B Loans and the Term C Loans were drawn on December 30, 2016. As of December 31, 2017, the Term Loans are due in one monthly interest-only payment through January 2018, followed by 24 equal monthly principal and interest payments beginning February 1, 2018, with final maturity in January 2020. Each Loan bears interest equal to the greater of 3-month U.S. LIBOR plus 6.37% or 7.3%. The interest rate was 7.86% as of December 31, 2017. In connection with the issuance of the Term B & C Loans, we issued detachable, fully vested warrants to purchase an aggregate of 82,416 shares of Series C Preferred Stock at an exercise price of $4.55 per share to the lenders. The grant-date fair value of the warrants of $0.9 million was recorded as a liability, with a reduction to the carrying value of the Term B & C Loans, and which is recognized as additional interest expense over the remaining term of the Loans. The initial fair value of the warrants was determined using the Black-Scholes option pricing model with the following assumptions: a stock price volatility of 79.2%, an expected life equal to the contractual term of the warrants of ten years and a risk-free interest rate of 2.45%. As discussed in Note 7 below, all of the outstanding warrants to purchase shares of preferred stock automatically converted into warrants to purchase shares of common stock in connection with the IPO and are accounted for as equity from the conversion date forward. All warrants related to Term Loans were exercised during the year ended December 31, 2017. As of December 31, 2017, the carrying amount of the Term Loans was $14.4 million, which is net of discounts of $0.6 million and of which $6.9 million is classified as current liabilities as of December 31, 2017. The effective interest rate on the Term Loans at December 31, 2017 was 12.25%. As of December 31, 2017, future principal maturities of the Term Loans were $6.9 million, $7.5 million and $0.6 million in 2018, 2019 and 2020, respectively. The Term Loans are secured by a first priority interest in most of our assets, excluding intellectual property. As of December 31, 2017, we were in compliance with the covenants contained in the Loan Agreement.

Notes Payable

On December 24, 2014, we entered into a Loan and Security Agreement, as amended from time to time, the Loan Agreement, with a bank and a financial institution whereby we may borrow up to $15.0 million in three separate draws of $5.0 million each. The Term A Loans, for an aggregate of $5.0 million, were drawn on December 24, 2014 and each bear a fixed rate of interest of 6.97%.

In connection with the issuance of the Term A Loans, we issued detachable, fully vested warrants to purchase an aggregate of 41,208 shares of Series C Preferred Stock at an exercise price of $4.55 per share to the lenders. The grant-date fair value of the warrants of $0.1 million was recorded as a liability, with a reduction to the carrying value of the Term A Loans, and which is recognized as additional interest expense over the remaining term of the Loans. The initial fair value of the warrants was determined using the Black-Scholes option pricing model with the following assumptions: a stock price volatility of 70.2%, an expected life equal to the contractual term of the warrants of ten years and a risk-free interest rate of 1.97%.

In January 2016, the Loan Agreement was amended to combine Term B Loans and Term C Loans for a total of $10.0 million available for draw through December 31, 2016 and delay the beginning of our Term A Loans’ principal repayments from February 1, 2016 until February 1, 2017. The Term B Loans and Term C Loans became available for draw on July 1, 2016. In December 2016, we further amended the Loan Agreement to (i) allow for the Term B Loans and Term C Loans to be drawn on December 30, 2016, (ii) delay principal repayments of all Term Loans until February 1, 2018 and (iii) amend the interest rate for each Term Loan. The Term B Loans and the Term C Loans were drawn on December 30, 2016. As of December 31, 2017, the Term Loans are due in one monthly interest-only payment through January 2018, followed by 24 equal monthly principal and interest payments beginning February 1, 2018, with final maturity in January 2020. Each Loan bears interest equal to the greater of 3-month U.S. LIBOR plus 6.37% or 7.3%. The interest rate was 7.86% as of December 31, 2017.

In connection with the issuance of the Term B & C Loans, we issued detachable, fully vested warrants to purchase an aggregate of 82,416 shares of Series C Preferred Stock at an exercise price of $4.55 per share to the lenders. The grant-date fair value of the warrants of $0.9 million was recorded as a liability, with a reduction to the carrying value of the Term B & C Loans, and which is recognized as additional interest expense over the remaining term of the Loans. The initial fair value of the warrants was determined using the Black-Scholes option pricing model with the following assumptions: a stock price volatility of 79.2%, an expected life equal to the contractual term of the warrants of ten years and a risk-free interest rate of 2.45%. As discussed in Note 7 below, all of the outstanding warrants to purchase shares of preferred stock automatically converted into warrants to purchase shares of common stock in connection with the IPO and are accounted for as equity from the conversion date forward. All warrants related to Term Loans were exercised during the year ended December 31, 2017.

As of December 31, 2017, the carrying amount of the Term Loans was $14.4 million, which is net of discounts of $0.6 million and of which $6.9 million is classified as current liabilities as of December 31, 2017. The effective interest rate on the Term Loans at December 31, 2017 was 12.25%. As of December 31, 2017, future principal maturities of the Term Loans were $6.9 million, $7.5 million and $0.6 million in 2018, 2019 and 2020, respectively.

The Term Loans are secured by a first priority interest in most of our assets, excluding intellectual property. As of December 31, 2017, we were in compliance with the covenants contained in the Loan Agreement.