Convertible Promissory Notes	9 Months Ended
Sep. 30, 2020
Debt Disclosure [Abstract]
Convertible Promissory Notes	5. Convertible Promissory Notes Frazier Convertible Note Financing From January 2018 to April 2019, the Company issued convertible promissory notes to Frazier (the “Frazier Notes”) for an aggregate of $2.4 million and bearing interest at per annum rates ranging from 1.68% to 2.55%. Of the Frazier Notes, $1.9 million were issued in 2018 and $0.5 million were issued in April 2019. Due to certain embedded features within the Frazier Notes, the Company elected to account for these notes and all their embedded features under the fair value option. The Company recorded changes in the fair value of the Frazier Notes in the statements of operations until May 2019, when the Frazier Notes and related accrued interest were exchanged, at their then fair value of $2.4 million, for the convertible promissory notes issued by the Company in May 2019 (the “May 2019 Notes”). For the nine months ended September 30, 2019, the Company recognized $50,000 of other income in the statements of operations related to decreases in the fair value of the Frazier Notes. For the nine months ended September 30, 2019, the Company recognized $15,000 of interest expense in connection with the Frazier Notes. No interest expense or changes in fair value related to the Frazier Notes were recorded in the three months ended September 30, 2019, as the Frazier Notes were exchanged in May 2019. The Company did not have any such expenses incurred for the three and nine months ended September 30, 2020 in connection with the Frazier Notes. May 2019 Convertible Note Financing In May 2019, the Company entered into a note purchase agreement under which it issued the unsecured May 2019 Notes for an aggregate of $90.3 million, resulting in gross proceeds to the Company of $87.8 million in cash and $2.4 million related to the exchange of the Frazier Notes and related accrued interest for the May 2019 Notes. Including the conversion of the Frazier Notes, Frazier purchased $20.0 million of the May 2019 Notes. The May 2019 Notes bore interest at a rate of 6% per annum and were subordinated to borrowings under the Company’s loan and security agreement (see Note 7). Due to certain embedded features within the May 2019 Notes, the Company elected to account for these notes and all their embedded features under the fair value option. The outstanding principal and accrued interest of the May 2019 Notes automatically converted into 6,107,918 shares of common stock immediately prior to the completion of the IPO on October 29, 2019.

Convertible Promissory Notes

9 Months Ended

Sep. 30, 2020

5. Convertible Promissory Notes

Frazier Convertible Note Financing

From January 2018 to April 2019, the Company issued convertible promissory notes to Frazier (the “Frazier Notes”) for an aggregate of $2.4 million and bearing interest at per annum rates ranging from 1.68% to 2.55%. Of the Frazier Notes, $1.9 million were issued in 2018 and $0.5 million were issued in April 2019. Due to certain embedded features within the Frazier Notes, the Company elected to account for these notes and all their embedded features under the fair value option. The Company recorded changes in the fair value of the Frazier Notes in the statements of operations until May 2019, when the Frazier Notes and related accrued interest were exchanged, at their then fair value of $2.4 million, for the convertible promissory notes issued by the Company in May 2019 (the “May 2019 Notes”). For the nine months ended September 30, 2019, the Company recognized $50,000 of other income in the statements of operations related to decreases in the fair value of the Frazier Notes. For the nine months ended September 30, 2019, the Company recognized $15,000 of interest expense in connection with the Frazier Notes. No interest expense or changes in fair value related to the Frazier Notes were recorded in the three months ended September 30, 2019, as the Frazier Notes were exchanged in May 2019. The Company did not have any such expenses incurred for the three and nine months ended September 30, 2020 in connection with the Frazier Notes.

May 2019 Convertible Note Financing

In May 2019, the Company entered into a note purchase agreement under which it issued the unsecured May 2019 Notes for an aggregate of $90.3 million, resulting in gross proceeds to the Company of $87.8 million in cash and $2.4 million related to the exchange of the Frazier Notes and related accrued interest for the May 2019 Notes. Including the conversion of the Frazier Notes, Frazier purchased $20.0 million of the May 2019 Notes. The May 2019 Notes bore interest at a rate of 6% per annum and were subordinated to borrowings under the Company’s loan and security agreement (see Note 7).

Due to certain embedded features within the May 2019 Notes, the Company elected to account for these notes and all their embedded features under the fair value option. The outstanding principal and accrued interest of the May 2019 Notes automatically converted into 6,107,918 shares of common stock immediately prior to the completion of the IPO on October 29, 2019.