Convertible Promissory Notes	9 Months Ended
Sep. 30, 2019
Debt Disclosure [Abstract]
Convertible Promissory Notes	4. Convertible Promissory Notes Frazier Convertible Note Financing From January 2018 to April 2019, the Company issued 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 combined 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 May 2019 Notes. For the three and nine months ended September 30, 2018, and the nine months ended September 30, 2019, the Company recognized $18,000 of expense, $22,000 of expense, and $50,000 of income, respectively, in change in fair value of convertible promissory notes in the combined statements of operations related to changes in the fair value of the Frazier Notes. For the three and nine months ended September 30, 2018 and the nine months ended September 30, 2019, the Company recognized $4,000, $8,000 and $15,000, respectively, 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. May 2019 Convertible Note Financing In May 7, 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 bear interest at a rate of 6% per annum and are subordinated to borrowings under the Company’s loan and security agreement (see Note 5). The May 2019 Notes become payable upon demand of the holders of at least 60% of the outstanding principal amount of the May 2019 Notes, including Frazier, on May 7, 2020 (the “Maturity Date”), and become due and payable on May 7, 2022, subject to earlier conversion or repayment in the event the Company completes certain equity financings or a change of control. The May 2019 Notes can be converted/redeemed as follows (i) automatically converted upon a qualified equity financing, with a conversion price of the lesser of 80% of the price paid per share in such financing or the conversion cap price per share, (ii) optionally converted upon a non-qualified equity financing with a conversion price of 80% of the price paid per share in such financing, (iii) optionally converted any time after the Maturity Date, with a conversion price per share of the conversion cap price per share, (iv) automatically upon an IPO with a conversion price per share of the lesser of 80% of the IPO price per share, or the conversion cap price per share, and (v) upon certain corporate transactions, receive cash equal to the greater of (A) two times the then outstanding principal and accrued interest and (B) an amount equal to the amount that would be received as if the May 2019 Notes were converted with a conversion price of the conversion cap price per share. The conversion cap price per share is defined as $500.0 million less the outstanding principal and accrued interest divided by the total of (1) the total number of common shares outstanding immediately prior to conversion, (2) the number of common shares issuable upon exercise or conversion of exercisable or convertible securities, and (3) the number of shares of capital stock reserved for issuance under the Company’s equity incentive plan. The note purchase agreement includes, among others, covenants related to delivery of certain financial reports, certain registration rights, voting provisions regarding the composition of the Company’s board of directors, and limitations on the Company’s ability to pay dividends, incur additional indebtedness or consummate certain changes of control. The note purchase agreement also contains customary events of default, including bankruptcy, the failure to make payments when due, and certain material adverse changes. Upon the occurrence of an event of default, subject to any specified cure periods, all amounts owed by the Company may be declared immediately due and payable. As of September 30, 2019, the Company was in compliance with all applicable covenants under the note purchase agreement. 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. For the three and nine months ended September 30, 2019, the Company recognized $2.5 million and $4.9 million respectively, of other expense in the combined statements of operations related to increases in the fair value of the May 2019 Notes. For the three and nine months ended September 30, 2019, the Company recognized $1.4 million and $2.2 million, respectively, of interest expense in connection with the May 2019 Notes. As of September 30, 2019, the outstanding principal and accrued interest on the May 2019 Notes was $90.3 million and $2.2 million, respectively. The principal and accrued interest of the May 2019 Notes automatically converted upon the IPO on October 29, 2019, converting into 6,107,918 shares of common stock; refer to Note 7 for further information.

Convertible Promissory Notes

9 Months Ended

Sep. 30, 2019

4. Convertible Promissory Notes

Frazier Convertible Note Financing

From January 2018 to April 2019, the Company issued 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 combined 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 May 2019 Notes. For the three and nine months ended September 30, 2018, and the nine months ended September 30, 2019, the Company recognized $18,000 of expense, $22,000 of expense, and $50,000 of income, respectively, in change in fair value of convertible promissory notes in the combined statements of operations related to changes in the fair value of the Frazier Notes. For the three and nine months ended September 30, 2018 and the nine months ended September 30, 2019, the Company recognized $4,000, $8,000 and $15,000, respectively, 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.

May 2019 Convertible Note Financing

In May 7, 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 bear interest at a rate of 6% per annum and are subordinated to borrowings under the Company’s loan and security agreement (see Note 5). The May 2019 Notes become payable upon demand of the holders of at least 60% of the outstanding principal amount of the May 2019 Notes, including Frazier, on May 7, 2020 (the “Maturity Date”), and become due and payable on May 7, 2022, subject to earlier conversion or repayment in the event the Company completes certain equity financings or a change of control. The May 2019 Notes can be converted/redeemed as follows (i) automatically converted upon a qualified equity financing, with a conversion price of the lesser of 80% of the price paid per share in such financing or the conversion cap price per share, (ii) optionally converted upon a non-qualified equity financing with a conversion price of 80% of the price paid per share in such financing, (iii) optionally converted any time after the Maturity Date, with a conversion price per share of the conversion cap price per share, (iv) automatically upon an IPO with a conversion price per share of the lesser of 80% of the IPO price per share, or the conversion cap price per share, and (v) upon certain corporate transactions, receive cash equal to the greater of (A) two times the then outstanding principal and accrued interest and (B) an amount equal to the amount that would be received as if the May 2019 Notes were converted with a conversion price of the conversion cap price per share. The conversion cap price per share is defined as $500.0 million less the outstanding principal and accrued interest divided by the total of (1) the total number of common shares outstanding immediately prior to conversion, (2) the number of common shares issuable upon exercise or conversion of exercisable or convertible securities, and (3) the number of shares of capital stock reserved for issuance under the Company’s equity incentive plan.

The note purchase agreement includes, among others, covenants related to delivery of certain financial reports, certain registration rights, voting provisions regarding the composition of the Company’s board of directors, and limitations on the Company’s ability to pay dividends, incur additional indebtedness or consummate certain changes of control. The note purchase agreement also contains customary events of default, including bankruptcy, the failure to make payments when due, and certain material adverse changes. Upon the occurrence of an event of default, subject to any specified cure periods, all amounts owed by the Company may be declared immediately due and payable. As of September 30, 2019, the Company was in compliance with all applicable covenants under the note purchase agreement.

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. For the three and nine months ended September 30, 2019, the Company recognized $2.5 million and $4.9 million respectively, of other expense in the combined statements of operations related to increases in the fair value of the May 2019 Notes. For the three and nine months ended September 30, 2019, the Company recognized $1.4 million and $2.2 million, respectively, of interest expense in connection with the May 2019 Notes. As of September 30, 2019, the outstanding principal and accrued interest on the May 2019 Notes was $90.3 million and $2.2 million, respectively. The principal and accrued interest of the May 2019 Notes automatically converted upon the IPO on October 29, 2019, converting into 6,107,918 shares of common stock; refer to Note 7 for further information.