Debt	3 Months Ended
Mar. 31, 2021
Debt Disclosure [Abstract]
Debt	8. Convertible Notes The Company issued unsecured convertible notes with an aggregate principal amount of $1.7 million in 2020. Previously, the Company issued unsecured convertible notes with aggregate principal amounts of $0.9 million and $1.3 million and in 2019 and 2018, respectively. The notes accrued interest at a rate of 5% per year and mature in December 2021, unless earlier converted. No principal or interest was payable prior to maturity as the convertible notes and any accrued interest would automatically convert upon a qualified financing event at a conversion price equal to 85% of the price per share of the qualified financing. Holders may have also elected to convert their notes to shares of common stock upon the maturity of the notes at the then fair value of common stock. If the Company experienced a change in control, holders may have either converted the outstanding principal amount plus any accrued interest into shares of common stock at the then fair value of common stock or may have required the Company to repurchase the notes in cash at a price equal to 200% of the outstanding principal amount plus any accrued interest. Certain conversion and redemption features as described above were determined to be an embedded derivative requiring bifurcation and separate accounting in accordance with ASC 815, Derivatives and Hedging. The fair value of the embedded derivative was determined using a discounted cash flow simulation methodology that assigns probabilities to the timing and likelihood of each event. The discount rate was determined based on market interest rate data for securities with similar durations and credit ratings to the convertible notes. The fair value of the embedded derivative was recorded as a liability with an offsetting amount recorded as a discount on the convertible notes at each issuance. The discount is being amortized to interest expense using the effective interest method over the contractual term of the notes. In May 2020, the outstanding principal balance of the convertible notes of $3.8 million and accrued interest of $160,000 converted into 512,858 shares of Series B-1 convertible preferred stock. The excess of the carrying value of the convertible notes and the derivative liability over the fair value of the Series B-1 convertible preferred stock at conversion resulted in a gain upon extinguishment of $199,000.

Debt

3 Months Ended

Mar. 31, 2021

8. Convertible Notes

The Company issued unsecured convertible notes with an aggregate principal amount of $1.7 million in 2020. Previously, the Company issued unsecured convertible notes with aggregate principal amounts of $0.9 million and $1.3 million and in 2019 and 2018, respectively. The notes accrued interest at a rate of 5% per year and mature in December 2021, unless earlier converted. No principal or interest was payable prior to maturity as the convertible notes and any accrued interest would automatically convert upon a qualified financing event at a conversion price equal to 85% of the price per share of the qualified financing. Holders may have also elected to convert their notes to shares of common stock upon the maturity of the notes at the then fair value of common stock. If the Company experienced a change in control, holders may have either converted the outstanding principal amount plus any accrued interest into shares of common stock at the then fair value of common stock or may have required the Company to repurchase the notes in cash at a price equal to 200% of the outstanding principal amount plus any accrued interest.

Certain conversion and redemption features as described above were determined to be an embedded derivative requiring bifurcation and separate accounting in accordance with ASC 815, Derivatives and Hedging. The fair value of the embedded derivative was determined using a discounted cash flow simulation methodology that assigns probabilities to the timing and likelihood of each event. The discount rate was determined based on market interest rate data for securities with similar durations and credit ratings to the convertible notes. The fair value of the embedded derivative was recorded as a liability with an offsetting amount recorded as a discount on the convertible notes at each issuance. The discount is being amortized to interest expense using the effective interest method over the contractual term of the notes.

In May 2020, the outstanding principal balance of the convertible notes of $3.8 million and accrued interest of $160,000 converted into 512,858 shares of Series B-1 convertible preferred stock.

The excess of the carrying value of the convertible notes and the derivative liability over the fair value of the Series B-1 convertible preferred stock at conversion resulted in a gain upon extinguishment of $199,000.