Subsequent Events	6 Months Ended
Jun. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	12. Subsequent Events (a) Acquisition of intellectual property In July 2020, the Company entered into an intellectual property asset purchase agreement with Alexion pursuant to which Alexion sold and assigned to the Company Alexion’s right, title and interest in and to specified patent rights and other specified assets solely related to ENPP1. The Company issued 8,294,360 shares of its Series A-2 Convertible Preferred Stock to Alexion in consideration for the sale and assignment to the Company of such assets, with an estimated fair value of $17.8 million. The Company will expense the assets acquired from Alexion as of the acquisition date because the Company will use them in research and development activities and believes they have no alternative future uses. (b) Increase in Authorized Series A-2 Convertible Preferred Stock On July 17, 2020, the Company increased the number of authorized shares of Series A-2 Convertible Preferred Stock from 47,132,862 to 55,427,222. (c) Increase in Authorized Common Stock On July 17, 2020, the Company increased the number of authorized shares of common stock from 129,000,000 to 138,000,000. (d) 2020 Stock Incentive Plan On July 17, 2020, the Company’s stockholders approved the 2020 Stock Incentive Plan (the “2020 Plan”), which became effective on July 23, 2020. The 2020 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. The number of shares of the Company’s common stock reserved for issuance under the 2020 Plan is 1,588,315 shares; plus the shares of common stock remaining available for issuance under the 2017 Plan as of July 23, 2020. The number of shares reserved shall be annually increased on January 1, 2021 and each January 1 thereafter through January 1, 2030 by the lower of (i) 4% of the number of shares of common stock outstanding on the first day of such fiscal year and (ii) an amount determined by the Company’s board of directors. The shares of the Company’s common stock subject to outstanding awards under the 2017 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right will be added back to the shares of common stock available for issuance under the 2020 Plan. No more than 1,588,315 shares of the Company’s common stock may be granted subject to incentive stock options under the 2020 Plan. (e) 2020 Employee Stock Purchase Plan On July 17, 2020, the Company’s stockholders approved the 2020 Employee Stock Purchase Plan (the “ESPP”), which became effective on July 23, 2020. The ESPP initially provides participating employees with the opportunity to purchase up to an aggregate of 198,539 shares of the Company’s common stock. The number of shares of common stock reserved for issuance under the ESPP will automatically increase on January 1, 2021 and each January 1 thereafter through January 1, 2031, in an amount equal to the lowest of (1) 397,079 shares of the Company’s common stock, (2) 1% of the number of shares of the Company’s common stock outstanding on the first day of such fiscal year and (3) an amount determined by the Company’s board of directors. (f) Automatic Conversion Waiver and Reverse Stock Split On July 17, 2020, the Company eliminated the per share and gross proceeds thresholds for a firm-commitment underwritten public offering that triggers the automatic conversion of all outstanding shares of preferred stock into common stock. In addition, on July 17, 2020, the Company effected a one-for-7.4730 reverse stock split of the Company’s common stock. All share and per share amounts in the consolidated financial statements and notes thereto have been retroactively adjusted for all periods presented to give effect to this reverse stock split, including reclassifying an amount equal to the reduction in par value of common stock to additional paid-in capital. Shares of common stock underlying outstanding stock options and other equity instruments were proportionately reduced and the respective exercise prices, if applicable, were proportionately increased in accordance with the terms of the appropriate securities agreements. Shares of common stock reserved for issuance upon the conversion of the Company’s convertible preferred stock were proportionately reduced and the respective conversion prices were proportionately increased. Stockholders entitled to fractional shares as a result of the reverse stock split will receive a cash payment in lieu of receiving fractional shares. (g) Initial Public Offering On July 28, 2020, the Company completed an IPO pursuant to which it issued 7,000,000 shares of its common stock at a public ofering price of $16.00 per share, and on July 30, 2020, the Company sold an additional 1,050,000 shares pursuant to the exercise by the underwriters of their option to purchase additional shares. The Company received net proceeds from its IPO, inclusive of the exercise by the underwriters of their option to purchase additional shares, of approximately $116.5 million, after deducting underwriting discounts and commissions and estimated offering expenses. Upon the closing of the IPO, all 104,277,222 shares of the then outstanding preferred stock automatically converted into 13,953,850 shares of common stock. (h) Changes to Authorized Common Stock and Preferred Stock On July 28, 2020, the Company amended and restated its certificate of incorporation to authorize 200,000,000 shares of common stock and 5,000,000 shares of preferred stock, which shares of preferred stock are currently undesignated.

Subsequent Events

6 Months Ended

Jun. 30, 2020

12. Subsequent Events

(a) Acquisition of intellectual property

In July 2020, the Company entered into an intellectual property asset purchase agreement with Alexion pursuant to which Alexion sold and assigned to the Company Alexion’s right, title and interest in and to specified patent rights and other specified assets solely related to ENPP1. The Company issued 8,294,360 shares of its Series A-2 Convertible Preferred Stock to Alexion in consideration for the sale and assignment to the Company of such assets, with an estimated fair value of $17.8 million. The Company will expense the assets acquired from Alexion as of the acquisition date because the Company will use them in research and development activities and believes they have no alternative future uses.

(b) Increase in Authorized Series A-2 Convertible Preferred Stock

On July 17, 2020, the Company increased the number of authorized shares of Series A-2 Convertible Preferred Stock from 47,132,862 to 55,427,222.

On July 17, 2020, the Company increased the number of authorized shares of common stock from 129,000,000 to 138,000,000.

(d) 2020 Stock Incentive Plan

On July 17, 2020, the Company’s stockholders approved the 2020 Stock Incentive Plan (the “2020 Plan”), which became effective on July 23, 2020. The 2020 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. The number of shares of the Company’s common stock reserved for issuance under the 2020 Plan is 1,588,315 shares; plus the shares of common stock remaining available for issuance under the 2017 Plan as of July 23, 2020. The number of shares reserved shall be annually increased on January 1, 2021 and each January 1 thereafter through January 1, 2030 by the lower of (i) 4% of the number of shares of common stock outstanding on the first day of such fiscal year and (ii) an amount determined by the Company’s board of directors.

The shares of the Company’s common stock subject to outstanding awards under the 2017 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right will be added back to the shares of common stock available for issuance under the 2020 Plan. No more than 1,588,315 shares of the Company’s common stock may be granted subject to incentive stock options under the 2020 Plan.

(e) 2020 Employee Stock Purchase Plan

On July 17, 2020, the Company’s stockholders approved the 2020 Employee Stock Purchase Plan (the “ESPP”), which became effective on July 23, 2020. The ESPP initially provides participating employees with the opportunity to purchase up to an aggregate of 198,539 shares of the Company’s common stock. The number of shares of common stock reserved for issuance under the ESPP will automatically increase on January 1, 2021 and each January 1 thereafter through January 1, 2031, in an amount equal to the lowest of (1) 397,079 shares of the Company’s common stock, (2) 1% of the number of shares of the Company’s common stock outstanding on the first day of such fiscal year and (3) an amount determined by the Company’s board of directors.

(f) Automatic Conversion Waiver and Reverse Stock Split

On July 17, 2020, the Company eliminated the per share and gross proceeds thresholds for a firm-commitment underwritten public offering that triggers the automatic conversion of all outstanding shares of preferred stock into common stock. In addition, on July 17, 2020, the Company effected a one-for-7.4730 reverse stock split of the Company’s common stock. All share and per share amounts in the consolidated financial statements and notes thereto have been retroactively adjusted for all periods presented to give effect to this reverse stock split, including reclassifying an amount equal to the reduction in par value of common stock to additional paid-in capital. Shares of common stock underlying outstanding stock options and other equity instruments were proportionately reduced and the respective exercise prices, if applicable, were proportionately increased in accordance with the terms of the appropriate securities agreements. Shares of common stock reserved for issuance upon the conversion of the Company’s convertible preferred stock were proportionately reduced and the respective conversion prices were proportionately increased. Stockholders entitled to fractional shares as a result of the reverse stock split will receive a cash payment in lieu of receiving fractional shares.

(g) Initial Public Offering

On July 28, 2020, the Company completed an IPO pursuant to which it issued 7,000,000 shares of its common stock at a public ofering price of $16.00 per share, and on July 30, 2020, the Company sold an additional 1,050,000 shares pursuant to the exercise by the underwriters of their option to purchase additional shares. The Company received net proceeds from its IPO, inclusive of the exercise by the underwriters of their option to purchase additional shares, of approximately $116.5 million, after deducting underwriting discounts and commissions and estimated offering expenses. Upon the closing of the IPO, all 104,277,222 shares of the then outstanding preferred stock automatically converted into 13,953,850 shares of common stock.

(h) Changes to Authorized Common Stock and Preferred Stock

On July 28, 2020, the Company amended and restated its certificate of incorporation to authorize 200,000,000 shares of common stock and 5,000,000 shares of preferred stock, which shares of preferred stock are currently undesignated.