Subsequent Events - Additional Information (Details) $ / shares in Units, $ in Millions					1 Months Ended	6 Months Ended
	Jul. 30, 2020 USD ($) shares	Jul. 28, 2020 $ / shares shares	Jul. 23, 2020 shares	Jul. 17, 2020 shares	Jul. 31, 2020 USD ($) shares	Jun. 30, 2020 shares	Jul. 16, 2020 shares	Mar. 31, 2020 shares	Dec. 31, 2019 shares	Jun. 30, 2019 shares	Mar. 31, 2019 shares	Dec. 31, 2018 shares
Subsequent Event [Line Items]
Number of authorized shares of common stock						129,000,000			129,000,000
Share based compensation options to purchase number of common stock						2,083,218			1,635,427			822,557
Convertible preferred stock, shares outstanding						95,982,862			72,416,431
Number of common stock issued upon conversion						12,843,940			9,690,393
Common Stock
Subsequent Event [Line Items]
Reverse stock split, description						one-for-7.4730
2020 Stock Incentive Plan
Subsequent Event [Line Items]
Plan description						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.
2020 Employee Stock Purchase Plan
Subsequent Event [Line Items]
Plan description						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.
Series A-2 Convertible Preferred Stock
Subsequent Event [Line Items]
Convertible preferred stock, shares outstanding						47,132,862		23,566,431	23,566,431	23,566,431	23,566,431	7,482,515
Number of common stock issued upon conversion						6,307,084			3,153,537
Subsequent Event
Subsequent Event [Line Items]
Number of preferred stock authorized		5,000,000
Number of authorized shares of common stock		200,000,000		138,000,000			129,000,000
Reverse stock split				0.1338
Proceeds from issuance of shares | $	$ 116.5
Convertible preferred stock, shares outstanding		104,277,222
Number of common stock issued upon conversion		13,953,850
Subsequent Event | IPO
Subsequent Event [Line Items]
Shares issued		7,000,000
Shares issued, price per share | $ / shares		$ 16.00
Subsequent Event | Underwriters
Subsequent Event [Line Items]
Shares issued	1,050,000
Subsequent Event | Common Stock
Subsequent Event [Line Items]
Reverse stock split				0.1338
Subsequent Event | 2020 Stock Incentive Plan
Subsequent Event [Line Items]
Common stock reserved for issuance			1,588,315
Number of common stock reserved for issuance increase percentage on stock outstanding			4.00%
Subsequent Event | 2020 Stock Incentive Plan | Maximum
Subsequent Event [Line Items]
Maximum common stock granted, under 2020 plan			1,588,315
Subsequent Event | 2020 Employee Stock Purchase Plan
Subsequent Event [Line Items]
Number of common stock reserved for issuance increase percentage on stock outstanding			1.00%
Share based compensation options to purchase number of common stock			198,539
Increase in additional number of shares to be issued			397,079
Subsequent Event | Series A-2 Convertible Preferred Stock
Subsequent Event [Line Items]
Number of preferred stock authorized				55,427,222			47,132,862
Alexion Pharmaceuticals, Inc | Subsequent Event | Intellectual Property
Subsequent Event [Line Items]
Acquisition of intellectual property, estimated fair value | $					$ 17.8
Alexion Pharmaceuticals, Inc | Subsequent Event | Series A-2 Convertible Preferred Stock
Subsequent Event [Line Items]
Preferred stock, issued					8,294,360