Statements of Changes in Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($)	Preferred Stock [Member] Series A-1 Convertible Preferred Stock	Preferred Stock [Member] Series A-2 Convertible Preferred Stock	Preferred Stock [Member] Series B Convertible Preferred Stock	Common stock	Additional paid‑in capital	Accumulated Deficit	Series A-1 Convertible Preferred Stock	Series A-2 Convertible Preferred Stock	Series B Convertible Preferred Stock	Total
Balance at Beginning of period at Dec. 31, 2018	$ 43,118,000
Balance at Beginning of period (in shares) at Dec. 31, 2018	44,418,606
Temporary equity
Sale of Series A‑1 convertible preferred stock, net of issuance costs	$ 19,981,000
Sale of Series A‑1 convertible preferred stock, net of issuance costs (in shares)	18,604,652
Balance at end of period at Mar. 31, 2019	$ 63,099,000
Balance at end of period (in shares) at Mar. 31, 2019	63,023,258
Balance at Beginning of period at Dec. 31, 2018				$ 4,195,649	$ 856,000	$ (13,029,000)				$ (12,173,000)
Stockholders' equity
Vesting of early exercise option awards					13,000					13,000
Vesting of early exercise option awards (in shares)				13,538
Share‑based compensation expense					231,000					231,000
Net loss						(7,669,000)				(7,669,000)
Balance at end of period at Mar. 31, 2019				$ 4,209,187	1,100,000	(20,698,000)				(19,598,000)
Balance at Beginning of period at Dec. 31, 2018	$ 43,118,000
Balance at Beginning of period (in shares) at Dec. 31, 2018	44,418,606
Balance at end of period at Dec. 31, 2019	$ 74,397,000	$ 46,311,000	$ 109,897,000				$ 74,397,000	$ 46,311,000	$ 109,897,000	230,605,000
Balance at end of period (in shares) at Dec. 31, 2019	63,023,258	22,209,301	33,592,907				63,023,258	22,209,301	33,592,907
Balance at Beginning of period at Dec. 31, 2018				4,195,649	856,000	(13,029,000)				(12,173,000)
Stockholders' equity
Net loss										(7,669,000)
Balance at end of period at Dec. 31, 2019				$ 4,293,039	2,410,000	(58,663,000)				(56,253,000)
Temporary equity
Conversion of convertible preferred stock upon initial public offering (in shares)	(63,023,258)	(22,209,301)	(33,592,907)
Stockholders' equity
Vesting of early exercise option awards					32,000					32,000
Vesting of early exercise option awards (in shares)				454,971
Sale of common stock upon consummation of initial public offering, net of issuance costs of $____				$ 1,000	227,498,000					227,499,000
Sale of common stock upon consummation of initial public offering, net of issuance costs of $____(in shares)				13,798,900
Conversion of convertible preferred stock upon initial public offering	$ (74,397,000)	$ (46,311,000)	$ (109,897,000)	$ 3,000	230,602,000					230,605,000
Conversion of convertible preferred stock upon initial public offering (in shares)				26,803,777
Share‑based compensation expense					2,368,000					2,368,000
Net loss						(17,585,000)				(17,585,000)
Balance at end of period at Mar. 31, 2020				$ 4,000	$ 462,910,000	$ (76,248,000)				$ 386,666,000
Balance at end of period (in shares) at Mar. 31, 2020				45,350,687