Condensed Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Due To (From) Related Party	Convertible Preferred Stock	Non-voting Common Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Convertible preferred stock balance at Dec. 31, 2018			$ 60,917
Convertible preferred stock balance, shares at Dec. 31, 2018			9,501,620
Convertible preferred stock balance at Mar. 31, 2019			$ 60,917
Convertible preferred stock balance, shares at Mar. 31, 2019			9,501,620
Balance at Dec. 31, 2018	$ (65,828)	$ (2,511)			$ 4	$ 751		$ (64,072)
Balance, shares at Dec. 31, 2018					438,074
Exercise of stock options	10					10
Exercise of stock options, shares					7,566
Capital contribution from related party	23					23
Stock-based compensation expense	139					139
Net loss	(7,470)							(7,470)
Balance at Mar. 31, 2019	(73,126)	(2,511)			$ 4	923		(71,542)
Balance, shares at Mar. 31, 2019					445,640
Convertible preferred stock balance at Dec. 31, 2018			$ 60,917
Convertible preferred stock balance, shares at Dec. 31, 2018			9,501,620
Convertible preferred stock balance at Jun. 30, 2019			$ 122,785
Convertible preferred stock balance, shares at Jun. 30, 2019			14,192,617
Balance at Dec. 31, 2018	(65,828)	(2,511)			$ 4	751		(64,072)
Balance, shares at Dec. 31, 2018					438,074
Net loss	(18,146)
Balance at Jun. 30, 2019	(80,969)				$ 6	1,243		(82,218)
Balance, shares at Jun. 30, 2019					618,861
Convertible preferred stock balance at Mar. 31, 2019			$ 60,917
Convertible preferred stock balance, shares at Mar. 31, 2019			9,501,620
Issuance of Series C convertible preferred stock, net of issuance costs of $0.1 million			$ 61,868
Issuance of Series C convertible preferred stock, net of issuance costs of $0.1 million, shares			4,690,997
Convertible preferred stock balance at Jun. 30, 2019			$ 122,785
Convertible preferred stock balance, shares at Jun. 30, 2019			14,192,617
Balance at Mar. 31, 2019	(73,126)	(2,511)			$ 4	923		(71,542)
Balance, shares at Mar. 31, 2019					445,640
Exercise of stock options	154				$ 2	152
Exercise of stock options, shares					165,656
Issuance of common stock	11					11
Issuance of common stock, shares					7,565
Related party equity transaction	2,527	$ 2,511				16
Stock-based compensation expense	141					141
Net loss	(10,676)							(10,676)
Balance at Jun. 30, 2019	(80,969)				$ 6	1,243		(82,218)
Balance, shares at Jun. 30, 2019					618,861
Balance at Dec. 31, 2019	240,231			$ 64	$ 240	347,089	$ 43	(107,205)
Balance, shares at Dec. 31, 2019				6,431,205	24,053,921
Exercise of stock options	22				$ 1	21
Exercise of stock options, shares					15,885
Unrealized gain on investments	162						162
Stock-based compensation expense	1,220					1,220
Net loss	(17,624)							(17,624)
Balance at Mar. 31, 2020	224,011			$ 64	$ 241	348,330	205	(124,829)
Balance, shares at Mar. 31, 2020				6,431,205	24,069,806
Balance at Dec. 31, 2019	$ 240,231			$ 64	$ 240	347,089	43	(107,205)
Balance, shares at Dec. 31, 2019				6,431,205	24,053,921
Exercise of stock options, shares	94,303
Unrealized gain on investments	$ 253
Net loss	(36,463)
Balance at Jun. 30, 2020	206,953			$ 64	$ 242	350,019	296	(143,668)
Balance, shares at Jun. 30, 2020				6,431,205	24,162,876
Balance at Mar. 31, 2020	224,011			$ 64	$ 241	348,330	205	(124,829)
Balance, shares at Mar. 31, 2020				6,431,205	24,069,806
Exercise of stock options, net of shares withheld for taxes and exercise costs	(551)				$ 1	(552)
Exercise of stock options, net of shares withheld for taxes and exercise costs, shares					67,947
Issuance of common stock upon restricted stock unit settlement, shares					1,828
Purchases under employee stock purchase plan	317					317
Purchases under employee stock purchase plan, shares					23,295
Unrealized gain on investments	91						91
Stock-based compensation expense	1,924					1,924
Net loss	(18,839)							(18,839)
Balance at Jun. 30, 2020	$ 206,953			$ 64	$ 242	$ 350,019	$ 296	$ (143,668)
Balance, shares at Jun. 30, 2020				6,431,205	24,162,876