Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Convertible preferred stock (as converted)	Total
Balances at beginning at Dec. 31, 2018					$ 209,668
Balances at beginning (in shares) at Dec. 31, 2018					17,248,259
Balances at beginning at Dec. 31, 2018	$ 1	$ 3,593	$ (4)	$ (96,622)		$ (93,032)
Balances at beginning (in shares) at Dec. 31, 2018	2,119,872
Issuance of common stock upon exercise of options		13				13
Issuance of common stock upon exercise of options (in shares)	3,385
Stock-based compensation		776				776
Unrealized gain on fair value of investments			28			28
Unrealized currency exchange loss			(1)			(1)
Net loss				(13,579)		(13,579)
Balances at end at Mar. 31, 2019					$ 209,668
Balances at end (in shares) at Mar. 31, 2019					17,248,259
Balances at end at Mar. 31, 2019	$ 1	4,382	23	(110,201)		(105,795)
Balances at end (in shares) at Mar. 31, 2019	2,123,257
Balances at beginning at Dec. 31, 2019	$ 3	351,039	16	(164,106)		186,952
Balances at beginning (in shares) at Dec. 31, 2019	27,970,167
Issuance of common stock upon exercise of options		419				419
Issuance of common stock upon exercise of options (in shares)	86,872
Vesting of early exercised stock options		4				4
Issuance of common stock under the Employee Stock Purchase Plan		533				533
Issuance of common stock under the Employee Stock Purchase Plan (shares)	36,556
Stock-based compensation		2,482				2,482
Unrealized gain on fair value of investments			163			163
Net loss				(20,418)		(20,418)
Balances at end at Mar. 31, 2020	$ 3	$ 354,477	$ 179	$ (184,524)		$ 170,135
Balances at end (in shares) at Mar. 31, 2020	28,093,595