CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Restricted stock units	Restricted stock units Common Stock
Beginning balance (in shares) at Dec. 31, 2016		34,274,718
Beginning balance at Dec. 31, 2016	$ (63,492)	$ 3		$ 1,330	$ (64,825)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(31,007)				(31,007)
Accretion of dividends on convertible preferred stock	(357)				(357)
Conversion of convertible preferred stock to common stock (in shares)		18,163,158
Conversion of convertible preferred stock to common stock	48,207	$ 2	$ 48,205
Conversion of convertible preferred stock warrant to common stock warrant	1,191		1,191
Issuance of common stock from initial public offering, net of issuance costs (in shares)		7,187,500
Issuance of common stock from initial public offering, net of issuance costs	$ 77,789	$ 1	77,788
Exercise of common stock warrant (in shares)		79,363
Issuance of common stock to directors (in shares)		14,087
Vesting of restricted stock units (in shares)						4,930	4,930
Exercise of stock options (in shares)	876,121	876,121
Exercise of stock options	$ 1,108		1,108
Stock-based compensation expense	12,976		12,976
Other comprehensive income (loss)	(891)			(891)
Ending balance (in shares) at Dec. 31, 2017		60,599,877
Ending balance at Dec. 31, 2017	45,524	$ 6	141,268	439	(96,189)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(49,451)				(49,451)
Issuance of common stock from initial public offering, net of issuance costs (in shares)		1,675,000
Issuance of common stock from initial public offering, net of issuance costs	$ 57,829		57,829
Issuance of common stock to directors (in shares)		11,952
Vesting of restricted stock units (in shares)						143,390	143,390
Exercise of stock options (in shares)	1,486,218	1,486,218
Exercise of stock options	$ 3,133		3,133
Stock-based compensation expense	16,054		16,054
Other comprehensive income (loss)	103			103
Ending balance (in shares) at Dec. 31, 2018		63,916,437
Ending balance at Dec. 31, 2018	73,192	$ 6	218,284	542	(145,640)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(50,714)				(50,714)
Issuance of common stock from initial public offering, net of issuance costs (in shares)		1,825,000
Issuance of common stock from initial public offering, net of issuance costs	$ 101,303		101,303
Issuance of common stock to directors (in shares)		10,654
Vesting of restricted stock units (in shares)						521,460	521,460
Exercise of stock options (in shares)	1,194,471	1,194,471
Exercise of stock options	$ 4,899		4,899
Stock-based compensation expense	16,443		16,443
Other comprehensive income (loss)	(827)			(827)
Ending balance (in shares) at Dec. 31, 2019		67,468,022
Ending balance at Dec. 31, 2019	$ 205,237	$ 6	$ 340,929	$ (285)	$ (135,413)