Consolidated Statements of Changes in Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Series A Convertible Preferred Stock	Common Stock Private placement	Common Stock IPO	Common Stock	Additional Paid-In Capital Private placement	Additional Paid-In Capital IPO	Additional Paid-In Capital	Accumulated Deficit	Private placement	IPO	Total
Balances at the beginning of the period at Dec. 31, 2017	$ 74,202						$ (15,140)	$ (47,626)			$ (62,766)
Balances at the beginning of the period (in shares) at Dec. 31, 2017	36,196,193			166,373
Changes in equity
Series A convertible preferred stock dividends ($0.04 per share)	$ 1,358						(1)	(1,357)			(1,358)
Series A convertible preferred stock dividends (in shares)	669,647
Conversion of Series A convertible preferred stock into common stock upon initial public offering	$ (75,560)			$ 1			75,559				75,560
Conversion of Series A convertible preferred stock into common stock upon initial public offering (in shares)	(36,865,840)			5,744,586
Reclassification of warrant liability to equity upon initial public offering							10,236				10,236
Issuance of common stock						$ 25,079				$ 25,079
Issuance of common stock (in shares)			2,192,824
Exercise of stock options							10				10
Exercise of stock options (in shares)				974,000
Stock-based compensation							1,658				1,658
Net loss								(22,105)			(22,105)
Balances at the end of the period at Dec. 31, 2018				$ 1			97,401	(71,088)			26,314
Balances at the end of the period (shares) at Dec. 31, 2018				8,104,757
Changes in equity
Issuance of common stock					$ 4,958				$ 4,958
Issuance of common stock (in shares)		801,820
Exercise of stock options							35				35
Exercise of stock options (in shares)				11,884
Stock-based compensation							2,010				2,010
Net loss								(29,681)			(29,681)
Balances at the end of the period at Dec. 31, 2019				$ 1			$ 104,404	$ (100,769)			$ 3,636
Balances at the end of the period (shares) at Dec. 31, 2019				8,918,461