Consolidated Statements of Changes in Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Series A Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Balance at the beginning of the period at Dec. 31, 2016	$ 58,897		$ (24,945)	$ (20,177)	$ (45,122)
Balance at the beginning of the period (in shares) at Dec. 31, 2016	28,730,005	166,373
Changes in equity
Receipt of stock subscription proceeds for stock issued as of the prior year end			(4,496)		(4,496)
Issuance of stock			3,207		3,207
Issuance of stock (in shares)	6,516,142
Temporary Equity, Stock Issued During Period, Value, New Issues Upon Maturity of Convertible Notes	$ 13,358
Stock dividends issued (in shares)	950,046
Series A convertible preferred stock dividends issued	$ (1,947)		(846)	2,793	1,947
Series A convertible preferred stock dividend			352		352
Stock-based compensation			1,608		1,608
Net Loss				(24,656)	(24,656)
Balance at the end of the period at Dec. 31, 2017	$ 74,202		(15,140)	(47,626)	(62,766)
Balance at the end of the period (shares) at Dec. 31, 2017	36,196,193	166,373
Changes in equity
Issuance of stock			25,079		25,079
Issuance of stock (in shares)		2,192,824
Stock dividends issued (in shares)	669,647
Series A convertible preferred stock dividend	$ 1,358		(1)	(1,357)	(1,358)
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
Issuance of common stock upon exercise (in shares)		974
Reclassification of warrant liability to equity upon initial public offering			10,236		10,236
Exercise of stock options			10		10
Stock-based compensation			1,658		1,658
Net Loss				(22,105)	(22,105)
Balance at the end of the period at Dec. 31, 2018		$ 1	$ 97,401	$ (71,088)	$ 26,314
Balance at the end of the period (shares) at Dec. 31, 2018		8,104,757