STATEMENTS OF STOCKHOLDERS' (DEFICIT) EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional paid-in capital	Convertible Preferred Stock	Accumulated Other Comprehensive Loss	Accumulated Deficit	IPO	IPO Common Stock	IPO Additional paid-in capital	Follow-On Public Offering	Follow-On Public Offering Common Stock	Follow-On Public Offering Additional paid-in capital
Balance at Dec. 31, 2015	$ (1,142)	$ 1	$ 6,390	$ 81,513	$ 0	$ (89,046)
Common stock, outstanding (in shares) at Dec. 31, 2015		1,036,159
Preferred stock, outstanding (in shares) at Dec. 31, 2015				48,603,909
Stock options exercised	$ 189		189
Stock options exercised (in shares)	109,079	109,079
Shares issued during the period	$ 12,348			$ 12,348
Shares issued during the period (in shares)				9,124,084
Exercise of Series C preferred stock warrants	277			$ 277
Exercise of Series C preferred stock warrants (in shares)				258,880
Stock-based compensation expense	248		248
Net loss	(18,528)					(18,528)
Balance at Dec. 31, 2016	(6,608)	$ 1	6,827	$ 94,138	0	(107,574)
Common stock, outstanding (in shares) at Dec. 31, 2016		1,145,238
Preferred stock, outstanding (in shares) at Dec. 31, 2016				57,986,873
Stock options exercised	$ 235		235
Stock options exercised (in shares)	127,122	127,122
Shares issued during the period	$ 24,968			$ 24,968
Shares issued during the period (in shares)				18,248,177
Stock-based compensation expense	243		243
Net loss	(17,511)					(17,511)
Balance at Dec. 31, 2017	$ 1,327	$ 1	7,305	$ 119,106	0	(125,085)
Common stock, outstanding (in shares) at Dec. 31, 2017	1,272,360	1,272,360
Preferred stock, outstanding (in shares) at Dec. 31, 2017	76,235,050			76,235,050
Stock options exercised (in shares)	301,058
Stock options and warrants exercised	$ 558		558
Stock options and warrants exercised (in shares)		377,820
Shares issued during the period	95		95				$ 112,040	$ 8	$ 112,032	$ 69,785	$ 2	$ 69,783
Shares issued during the period (in shares)		2,285						7,762,500			1,875,000
Conversion of preferred stock to common stock	0	$ 12	119,094	$ (119,106)
Conversion of preferred stock to common stock (in shares)		12,111,710		(76,235,050)
Conversion of warrants to purchase preferred stock to warrants to purchase common stock	855		855
Stock-based compensation expense	1,219		1,219
Comprehensive loss	(52)				(52)
Net loss	(21,828)					(21,828)
Balance at Dec. 31, 2018	$ 163,999	$ 23	$ 310,941	$ 0	$ (52)	$ (146,913)
Common stock, outstanding (in shares) at Dec. 31, 2018	23,401,675	23,401,675
Preferred stock, outstanding (in shares) at Dec. 31, 2018	0			0