Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock Public offering	Common Stock Private Placement	Common Stock At-the-market sales	Common Stock	Additional Paid-in Capital Public offering	Additional Paid-in Capital Private Placement	Additional Paid-in Capital At-the-market sales	Additional Paid-in Capital	Accumulated Deficit	Public offering	Private Placement	At-the-market sales	Total
Balance at Dec. 31, 2016				$ 3				$ 235,754	$ (193,468)				$ 42,289
Balance (in shares) at Dec. 31, 2016				28,759,731
Increase (decrease) in stockholders' equity
Share-based compensation - stock options and RSUs								3,651					3,651
Issuance of common stock					$ 18,535					$ 18,535
Issuance of common stock (in shares)	5,333,334
Vesting of RSUs (in shares)				16,667
Issuance of common stock upon exercise of options								152					152
Issuance of common stock upon exercise of options (in shares)				76,610
Net loss									(28,304)				(28,304)
Balance at Dec. 31, 2017				$ 3				258,092	(221,772)				36,323
Balance (in shares) at Dec. 31, 2017				34,186,342
Increase (decrease) in stockholders' equity
Share-based compensation - stock options and RSUs								3,630					3,630
Vesting of RSUs (in shares)				190,987
Net loss									(19,779)				(19,779)
Balance at Dec. 31, 2018				$ 3				261,722	(241,551)				20,174
Balance (in shares) at Dec. 31, 2018				34,377,329
Increase (decrease) in stockholders' equity
Adjustment to derivative liabilities upon adoption of ASU 2017-11								213	(213)
Share-based compensation - stock options and RSUs								1,762					1,762
Issuance of common stock	$ 2	$ 1	$ 1		$ 12,685	$ 7,809	$ 21,753			$ 12,687	$ 7,810	$ 21,754
Issuance of common stock (in shares)	14,526,315	8,426,750	12,242,436
Vesting of RSUs (in shares)				145,204
Issuance of common stock upon exercise of options								164					164
Issuance of common stock upon exercise of options (in shares)				92,271
Net loss				$ 0				0	(18,606)				(18,606)
Balance at Dec. 31, 2019				$ 7				$ 306,108	$ (260,370)				$ 45,745
Balance (in shares) at Dec. 31, 2019				69,810,305