Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2015	$ 2	$ 194,468	$ (164,727)	$ 29,743
Balance (in shares) at Dec. 31, 2015	22,315,612
Increase (decrease) in stockholders' equity
Share-based compensation - stock options and RSUs		3,425		3,425
Vesting of RSUs (in shares)	16,666
Issuance of common stock in public offering, net of expenses	$ 1	37,527		37,528
Issuance of common stock in public offering, net of expenses (in shares)	6,338,583
Issuance of common stock upon exercise of options		334		334
Issuance of common stock upon exercise of options (in shares)	88,870
Net loss			(28,741)	(28,741)
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
Vesting of RSUs (in shares)	16,667
Issuance of common stock in public offering, net of expenses		18,535		18,535
Issuance of common stock in public offering, net of expenses (in shares)	5,333,334
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