Statements of Stockholders' Equity - USD ($) $ in Thousands	At-the-Market Sales Agreement	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2018		$ 2	$ 158,912	$ (133,993)	$ 24,921
Balance (in shares) at Dec. 31, 2018		17,095,456
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under stock incentive plans			13		13
Issuance of common stock under stock incentive plans (in shares)		12,607
Stock-based compensation expense			704		704
Net loss				(4,256)	(4,256)
Balance at Mar. 31, 2019		$ 2	159,629	(138,249)	21,382
Balance (in shares) at Mar. 31, 2019		17,108,063
Balance at Dec. 31, 2018		$ 2	158,912	(133,993)	24,921
Balance (in shares) at Dec. 31, 2018		17,095,456
Increase (Decrease) in Stockholders' Equity
Net loss					(7,926)
Balance at Jun. 30, 2019		$ 2	160,564	(141,919)	18,647
Balance (in shares) at Jun. 30, 2019		17,151,290
Balance at Mar. 31, 2019		$ 2	159,629	(138,249)	21,382
Balance (in shares) at Mar. 31, 2019		17,108,063
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under stock incentive plans			137		137
Issuance of common stock under stock incentive plans (in shares)		43,227
Stock-based compensation expense			798		798
Net loss				(3,670)	(3,670)
Balance at Jun. 30, 2019		$ 2	160,564	(141,919)	18,647
Balance (in shares) at Jun. 30, 2019		17,151,290
Balance at Dec. 31, 2019		$ 2	167,149	(148,662)	18,489
Balance (in shares) at Dec. 31, 2019		18,081,753
Increase (Decrease) in Stockholders' Equity
Issuance of common stock in at-the-market offering, net of issuance costs			2,084		2,084
Issuance of common stock (in shares)		468,427
Issuance of common stock under stock incentive plans			315		315
Issuance of common stock under stock incentive plans (in shares)		88,375
Stock-based compensation expense			805		805
Net loss				(1,732)	(1,732)
Balance at Mar. 31, 2020		$ 2	170,353	(150,394)	19,961
Balance (in shares) at Mar. 31, 2020		18,638,555
Balance at Dec. 31, 2019		$ 2	167,149	(148,662)	18,489
Balance (in shares) at Dec. 31, 2019		18,081,753
Increase (Decrease) in Stockholders' Equity
Issuance of common stock (in shares)	468,427
Net loss					(3,026)
Balance at Jun. 30, 2020		$ 2	172,098	(151,688)	20,412
Balance (in shares) at Jun. 30, 2020		18,869,775
Balance at Mar. 31, 2020		$ 2	170,353	(150,394)	19,961
Balance (in shares) at Mar. 31, 2020		18,638,555
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under stock incentive plans			827		827
Issuance of common stock under stock incentive plans (in shares)		231,220
Stock-based compensation expense			918		918
Net loss				(1,294)	(1,294)
Balance at Jun. 30, 2020		$ 2	$ 172,098	$ (151,688)	$ 20,412
Balance (in shares) at Jun. 30, 2020		18,869,775