Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive (Loss) Income	Accumulated Deficit
Balances at Dec. 31, 2018	$ 67,428	$ 2	$ 184,314	$ (27)	$ (116,861)
Balances (in shares) at Dec. 31, 2018		24,140
Issuance of common stock in connection with employee stock purchase plan	143		143
Issuance of common stock in connection with employee stock purchase plan (in shares)		20
Issuance of common stock in connection with exercise of stock options	261		261
Issuance of common stock in connection with exercise of stock options (in shares)		52
Issuance of common stock and pre-funded warrants in connection with public offering, net of offering costs	64,503	$ 1	64,502
Issuance of common stock and pre-funded warrants in connection with public offering, net of offering costs (in shares)		4,625
Stock-based compensation expense	1,081		1,081
Unrealized (loss) gain on marketable securities	40			40
Net loss	(17,167)				(17,167)
Balances at Mar. 31, 2019	116,289	$ 3	250,301	13	(134,028)
Balances (in shares) at Mar. 31, 2019		28,837
Balances at Dec. 31, 2019	60,081	$ 3	255,142	51	(195,115)
Balances (in shares) at Dec. 31, 2019		29,084
Issuance of common stock in connection with employee stock purchase plan	174		174
Issuance of common stock in connection with employee stock purchase plan (in shares)		26
Issuance of common stock in connection with exercise of stock options	115		115
Issuance of common stock in connection with exercise of stock options (in shares)		37
Stock-based compensation expense	1,348		1,348
Unrealized (loss) gain on marketable securities	(185)			(185)
Net loss	(18,728)				(18,728)
Balances at Mar. 31, 2020	$ 42,805	$ 3	$ 256,779	$ (134)	$ (213,843)
Balances (in shares) at Mar. 31, 2020		29,147