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 income (Loss)	Accumulated deflicit
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 gain (loss) 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
Balances at Dec. 31, 2020	139,832	$ 5	415,824	11	(276,008)
Balances (in shares) at Dec. 31, 2020		47,959
Issuance of common stock in connection with employee stock purchase plan	224		224
Issuance of common stock in connection with employee stock purchase plan (in shares)		38
Issuance of common stock and pre-funded warrants in connection with public offering, net of offering costs (in shares)		1,000
Issuance of common stock in connection with exercise of stock options	146		146
Issuance of common stock in connection with exercise of stock options (in shares)		23
Stock-based compensation expense	1,757		1,757
Foreign currency translation adjustment	4			4
Unrealized gain (loss) on marketable securities	10			10
Net loss	(18,218)				(18,218)
Balances at Mar. 31, 2021	$ 123,755	$ 5	$ 417,951	$ 25	$ (294,226)
Balances (in shares) at Mar. 31, 2021		49,020