Consolidated Statements of Shareholders' Equity Statement - USD ($) $ in Thousands	Total	Common Stock	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning Balance (in shares) at Dec. 31, 2019		38,434,488
Beginning Balance at Dec. 31, 2019	$ 47,529	$ 436,122	$ 12	$ (388,605)
Stock issued under employee equity incentive plans (in shares)		815,375
Stock issued under employee equity incentive plans	325	$ 325
Stock-based compensation expense	1,822	$ 1,822
Unrealized gain (loss) on available for sale securities	(6)		(6)
Net income (loss)	(5,399)			(5,399)
Ending Balance (in shares) at Mar. 31, 2020		39,249,863
Ending Balance at Mar. 31, 2020	44,271	$ 438,269	6	(394,004)
Beginning Balance (in shares) at Dec. 31, 2019		38,434,488
Beginning Balance at Dec. 31, 2019	47,529	$ 436,122	12	(388,605)
Net income (loss)	(11,951)
Ending Balance (in shares) at Jun. 30, 2020		40,220,491
Ending Balance at Jun. 30, 2020	42,455	$ 442,998	13	(400,556)
Beginning Balance (in shares) at Mar. 31, 2020		39,249,863
Beginning Balance at Mar. 31, 2020	44,271	$ 438,269	6	(394,004)
At the market equity offering (in shares)		803,528
At the market equity offering	2,474	$ 2,474
Stock issued under employee equity incentive plans (in shares)		167,100
Stock issued under employee equity incentive plans	12	$ 12
Stock-based compensation expense	2,243	$ 2,243
Unrealized gain (loss) on available for sale securities	7		7
Net income (loss)	(6,552)			(6,552)
Ending Balance (in shares) at Jun. 30, 2020		40,220,491
Ending Balance at Jun. 30, 2020	42,455	$ 442,998	13	(400,556)
Beginning Balance (in shares) at Dec. 31, 2020		51,078,942
Beginning Balance at Dec. 31, 2020	52,870	$ 467,957	47	(415,134)
Stock issued under employee equity incentive plans (in shares)		1,133,479
Stock issued under employee equity incentive plans	1,063	$ 1,063
Stock-based compensation expense	1,432	$ 1,432
Net income (loss)	(8,075)			(8,075)
Ending Balance (in shares) at Mar. 31, 2021		52,212,421
Ending Balance at Mar. 31, 2021	47,290	$ 470,452	47	(423,209)
Beginning Balance (in shares) at Dec. 31, 2020		51,078,942
Beginning Balance at Dec. 31, 2020	52,870	$ 467,957	47	(415,134)
Net income (loss)	(12,457)
Ending Balance (in shares) at Jun. 30, 2021		52,352,564
Ending Balance at Jun. 30, 2021	44,414	$ 471,958	47	(427,591)
Beginning Balance (in shares) at Mar. 31, 2021		52,212,421
Beginning Balance at Mar. 31, 2021	47,290	$ 470,452	47	(423,209)
Stock issued under employee equity incentive plans (in shares)		140,143
Stock-based compensation expense	1,506	$ 1,506
Net income (loss)	(4,382)			(4,382)
Ending Balance (in shares) at Jun. 30, 2021		52,352,564
Ending Balance at Jun. 30, 2021	$ 44,414	$ 471,958	$ 47	$ (427,591)