Statements of Stockholders' Equity - USD ($) $ in Thousands	At-the-Market Sales Agreement Common Stock	At-the-Market Sales Agreement Additional Paid-In Capital	At-the-Market Sales Agreement	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2017				$ 1	$ 128,422	$ (117,539)	$ 10,884
Balance (in shares) at Dec. 31, 2017				12,817,201
Increase (Decrease) in Stockholders' Equity
Adjustment to opening balance for adoption of new accounting standard						1,300	1,300
Issuance of common stock, net of issuance costs				$ 1	24,523		24,524
Issuance of common stock (in shares)				3,772,447
Issuance of common stock under stock incentive plans					2,503		2,503
Issuance of common stock under stock incentive plans (in shares)				505,808
Issuance of warrant					43		43
Compensation expense related to vesting of common stock issued to GLOBALFOUNDRIES					753		753
Stock-based compensation expense					2,668		2,668
Net loss						(17,754)	(17,754)
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, net of issuance costs		$ 4,734	$ 4,734
Issuance of common stock (in shares)	888,987
Issuance of common stock under stock incentive plans					282		282
Issuance of common stock under stock incentive plans (in shares)				97,310
Modification of warrant in conjunction with 2019 Credit Facility					(19)		(19)
Stock-based compensation expense					3,240		3,240
Net loss						(14,669)	(14,669)
Balance at Dec. 31, 2019				$ 2	$ 167,149	$ (148,662)	$ 18,489
Balance (in shares) at Dec. 31, 2019				18,081,753