Condensed Consolidated Statements of Stockholders' Deficit - USD ($) $ in Thousands	Total	Convertible Note Mann Group	Convertible Note Interest Mann Group	2024 Convertible Notes	2024 Convertible Note Interest	At-the-market Placement	Common Stock	Common Stock Convertible Note Mann Group	Common Stock Convertible Note Interest Mann Group	Common Stock 2024 Convertible Notes	Common Stock 2024 Convertible Note Interest	Common Stock At-the-market Placement	Additional Paid-in Capital	Additional Paid-in Capital Convertible Note Mann Group	Additional Paid-in Capital Convertible Note Interest Mann Group	Additional Paid-in Capital 2024 Convertible Notes	Additional Paid-in Capital 2024 Convertible Note Interest	Additional Paid-in Capital At-the-market Placement	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2020	$ (180,419)						$ 2,421						$ 2,866,303							$ (3,049,143)
Beginning Balance (in shares) at Dec. 31, 2020							242,118,000
Net issuance of common stock associated with stock options and restricted stock units	397						$ 4						393
Net issuance of common stock associated with stock options and restricted stock units (in shares)							390,000
Issuance of common stock under Employee Stock Purchase Plan	390						$ 3						387
Issuance of common stock under Employee Stock Purchase Plan (in shares)							292,981
Stock-based compensation expense	1,935												1,935
Issuance of common stock pursuant to conversion notes		$ 9,573	$ 427	$ 5,000				$ 38	$ 2	$ 17				$ 9,535	$ 425	$ 4,983
Issuance of common stock pursuant to conversion notes (in shares)								3,830,000	170,000	1,667,000
Issuance of common stock pursuant to payoff of the 2024 convertible note interest					$ 143												$ 143
Issuance of common stock pursuant to payoff of the 2024 convertible note interest (in shares)											27,000
Issuance of at-the-market placement						$ 1,886						$ 6						$ 1,880
Issuance of at-the-market placement (in shares)												578,000
Issuance costs associated with at-the- market placement	(38)												(38)
Net loss	(12,916)																			(12,916)
Ending Balance at Mar. 31, 2021	(173,622)						$ 2,491						2,885,946							(3,062,059)
Ending Balance (in shares) at Mar. 31, 2021							249,073,000
Beginning Balance at Dec. 31, 2021	(209,349)						$ 2,515						2,918,205							(3,130,069)
Beginning Balance (in shares) at Dec. 31, 2021							251,478,000
Net issuance of common stock associated with stock options and restricted stock units	129						$ 4						125
Net issuance of common stock associated with stock options and restricted stock units (in shares)							450,000
Issuance of common stock under Employee Stock Purchase Plan	740						$ 2						738
Issuance of common stock under Employee Stock Purchase Plan (in shares)							233,401
Stock-based compensation expense	2,806												2,806
Issuance of common stock from market price stock purchase plan	684						$ 3						681
Issuance of common stock from Market Price Stock Purchase Plan (in shares)							252,000
Cumulative loss on available-for-sale securities	(1,076)																		$ (1,076)
Net loss	(25,998)																			(25,998)
Ending Balance at Mar. 31, 2022	$ (232,064)						$ 2,524						$ 2,922,555						$ (1,076)	$ (3,156,067)
Ending Balance (in shares) at Mar. 31, 2022							252,413,000