Stockholders' Equity (Deficit) - Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands							1 Months Ended	12 Months Ended			21 Months Ended
	Mar. 31, 2022	Jul. 13, 2020	Apr. 07, 2020	Dec. 23, 2019	Mar. 04, 2019	May 05, 1998	Nov. 30, 2018	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2021	Mar. 04, 2022
Class of Stock
Common stock, shares reserved for future issuance								23,918,172			23,918,172	14,906,278
Par value (per share)								$ 0.001	$ 0.001		$ 0.001
Proceeds from issuance				$ 3,900						$ 10,072
Warrant exercised price (per share)								$ 2.04	$ 1.28		$ 2.04
Directors [Member]
Class of Stock
Ownership percentage								4.00%			4.00%
"At-The-Market" Equity Program
Class of Stock
Maximum value of shares that are permitted to be sold, subject to certain limitations	$ 19,500
Stock issued (in shares)								5,117,357	3,608,713
Percentage of fixed commission expense of gross proceeds of shares sold in ATM agreement							3.00%
Net proceeds from offering of common stock								$ 15,300	$ 12,300
Lincoln Park Capital Fund, LLC ("Investor")
Class of Stock
Value of shares which may be sold					$ 35,000
Duration over which common stock purchase agreement may be sold					36 months
Stock issued (in shares)					269,749			800,000	750,000
Stock issued (per share)					$ 2.84
Net proceeds from offering of common stock								$ 4,200	$ 1,700
Common Stock [Member]
Class of Stock
Stock issued (in shares)						149,960		5,918,000	8,218,000	2,068,000
Sale price of common shares subject to the liquidation put						$ 128.00
Minimum closing sales price of common stock to issue termination notice to put holders								$ 256.00
Price exceeds on number of days								20 days
Liquidation put shares no longer held by original holders								49,993
Shares held by put holders								4,472
Put Rights outstanding								0
Remaining shares of common stock subject to the liquidation put								95,494
Common Stock [Member] | "At-The-Market" Equity Program
Class of Stock
Net proceeds from offering of common stock							$ 50,000
April 2020 Private Placement
Class of Stock
Stock issued (in shares)			3,039,514
Shares of common stock that may be purchased upon exercise of warrants			3,039,514
Warrant exercised price (per share)			$ 2.28
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any			$ 5,000
Combined purchase price (per share)			$ 1.645
Stock price underlying warrants (per share)			$ 0.125
April 2020 Private Placement Second Closing
Class of Stock
Stock issued (in shares)			2,747,252
Ownership percentage			19.99%
Shares of common stock that may be purchased upon exercise of warrants			1,373,626
Warrant exercised price (per share)			$ 2.71
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any			$ 5,000
Stock price (in dollars per share)			$ 0.01
April 2020 Private Placement and April 2020 Private Placement Second Closing in Aggregate
Class of Stock
Net proceeds from offering of common stock											$ 9,800
July 2020 Private Placement Second Closing
Class of Stock
Proceeds from issuance		$ 5,100
July 2020 Private Placement Second Closing | Pre-funded Warrants
Class of Stock
Shares of common stock that may be purchased upon exercise of warrants		784,615
Stock price (in dollars per share)		$ 0.01
July 2020 Private Placement Second Closing | Warrants
Class of Stock
Shares of common stock that may be purchased upon exercise of warrants		274,615
Stock price (in dollars per share)		$ 9.75