Stockholders' Equity - Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands							1 Months Ended	2 Months Ended	9 Months Ended	12 Months Ended
	Dec. 11, 2020	Jul. 13, 2020	Apr. 07, 2020	Dec. 23, 2019	Mar. 04, 2019	May 05, 1998	Nov. 30, 2018	Feb. 28, 2021	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Stock
Par value (per share)									$ 0.001	$ 0.001	$ 0.001
Shares authorized (in shares)									140,000,000	140,000,000	140,000,000
Proceeds from issuance				$ 3,900							$ 10,072
Warrant exercise price (per share)									$ 1.28	$ 1.28	$ 0.75
Net proceeds from offering of common stock								$ 16,300
Common stock, shares reserved for future issuance									35,750,149	35,750,149
Board of Director
Class of Stock
Ownership percentage									12.00%	12.00%
"At-The-Market" Equity Program
Class of Stock
Maximum value of shares that are permitted to be sold, subject to certain limitations										$ 35,400
Stock issued (in shares)										3,608,713	532,700
Net proceeds from offering of common stock												$ 0
Percentage of fixed commission expense of gross proceeds of shares sold in ATM agreement							3.00%
Net proceeds from offering of common stock										$ 12,300	$ 1,600
Lincoln Park Capital Fund, LLC ("Investor")
Class of Stock
Value of shares investor has committed to purchase					$ 35,000
Maximum value of shares that are permitted to be sold, subject to certain limitations										$ 29,500
Stock issued (in shares)					269,749					750,000	1,535,848
Stock issued (per share)					$ 2.84
Net proceeds from offering of common stock										$ 1,700	$ 3,700
Common Stock
Class of Stock
Stock issued (in shares)						149,960
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 | "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	0.5		3,039,514
Proceeds from issuance	$ 5,000		$ 5,000
Warrant exercise price (per share)			$ 2.28
Combined purchase price (per share)			1.645
Stock price underlying warrants (per share)			$ 0.125
April 2020 Private Placement | Common Stock Warrants
Class of Stock
Stock issued (in shares)	69,941
Warrant exercise price (per share)	$ 1.82
April 2020 Private Placement | Pre-funded Warrants
Class of Stock
Stock issued (in shares)	2,677,311
Warrant exercise price (per share)	$ 0.01								$ 0.5	$ 0.5
April 2020 Private Placement | Warrants
Class of Stock
Stock issued (in shares)	1,373,626
Warrant exercise price (per share)	$ 2.71								$ 1.81	$ 1.81
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
Class of Stock
Stock issued (in shares)		749,993
Proceeds from issuance		$ 5,100
Combined purchase price (per share)		$ 1.845
Stock price underlying warrants (per share)		$ 0.125
July 2020 Private Placement | Pre-funded Warrants
Class of Stock
Shares of common stock that may be purchased upon exercise of warrants		2,014,234
Warrant exercise price (per share)		$ 0.01
July 2020 Private Placement | Warrants
Class of Stock
Shares of common stock that may be purchased upon exercise of warrants		2,764,227
Warrant exercise price (per share)		$ 2.58
July 2020 Private Placement Second Closing
Class of Stock
Stock issued (in shares)		784,615
Shares of common stock that may be purchased upon exercise of warrants		274,615
Warrant exercise price (per share)		$ 9.75
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any		$ 5,100
Stock price (in dollars per share)		$ 0.01
Combined purchase price (per share)		$ 6.50
July 2020 Private Placement Second Closing | Common Stock Warrants
Class of Stock
Number of common warrants		0.35
Stock price (in dollars per share)		$ 0.04375
July 2020 Private Placement Second Closing | Pre-funded Warrants
Class of Stock
Warrant exercise price (per share)		$ 6.45625
July 2020 Private Placement and July 2020 Private Placement Second Closing in Aggregate
Class of Stock
Net proceeds from offering of common stock										$ 5,000