Basis of Presentation and Summary of Significant Accounting Policies - Financial Instruments (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Nov. 25, 2019	Jun. 30, 2021	Jan. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Class of Stock [Line Items]
Amount paid for clearing fees		$ 19	$ 231
Offering costs paid on the issuance of common stock and warrants				$ 1	$ 0	$ 470	$ 474	$ 510
Proceeds from sale of common stock and warrants		$ 4,500	$ 2,300
Warrants issued (in shares)						310,860	539,152
Exercise price of common stock (USD per share)				$ 3.59		$ 3.59
Percentage of gross proceeds used to make payments on note			10.00%
Gross proceeds			$ 275
Payments on the Iliad Note				$ 0	450	$ 0	$ 976
Proceeds from issuance of warrants						$ 1,100
Warrants exercised (in shares)						156,446
Proceeds from the exercise of warrants				$ 0	$ 625	$ 527	$ 676
Iliad Note
Class of Stock [Line Items]
Percentage of gross proceeds used to make payments on note	10.00%
Payments on the Iliad Note			$ 226
Institutional investors
Class of Stock [Line Items]
Sale of common stock (in shares)		990,100	688,360
Sale of common stock (USD per share)		$ 5.05	$ 3.37
Warrants issued (in shares)			688,360			269,180	497,472
Exercise price of common stock (USD per share)			$ 3.37	$ 3.3700	$ 3.3700	$ 3.3700	$ 3.3700
Purchase price (USD per share)			$ 0.625
Placement agent
Class of Stock [Line Items]
Amount paid for placement agent commissions		$ 400	$ 193
Amount paid related to expenses for registered direct offering and concurrent private placement		$ 51	$ 50
Warrants issued (in shares)			48,185			41,680	41,680
Exercise price of common stock (USD per share)			$ 4.99	$ 4.9940	$ 4.9940	$ 4.9940	$ 4.9940