Stockholders' Equity - Common Stock (Details) - USD ($) $ / shares in Units, $ in Millions				1 Months Ended	3 Months Ended
	Jul. 13, 2020	Dec. 23, 2019	Mar. 04, 2019	Nov. 30, 2018	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Class of Stock
Par value (per share)					$ 0.001		$ 0.001
Proceeds from issuance		$ 3.9
"At-The-Market" Equity Program
Class of Stock
Maximum value of shares that are permitted to be sold, subject to certain limitations					$ 19.5
Stock issued (in shares)					0	2,394,956
Net proceeds from offering of common stock						$ 12.1
Percentage of fixed commission expense of gross proceeds of shares sold in ATM agreement				3.00%
Lincoln Park Capital Fund, LLC ("Investor")
Class of Stock
Value of shares which may be sold			$ 35.0
Duration over which common stock purchase agreement may be sold			36 months
Stock issued (in shares)			269,749			800,000
Stock issued (per share)			$ 2.84
Net proceeds from offering of common stock						$ 4.2
Common Stock [Member]
Class of Stock
Stock issued (in shares)						3,195,000
Common Stock [Member] | "At-The-Market" Equity Program
Class of Stock
Net proceeds from offering of common stock				$ 50.0
July 2020 Private Placement Second Closing
Class of Stock
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any	$ 5.1
July 2020 Private Placement Second Closing | Pre-funded Warrants
Class of Stock
Stock issued (in shares)	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
Warrant exercised price (per share)	$ 9.75