Subsequent Events (Details) - USD ($) $ in Millions			2 Months Ended	12 Months Ended
	Feb. 28, 2021	Mar. 04, 2019	Feb. 28, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Subsequent Events
Net proceeds from offering of common stock			$ 16.3
"At-The-Market" Equity Program
Subsequent Events
Stock issued (in shares)				3,608,713	532,700
Net proceeds from offering of common stock						$ 0.0
Maximum value of shares that are permitted to be sold, subject to certain limitations				$ 35.4
Lincoln Park Capital Fund, LLC ("Investor")
Subsequent Events
Stock issued (in shares)		269,749		750,000	1,535,848
Net proceeds from offering of common stock				$ 1.7	$ 3.7
Maximum value of shares that are permitted to be sold, subject to certain limitations				$ 29.5
Subsequent Events | "At-The-Market" Equity Program
Subsequent Events
Stock issued (in shares)			2,394,956
Net proceeds from offering of common stock			$ 12.1
Maximum value of shares that are permitted to be sold, subject to certain limitations	$ 22.9
Subsequent Events | Lincoln Park Capital Fund, LLC ("Investor")
Subsequent Events
Stock issued (in shares)			800,000
Net proceeds from offering of common stock			$ 4.2
Maximum value of shares that are permitted to be sold, subject to certain limitations	$ 25.3