Note 6 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Feb. 18, 2021
Subsidiary or Equity Method Investee [Line Items]
Share-Based Payment Arrangement, Expense	$ 1.2	$ 1.3
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 5.2
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	1 year 2 months 12 days
Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation (in shares)	96,659
Share-Based Payment Arrangement, Decrease for Tax Withholding Obligation	$ 0.5
Shares Withheld for Tax Withholding Obligation, Price Per Share (in dollars per share)	$ 4.98
At the market Offering [Member]
Subsidiary or Equity Method Investee [Line Items]
Equity Distribution Agreement, Maximum Number of Shares to be Sold (in shares)	2,173,274		60,000,000
Proceeds from Issuance or Sale of Equity	$ 11.9
Payments of Stock Issuance Costs	$ 0.2
At the market Offering [Member] | At The Market Equity Distribution Agreement [Member]
Subsidiary or Equity Method Investee [Line Items]
Equity Distribution Agreement, Maximum Number of Shares to be Sold (in shares)	6,033,473
Proceeds from Issuance or Sale of Equity	$ 29.2
Payments of Stock Issuance Costs	$ 0.5