Note 6 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Feb. 18, 2021
Subsidiary or Equity Method Investee [Line Items]
Share-Based Payment Arrangement, Expense	$ 2.4	$ 1.8	$ 5.1	$ 4.3
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 9.0		$ 9.0
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)			1 year 6 months
Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation (in shares)			404,514,000
Share-Based Payment Arrangement, Decrease for Tax Withholding Obligation			$ 2.0
Shares Withheld for Tax Withholding Obligation, Price Per Share (in dollars per share)	$ 5.03		$ 5.03
Equity Distribution Agreement, Maximum Number of Shares to be Sold (in shares)	8,113,553,000		8,113,553,000
Stock Issued During Period, Shares, New Issues (in shares)			4,253,334,000
Proceeds from Issuance or Sale of Equity			$ 25.9
Payments of Stock Issuance Costs			$ 0.4
Common stock issued under ATM program, net shares		1,176,861	4,253,334	1,176,861
At the market Offering [Member]
Subsidiary or Equity Method Investee [Line Items]
Equity Distribution Agreement, Maximum Number of Shares to be Sold (in shares)					60,000,000
At the market Offering [Member] | At The Market Equity Distribution Agreement [Member]
Subsidiary or Equity Method Investee [Line Items]
Proceeds from Issuance or Sale of Equity			$ 43.2
Payments of Stock Issuance Costs			$ 0.7