Note 6 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Feb. 18, 2021
Subsidiary or Equity Method Investee [Line Items]
Share-Based Payment Arrangement, Expense	$ 1.5	$ 1.3	$ 2.7	$ 2.5
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 9.5		$ 9.5
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)			1 year 8 months 12 days
Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation (in shares)			404,514
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
Proceeds from Issuance or Sale of Equity	$ 14.0		$ 25.9
Payments of Stock Issuance Costs	$ 0.2		$ 0.4
Common stock issued under ATM program , shares	2,080,060		4,253,334
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]
Equity Distribution Agreement, Maximum Number of Shares to be Sold (in shares)	8,113,533		8,113,533
Proceeds from Issuance or Sale of Equity			$ 43.2
Payments of Stock Issuance Costs			$ 0.7