Note 1 - Organization and Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands				3 Months Ended			4 Months Ended	12 Months Ended		13 Months Ended
		Mar. 07, 2023	Oct. 29, 2021	Mar. 31, 2024		Mar. 31, 2023	Oct. 28, 2021	Dec. 31, 2023		Mar. 31, 2024
Stock Issued During Period, Shares, New Issues (in shares)	[1]			1,490,075				15,880,039
Stock Issued During Period, Value, New Issues				$ 13,109	[2]	$ 31,657		$ 159,438	[2]
Proceeds from Issuance of Common Stock				$ 13,109		$ 31,657
June 2021 Equity Distribution Agreement [Member]
Equity Agreement, Maximum Number of Shares Issuable (in shares)							250,000,000
October 2021 Equity Distribution Agreement [Member]
Stock Issued During Period, Shares, New Issues (in shares)			9,742,188
Stock Issued During Period, Value, New Issues			$ 151,800
Proceeds from Issuance of Common Stock			$ 149,300
March 2023 Equity Distribution Agreement [Member]
Equity Agreement, Maximum Number of Shares Issuable (in shares)		250,000,000
Stock Issued During Period, Shares, New Issues (in shares)										14,680,114
Stock Issued During Period, Value, New Issues										$ 143,200
Proceeds from Issuance of Common Stock										$ 140,900

[1] The Company has entered into eleven equity distribution agreements, ten of which have either been terminated because all shares were sold or were replaced with a subsequent agreement.

[2] Net proceeds are net of the underwriters' discount, if applicable, and other offering costs.