Note 7 - Capital Stock - Issuance of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Issuance of common stock pursuant to public offerings, net (in shares)									3,885,048	20,165,635
Issuance of common stock pursuant to public offerings, net									$ 40,580	$ 514,059	$ 71,050
At the Market Offering Program [Member]
Price per share (in dollars per share)	$ 10.45	$ 0	$ 0	$ 0	$ 24.34	$ 24.70	$ 27.00	$ 25.50	$ 10.45	$ 24.34
Issuance of common stock pursuant to public offerings, net (in shares)	3,885,048	0	0	0	4,734,940	7,163,668	4,617,418	61,610
Issuance of common stock pursuant to public offerings, net	$ 40,580	$ 0	$ 0	$ 0	$ 115,398	$ 177,007	$ 124,746	$ 1,572
Follow-on Offerings [Member]
Price per share (in dollars per share)				$ 26.55
Issuance of common stock pursuant to public offerings, net (in shares)				3,588,000
Issuance of common stock pursuant to public offerings, net				$ 95,336