Note 13 - Subsequent Events (Details Textual) - USD ($) $ / shares in Thousands		1 Months Ended	3 Months Ended	6 Months Ended
	Jul. 07, 2021	Jul. 31, 2021	Jun. 30, 2021	Jun. 30, 2021	Jun. 30, 2020	Apr. 02, 2021	Dec. 31, 2020
Proceeds from Issuance of Common Stock			$ 349,000	$ 360,000
Stock Issued During Period, Shares, New Issues (in shares)			108,879
Common Stock, No Par Value (in dollars per share)			$ 0	$ 0			$ 0
At-the-market Offering Program [Member]
Equity Offering, Maximum Offering Amount						$ 25,000,000.0
At-the-market Offering Program [Member] | Subsequent Event [Member]
Equity Offering, Maximum Offering Amount	$ 50,000,000.0
Equity Offering, Maximum Offering Amount, Additional Amount Authorized	$ 25,000,000.0
Proceeds from Issuance of Common Stock		$ 31,800,000
Stock Issued During Period, Shares, New Issues (in shares)		6,793,798
Common Stock, No Par Value (in dollars per share)		$ 0