Note 4 - Cash, Cash Equivalents and Restricted Cash (Details Textual) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Average Reserve Balances Required to be Maintained with Federal Bank	$ 0	$ 60
Margin Deposit Assets	31,900	34,700
Restricted Cash, Total	1,000	9,300
Bank [Member]
Restricted Cash, Total	$ 8,000	$ 11,900