Note 4 - Other Recent Business Transactions Or Events - SPAC Investment (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Apr. 01, 2023	Dec. 31, 2022
Cash and cash equivalents	$ 13,350		$ 29,101
Receivables from brokers, dealers, and clearing agencies	106,740		140,933
Other assets	3,569		3,546
Accounts payable and other liabilities	(6,217)		(11,439)
Other investments sold, not yet purchased	(18,131)		(78)
GP of the SPAC Fund's remaining investment in the SPAC Fund	$ 35,565		$ 47,287
SPAC Fund [Member]
Cash and cash equivalents		$ 257
Receivables from brokers, dealers, and clearing agencies		68,066
Other Investments, Total		40,388
Other assets		108
Accounts payable and other liabilities		(82,968)
Other investments sold, not yet purchased		(25,806)
GP of the SPAC Fund's remaining investment in the SPAC Fund		$ 45