Note 3 - U.S. Treasury Securities, Available-for-sale - Available-for-sale- Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
U.S. Treasury securities, available for sale, amortized cost	$ 100,412	$ 148,803
Pledged assets, available for sale	100,551	148,820
U.S. Treasury Note, 4.625%, 6/30/2026 Maturity [Member]
U.S. Treasury securities, available for sale, amortized cost	100,412
Gross unrealized gains	139
Gross unrealized losses	0
Pledged assets, available for sale	100,551
US Treasury Securities [Member]
U.S. Treasury securities, available for sale, amortized cost	100,412	148,803
Gross unrealized gains	139	17
Gross unrealized losses	0	0
Pledged assets, available for sale	$ 100,551	148,820
Treasury Bill 1/2/2024 Maturity [Member]
U.S. Treasury securities, available for sale, amortized cost		49,671
Gross unrealized gains		9
Gross unrealized losses		0
Pledged assets, available for sale		49,680
Treasury Bill 2/15/2024 Maturity [Member]
U.S. Treasury securities, available for sale, amortized cost		49,992
Gross unrealized gains		8
Gross unrealized losses		0
Pledged assets, available for sale		50,000
Treasury Bill 4/30/2024 Maturity [Member]
U.S. Treasury securities, available for sale, amortized cost		49,140
Gross unrealized gains		0
Gross unrealized losses		0
Pledged assets, available for sale		$ 49,140