Note 3 - U.S. Treasury Securities, Available-for-sale - Available-for-sale- Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair value	$ 99,496	$ 148,820
Treasury Bill 4/30/2024 Maturity [Member]
Amortized cost	49,791	49,140
Gross unrealized gains	0	0
Gross unrealized losses	(24)	0
Fair value	49,767	49,140
Gross unrealized losses	24	0
Treasury Note 5/31/2024 Maturity [Member]
Amortized cost	49,735
Gross unrealized gains	0
Gross unrealized losses	(6)
Fair value	49,729
Gross unrealized losses	6
US Treasury Securities [Member]
Amortized cost	99,526	148,803
Gross unrealized gains	0	17
Gross unrealized losses	(30)	0
Fair value	99,496	148,820
Gross unrealized losses	$ 30	0
Treasury Bill 1/2/2024 Maturity [Member]
Amortized cost		49,671
Gross unrealized gains		9
Gross unrealized losses		0
Fair value		49,680
Gross unrealized losses		0
Treasury Bill 2/15/2024 Maturity [Member]
Amortized cost		49,992
Gross unrealized gains		8
Gross unrealized losses		0
Fair value		50,000
Gross unrealized losses		$ 0