Note 3 - Investment Securities (Tables)

12 Months Ended

Dec. 31, 2023

Notes Tables

Debt Securities, Held-to-Maturity [Table Text Block]

	December 31, 2023
	Amortized		Gross		Gross
	cost, as		unrealized		unrealized		Estimated
(in thousands)	adjusted		holding gains		holding losses		fair value
Short-term investments:
Obligations of domestic governmental agencies (maturing between January 2024 and June 2024) (held-to-maturity)	$	124,575	$	30	$	53	$	124,552
Total short-term investment securities	$	124,575	$	30	$	53	$	124,552

	December 31, 2022
	Amortized		Gross		Gross
	cost, as		unrealized		unrealized		Estimated
	adjusted		holding gains		holding losses		fair value
Short-term investments:
Obligations of domestic governmental agencies (maturing between January 2023 and December 2023) (held-to-maturity)	$	59,374	$	—	$	1,053	$	58,321
Long-term investments:
Obligations of domestic governmental agencies (maturing between January 2024 and February 2024) (held-to-maturity)		12,404		—		429		11,975
Total short-term and long-term investment securities	$	71,778	$	—	$	1,482	$	70,296