Note 3 - Investment Securities (Tables)

9 Months Ended

Sep. 30, 2023

Notes Tables

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

	September 30, 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 October 2023 and March 2024) (held-to-maturity)	$	78,257	$	10	$	243	$	78,024
Total short-term investment securities	$	78,257	$	10	$	243	$	78,024

	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