Note 3 - Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2021

Notes Tables

Debt Securities, Available-for-sale [Table Text Block]

	December 31, 2021
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
	(Dollars in thousands)
Debt security type:
Corporate bonds	$	32,302	$	—	$	(36	)	$	32,529
Commercial paper		8,891		—		—			8,891
Money market funds		3,686		—		—			3,686
Foreign issuers		1,920		—		(4	)		1,923
Total debt securities available for sale	$	46,799	$	—	$	(40	)	$	47,029

Investments Classified by Contractual Maturity Date [Table Text Block]

	December 31, 2021
	Less than 12 months					Greater than 12 months
	Fair value		Gross unrealized loss			Fair value		Gross unrealized loss
	(Dollars in thousands)
Debt security type:
Corporate bonds	$	32,529	$	(36	)	$	—	$	—
Commercial paper		8,891		—			—		—
Money market funds		3,686		—			—		—
Foreign issuers		1,923		(4	)		—		—
Total debt securities available for sale	$	47,029	$	(40	)	$	—	$	—