Note 4 - Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2022

Notes Tables

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

	March 31, 2022									December 31, 2021
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value		Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
	(Dollars in thousands)									(Dollars in thousands)
Debt security type:
Corporate bonds	$	31,002	$	—	$	(127	)	$	31,043	$	32,302	$	—	$	(36	)	$	32,529
Commercial paper		9,375		—		—			9,375		8,891		—		—			8,891
Money market funds		4,049		—		—			4,049		3,686		—		—			3,686
Foreign issuers		1,010		—		(11	)		1,005		1,920		—		(4	)		1,923
Municipal bonds		1,497		—		(4	)		1,504		—		—		—			—
Total debt securities available for sale	$	46,933	$	—	$	(142	)	$	46,976	$	46,799	$	—	$	(40	)	$	47,029

Investments Classified by Contractual Maturity Date [Table Text Block]

	March 31, 2022									December 31, 2021
	Less than 12 months					Greater than 12 months				Less than 12 months					Greater than 12 months
	Fair value		Gross unrealized loss			Fair value		Gross unrealized loss		Fair value		Gross unrealized loss			Fair value		Gross unrealized loss
	(Dollars in thousands)									(Dollars in thousands)
Debt security type:
Corporate bonds	$	31,043	$	(127	)	$	—	$	—	$	32,529	$	(36	)	$	—	$	—
Commercial paper		9,375		—			—		—		8,891		—			—		—
Money market funds		4,049		—			—		—		3,686		—			—		—
Foreign issuers		1,005		(11	)		—		—		1,923		(4	)		—		—
Municipal bonds		1,504		(4	)		—		—		—		—			—		—
Total debt securities available for sale	$	46,976	$	(142	)	$	—	$	—	$	47,029	$	(40	)	$	—	$	—