Note 4 - Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2021

Notes Tables

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

	June 30, 2021
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
	(Dollars in thousands)
Debt security type:
Corporate bonds	$	30,472	$	—	$	(10	)	$	30,707
Commercial paper		11,465		—		—			11,465
Money market funds		17,053		—		—			17,053
Foreign issuers		2,841		—		(1	)		2,849
Municipal bonds		920		—		—			938
Total debt securities available for sale	$	62,751	$	—	$	(11	)	$	63,012

Investments Classified by Contractual Maturity Date [Table Text Block]

	June 30, 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	$	30,707	$	(10	)	$	—	$	—
Commercial paper		11,465		—			—		—
Money market funds		17,053		—			—		—
Foreign issuers		2,849		(1	)		—		—
Municipal bonds		938		—			—		—
Total debt securities available for sale	$	63,012	$	(11	)	$	—	$	—