Note 4 - Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2021

Notes Tables

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

	September 30, 2021
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
	(Dollars in thousands)
Debt security type:
Corporate bonds	$	30,963	$	—	$	(9	)	$	31,157
Commercial paper		11,471		—		—			11,471
Foreign issuers		2,826		—					2,851
Total debt securities available for sale	$	45,260	$	—	$	(9	)	$	45,479

Investments Classified by Contractual Maturity Date [Table Text Block]

	September 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	$	31,157	$	(9	)	$	—	$	—
Commercial paper		11,471		—			—		—
Foreign issuers		2,851		—			—		—
Total debt securities available for sale	$	45,479	$	(9	)	$	—	$	—