Note 6 - Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2020

Notes Tables

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

	March 31, 2020
(in thousands)	Cost		Unrealized Gains		Unrealized Losses			Fair Value
U.S. municipal securities	$	12,704	$	19		(14	)	$	12,709
Corporate debt securities		35,100		45		(239	)		34,906
U.S. government agency securities		20,801		61		-			20,862
Certificates of deposit/time deposits		3,697		31		(2	)		3,726
Commercial paper		2,969		11		-			2,980
Total marketable securities	$	75,271	$	167	$	(255	)	$	75,183

	December 31, 2019
(in thousands)	Cost		Unrealized Gains		Unrealized Losses			Fair Value
U.S. municipal securities	$	10,204	$	9	$	(3	)	$	10,210
Corporate debt securities		26,944		80		(12	)		27,012
U.S. government agency securities		6,274		1		(7	)		6,268
Certificates of deposit/time deposits		1,484		22		-			1,506
Commercial paper		3,491		-		-			3,491
Total marketable securities	$	48,397	$	112	$	(22	)	$	48,487

Investments Classified by Contractual Maturity Date [Table Text Block]

	March 31,
(in thousands)	2020
Due in one year or less	$	38,194
Due after one year through five years		37,077
Total marketable securities	$	75,271