Note 10 - Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2023

Notes Tables

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]

	June 30, 2023
	Total		Level 1		Level 2		Level 3
Money market funds	$	47,814	$	47,814	$	-	$	-
Certificates of deposit		124,043		-		124,043		-
Corporate debt securities		183,695		-		183,695		-
Commercial paper		11,376		-		11,376
U.S. treasuries and government agency bonds		114,413		-		114,413		-
Auction-rate securities backed by student-loan notes		649		-		-		649
Mutual funds and money market funds under deferred compensation plan		49,578		49,578		-		-
Total	$	531,568	$	97,392	$	433,527	$	649

	December 31, 2022
	Total		Level 1		Level 2		Level 3
Money market funds	$	15,462	$	15,462	$	-	$	-
Certificates of deposit		130,467		-		130,467		-
Corporate debt securities		292,586		-		292,586		-
Commercial paper		17,928		-		17,928		-
U.S. treasuries and government agency bonds		8,285		-		8,285		-
Auction-rate securities backed by student-loan notes		1,711		-		-		1,711
Mutual funds and money market funds under deferred compensation plan		43,933		43,933		-		-
Total	$	510,372	$	59,395	$	449,266	$	1,711