Note 10 - Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2023

Notes Tables

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

	September 30, 2023
	Total		Level 1		Level 2		Level 3
Money market funds	$	43,854	$	43,854	$	-	$	-
Certificates of deposit		123,368		-		123,368		-
Corporate debt securities		130,614		-		130,614		-
Commercial paper		4,976		-		4,976		-
U.S. treasuries and government agency bonds		362,165		-		362,165		-
Auction-rate securities backed by student-loan notes		600		-		-		600
Mutual funds and money market funds under deferred compensation plan		49,825		49,825		-		-
Total	$	715,402	$	93,679	$	621,123	$	600

	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