Note 10 - Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2022

Notes Tables

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

	June 30, 2022
	Total		Level 1		Level 2		Level 3
Money market funds	$	68,392	$	68,392	$	-	$	-
Certificates of deposit		134,374		-		134,374		-
Corporate debt securities		327,358		-		327,358		-
U.S. treasuries and government agency bonds		7,280		-		7,280		-
Auction-rate securities backed by student-loan notes		2,219		-		-		2,219
Mutual funds and money market funds under deferred compensation plan		29,152		29,152		-		-
Total	$	568,775	$	97,544	$	469,012	$	2,219

	December 31, 2021
	Total		Level 1		Level 2		Level 3
Money market funds	$	14,328	$	14,328	$	-	$	-
Certificates of deposit		141,478		-		141,478		-
Corporate debt securities		386,883		-		386,883		-
U.S. treasuries and government agency bonds		7,456		-		7,456		-
Auction-rate securities backed by student-loan notes		2,401		-		-		2,401
Mutual funds and money market funds under deferred compensation plan		31,786		31,786		-		-
Total	$	584,332	$	46,114	$	535,817	$	2,401