Note 10 - Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2022

Notes Tables

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

	March 31, 2022
	Total		Level 1		Level 2		Level 3
Money market funds	$	32,368	$	32,368	$	-	$	-
Certificates of deposit		141,887	$	-		141,887		-
Corporate debt securities		363,694		-		363,694		-
U.S. treasuries and government agency bonds		7,327		-		7,327		-
Auction-rate securities backed by student-loan notes		2,376		-		-		2,376
Mutual funds and money market funds under deferred compensation plan		31,010		31,010		-		-
Total	$	578,662	$	63,378	$	512,908	$	2,376

	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