Note 11 - Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2019

Notes Tables

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

	Fair Value Measurement at September 30, 2019
	Total		Level 1		Level 2		Level 3
Money market funds	$	39,982	$	39,982	$	-	$	-
Corporate debt securities		195,667		-		195,667		-
U.S. treasuries and government agency bonds		20,350		-		20,350		-
Auction-rate securities backed by student-loan notes		3,264		-		-		3,264
Mutual funds and money market funds under deferred compensation plan		19,968		19,968		-		-
Total	$	279,231	$	59,950	$	216,017	$	3,264

	Fair Value Measurement at December 31, 2018
	Total		Level 1		Level 2		Level 3
Money market funds	$	41,135	$	41,135	$	-	$	-
Corporate debt securities		170,909		-		170,909		-
U.S. treasuries and government agency bonds		32,068		-		32,068		-
Certificates of deposit		1,600		-		1,600		-
Auction-rate securities backed by student-loan notes		3,241		-		-		3,241
Mutual funds and money market funds under deferred compensation plan		18,867		18,867		-		-
Total	$	267,820	$	60,002	$	204,577	$	3,241

Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]

Balance at January 1, 2019	$	3,241
Change in unrealized gain included in other comprehensive income		148
Sale and settlement at par		(125	)
Balance at September 30, 2019	$	3,264

Schedule Of Level 3 Assumptions [Table Text Block]

	September 30,			December 31,
	2019			2018
Time-to-liquidity (in years)	2	-	3	2	-	3
Discount rate	3.7%	-	7.9%	4.9%	-	10.1%