Note 11 - Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2019

Notes Tables

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

	Fair Value Measurement at March 31, 2019
	Total		Level 1		Level 2		Level 3
Money market funds	$	56,082	$	56,082	$	-	$	-
Corporate debt securities		143,453		-		143,453		-
U.S. treasuries and government agency bonds		32,202		-		32,202		-
Certificates of deposit		1,600				1,600
Auction-rate securities backed by student-loan notes		3,290		-		-		3,290
Mutual funds and money market funds under deferred compensation plan		20,873		20,873		-		-
Total	$	257,500	$	76,955	$	177,255	$	3,290

	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		49
Balance at March 31, 2019	$	3,290

Schedule Of Level 3 Assumptions [Table Text Block]

	March 31,			December 31,
	2019			2018
Time-to-liquidity (years)	2	-	3	2	-	3
Discount rate	4.6%	-	9.9%	4.9%	-	10.1%