Note 9 - Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2017

Notes Tables

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

	Fair Value Measurement at June 30, 2017
	Total		Level 1		Level 2		Level 3
Money market funds	$	8,944	$	8,944	$	-	$	-
Certificates of deposit		7,378		-		7,378		-
Corporate debt securities		181,269		-		181,269		-
U.S. treasuries and government agency bonds		17,914		-		17,914		-
Auction-rate securities backed by student-loan notes		5,348		-		-		5,348
Mutual funds under deferred compensation plan		14,239		14,239		-		-
Total	$	235,092	$	23,183	$	206,561	$	5,348

	Fair Value Measurement at December 31, 2016
	Total		Level 1		Level 2		Level 3
Money market funds	$	24,956	$	24,956	$	-	$	-
Corporate debt securities		109,644		-		109,644		-
U.S. treasuries and government agency bonds		45,877		-		45,877		-
Auction-rate securities backed by student-loan notes		5,354		-		-		5,354
Mutual funds under deferred compensation plan		12,108		12,108		-		-
Total	$	197,939	$	37,064	$	155,521	$	5,354

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

Balance at January 1, 2017	$	5,354
Change in unrealized loss included in other comprehensive income		(6	)
Balance at June 30, 2017	$	5,348

Schedule Of Level 3 Assumptions [Table Text Block]

	June 30,			December 31,
	2017			2016
Time-to-liquidity (months)		2 4			2 4
Discount rate	4.2%	-	9.2%	4.3%	-	9.3%