Note 9 - Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2017

Notes Tables

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

	Fair Value Measurement at September 30, 2017
	Total		Level 1		Level 2		Level 3
Money market funds	$	11,250	$	11,250	$	-	$	-
Corporate debt securities		180,551		-		180,551		-
U.S. treasuries and government agency bonds		16,123		-		16,123		-
Auction-rate securities backed by student-loan notes		5,368		-		-		5,368
Mutual funds under deferred compensation plan		13,097		13,097		-		-
Total	$	226,389	$	24,347	$	196,674	$	5,368

	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 gain included in other comprehensive income		14
Balance at September 30, 2017	$	5,368

Schedule Of Level 3 Assumptions [Table Text Block]

	September 30,			December 31,
	2017			2016
Time-to-liquidity (months)		24			24
Discount rate	40%	-	9.0%	4.3%	-	9.3%