Note 9 - Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2017

Notes Tables

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

	Fair Value Measurement at March 31, 2017
			Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
	Total		Level 1		Level 2		Level 3
Money market funds	$	8,274	$	8,274	$	-	$	-
Certificates of deposit		7,256		-		7,256		-
Corporate debt securities		170,389		-		170,389		-
U.S. treasuries and government agency bonds		24,170		-		24,170		-
Auction-rate securities backed by student-loan notes		5,342		-		-		5,342
Mutual funds under deferred compensation plan		13,514		13,514		-		-
Total	$	228,945	$	21,788	$	201,815	$	5,342

	Fair Value Measurement at December 31, 2016
			Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
	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		(12	)
Balance at March 31, 2017	$	5,342

Schedule Of Level 3 Assumptions [Table Text Block]

	March 31,			December 31,
	2017			2016
Time-to-liquidity (months)		24			24
Discount rate	4.2%	-	9.2%	4.3%	-	9.3%