Note 3 - Cash, Cash Equivalents and Investments (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Fair Value, by Balance Sheet Grouping [Table Text Block]

	December 31,
	2017		2016
Cash, cash equivalents and investments:
Cash	$	75,125	$	87,747
Money market funds		7,134		24,956
Corporate debt securities		203,807		109,644
U.S. treasuries and government agency bonds		13,024		45,877
Auction-rate securities backed by student-loan notes		5,256		5,354
Total	$	304,346	$	273,578

	December 31,
	2017		2016
Reported as:
Cash and cash equivalents	$	82,759	$	112,703
Short-term investments		216,331		155,521
Long-term investments		5,256		5,354
Total	$	304,346	$	273,578

Investments Classified by Contractual Maturity Date [Table Text Block]

	December 31,
	2017		2016
Due in less than 1 year	$	89,399	$	47,568
Due in 1 - 5 years		126,932		107,953
Due in greater than 5 years		5,256		5,354
Total	$	221,587	$	160,875

Unrealized Gain (Loss) on Investments [Table Text Block]

	December 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Total Fair Value		Fair Value of Investments in Unrealized Loss Position
Money market funds	$	7,134	$	-	$	-		$	7,134	$	-
Corporate debt securities		204,789		17		(999	)		203,807		197,564
U.S. treasuries and government agency bonds		13,092		-		(68	)		13,024		13,024
Auction-rate securities backed by student-loan notes		5,570		-		(314	)		5,256		5,256
Total	$	230,585	$	17	$	(1,381	)	$	229,221	$	215,844

	December 31, 2016
	Amortized Cost		Unrealized Gains		Unrealized Losses			Total Fair Value		Fair Value of Investments in Unrealized Loss Position
Money market funds	$	24,956	$	-	$	-		$	24,956	$	-
Corporate debt securities		110,429		65		(850	)		109,644		91,938
U.S. treasuries and government agency bonds		45,899		-		(22	)		45,877		39,275
Auction-rate securities backed by student-loan notes		5,570		-		(216	)		5,354		5,354
Total	$	186,854	$	65	$	(1,088	)	$	185,831	$	136,567