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

12 Months Ended

Dec. 31, 2018

Notes Tables

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

	December 31,
	2018		2017
Cash, cash equivalents and investments:
Cash	$	131,569	$	75,125
Money market funds		41,135		7,134
Corporate debt securities		170,909		203,807
U.S. treasuries and government agency bonds		32,068		13,024
Certificates of deposit		1,600		-
Auction-rate securities backed by student-loan notes		3,241		5,256
Total	$	380,522	$	304,346

	December 31,
	2018		2017
Reported as:
Cash and cash equivalents	$	172,704	$	82,759
Short-term investments		204,577		216,331
Long-term investments		3,241		5,256
Total	$	380,522	$	304,346

Investments Classified by Contractual Maturity Date [Table Text Block]

	December 31,
	2018		2017
Due in less than 1 year	$	125,845	$	89,399
Due in 1 - 5 years		78,732		126,932
Due in greater than 5 years		3,241		5,256
Total	$	207,818	$	221,587

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

	December 31, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Total Fair Value		Fair Value of Investments in Unrealized Loss Position
Money market funds	$	41,135	$	-	$	-		$	41,135	$	-
Corporate debt securities		172,288		7		(1,386	)		170,909		166,204
U.S. treasuries and government agency bonds		32,207		2		(141	)		32,068		28,507
Certificates of deposit		1,600		-		-			1,600		-
Auction-rate securities backed by student-loan notes		3,570		-		(329	)		3,241		3,241
Total	$	250,800	$	9	$	(1,856	)	$	248,953	$	197,952

	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

Restrictions on Cash and Cash Equivalents [Table Text Block]

	December 31,
	2018		2017
Cash and cash equivalents	$	172,704	$	82,759
Restricted cash included in other long-term assets		114		115
Total cash, cash equivalents and restricted cash reported in the Consolidated Statements of Cash Flows	$	172,818	$	82,874