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

12 Months Ended

Dec. 31, 2019

Notes Tables

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

	December 31,
	2019		2018
Cash, cash equivalents and investments:
Cash	$	144,860	$	131,569
Money market funds		28,100		41,135
Corporate debt securities		260,950		170,909
Commercial paper		1,994		-
U.S. treasuries and government agency bonds		19,493		32,068
Certificates of deposit		-		1,600
Auction-rate securities backed by student-loan notes		3,138		3,241
Total	$	458,535	$	380,522

	December 31,
	2019		2018
Reported as:
Cash and cash equivalents	$	172,960	$	172,704
Short-term investments		282,437		204,577
Long-term investments		3,138		3,241
Total	$	458,535	$	380,522

Investments Classified by Contractual Maturity Date [Table Text Block]

	December 31,
	2019		2018
Due in less than 1 year	$	147,532	$	125,845
Due in 1 - 5 years		134,905		78,732
Due in greater than 5 years		3,138		3,241
Total	$	285,575	$	207,818

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

	December 31, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses			Total Fair Value		Fair Value of Investments in Unrealized Loss Position
Money market funds	$	28,100	$	-	$	-		$	28,100	$	-
Corporate debt securities		260,645		383		(78	)		260,950		93,262
Commercial paper		1,994		-		-			1,994		-
U.S. treasuries and government agency bonds		19,487		7		(1	)		19,493		993
Auction-rate securities backed by student-loan notes		3,320		-		(182	)		3,138		3,138
Total	$	313,546	$	390	$	(261	)	$	313,675	$	97,393

	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

Restrictions on Cash and Cash Equivalents [Table Text Block]

	December 31,
	2019		2018
Cash and cash equivalents	$	172,960	$	172,704
Restricted cash included in other long-term assets		116		114
Total cash, cash equivalents and restricted cash reported on the Consolidated Statements of Cash Flows	$	173,076	$	172,818