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

12 Months Ended

Dec. 31, 2020

Notes Tables

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

	December 31,
	2020		2019
Cash	$	300,609	$	144,860
Money market funds		34,335		28,100
Corporate debt securities		249,671		260,950
Commercial paper		2,999		1,994
U.S. treasuries and government agency bonds		7,499		19,493
Auction-rate securities backed by student-loan notes		2,861		3,138
Total	$	597,974	$	458,535

	December 31,
	2020		2019
Reported as:
Cash and cash equivalents	$	334,944	$	172,960
Short-term investments		260,169		282,437
Investment within other long-term assets		2,861		3,138
Total	$	597,974	$	458,535

Investments Classified by Contractual Maturity Date [Table Text Block]

	Amortized Cost		Fair Value
Due in less than 1 year	$	97,773	$	98,036
Due in 1 - 5 years		160,316		162,133
Due in greater than 5 years		3,020		2,861
Total	$	261,109	$	263,030

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

	December 31, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	$	34,335	$	-	$	-		$	34,335
Corporate debt securities		247,591		2,177		(97	)		249,671
Commercial paper		2,999		-		-			2,999
U.S. treasuries and government agency bonds		7,499		2		(2	)		7,499
Auction-rate securities backed by student-loan notes		3,020		-		(159	)		2,861
Total	$	295,444	$	2,179	$	(258	)	$	297,365

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

Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value [Table Text Block]

	December 31, 2020
	Less than 12 Months					Greater than 12 Months					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Corporate debt securities	$	59,144	$	(97	)	$	-	$	-		$	59,144	$	(97	)
U.S. treasuries and government agency bonds		5,998		(2	)		-		-			5,998		(2	)
Auction-rate securities backed by student-loan notes		-		-			2,861		(159	)		2,861		(159	)
Total	$	65,142	$	(99	)	$	2,861	$	(159	)	$	68,003	$	(258	)

	December 31, 2019
	Less than 12 Months					Greater than 12 Months					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Corporate debt securities	$	82,126	$	(63	)	$	11,136	$	(15	)	$	93,262	$	(78	)
U.S. treasuries and government agency bonds		993		(1	)		-		-			993		(1	)
Auction-rate securities backed by student-loan notes		-		-			3,138		(182	)		3,138		(182	)
Total	$	83,119	$	(64	)	$	14,274	$	(197	)	$	97,393	$	(261	)

Restrictions on Cash and Cash Equivalents [Table Text Block]

	December 31,
	2020		2019
Cash and cash equivalents	$	334,944	$	172,960
Restricted cash included in other long-term assets		127		116
Total cash, cash equivalents and restricted cash reported on the Consolidated Statements of Cash Flows	$	335,071	$	173,076