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

12 Months Ended

Dec. 31, 2021

Notes Tables

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

	December 31,
	2021		2020
Cash	$	174,937	$	300,609
Money market funds		14,328		34,335
Certificates of deposit		141,478		-
Corporate debt securities		386,883		249,671
Commercial paper		-		2,999
U.S. treasuries and government agency bonds		7,456		7,499
Auction-rate securities backed by student-loan notes		2,401		2,861
Total	$	727,483	$	597,974

	December 31,
	2021		2020
Reported as:
Cash and cash equivalents	$	189,265	$	334,944
Short-term investments		535,817		260,169
Investment within other long-term assets		2,401		2,861
Total	$	727,483	$	597,974

Investments Classified by Contractual Maturity Date [Table Text Block]

	Amortized Cost		Fair Value
Due in less than 1 year	$	123,204	$	123,381
Due in 1 - 5 years		413,850		412,436
Due in greater than 5 years		2,520		2,401
Total	$	539,574	$	538,218

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

	December 31, 2021
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	$	14,328	$	-	$	-		$	14,328
Certificates of deposit		141,478		-		-			141,478
Corporate debt securities		388,081		570		(1,768	)		386,883
U.S. treasuries and government agency bonds		7,495		-		(39	)		7,456
Auction-rate securities backed by student-loan notes		2,520		-		(119	)		2,401
Total	$	553,902	$	570	$	(1,926	)	$	552,546

	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

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

	December 31, 2021
	Less than 12 Months					Greater than 12 Months					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Corporate debt securities	$	285,954	$	(1,765	)	$	4,760	$	(3	)	$	290,714	$	(1,768	)
U.S. treasuries and government agency bonds		7,456		(39	)		-		-			7,456		(39	)
Auction-rate securities backed by student-loan notes		-		-			2,401		(119	)		2,401		(119	)
Total	$	293,410	$	(1,804	)	$	7,161	$	(122	)	$	300,571	$	(1,926	)

	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	)

Restrictions on Cash and Cash Equivalents [Table Text Block]

	December 31,
	2021		2020
Cash and cash equivalents	$	189,265	$	334,944
Restricted cash included in other long-term assets		124		127
Total cash, cash equivalents and restricted cash reported on the Consolidated Statements of Cash Flows	$	189,389	$	335,071