Note 9 - Cash, Cash Equivalents, Investments and Restricted Cash (Tables)

9 Months Ended

Sep. 30, 2021

Notes Tables

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

	September 30,		December 31,
	2021		2020
Cash	$	212,622	$	300,609
Money market funds		13,469		34,335
Certificates of deposit		139,361		-
Corporate debt securities		369,094		249,671
Commercial paper		-		2,999
U.S. treasuries and government agency bonds		7,492		7,499
Auction-rate securities backed by student-loan notes		2,501		2,861
Total	$	744,539	$	597,974

	September 30,		December 31,
	2021		2020
Reported as:
Cash and cash equivalents	$	226,091	$	334,944
Short-term investments		515,947		260,169
Debt investment within other long-term assets		2,501		2,861
Total	$	744,539	$	597,974

Investments Classified by Contractual Maturity Date [Table Text Block]

	Amortized Cost		Fair Value
Due in less than 1 year	$	113,987	$	114,265
Due in 1 - 5 years		401,166		401,682
Due in greater than 5 years		2,620		2,501
Total	$	517,773	$	518,448

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

	September 30, 2021
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	$	13,469	$	-	$	-		$	13,469
Certificates of deposit		139,361		-		-			139,361
Corporate debt securities		368,298		1,122		(326	)		369,094
U.S. treasuries and government agency bonds		7,494		1		(3	)		7,492
Auction-rate securities backed by student-loan notes		2,620		-		(119	)		2,501
Total	$	531,242	$	1,123	$	(448	)	$	531,917

	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]

	September 30, 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	$	190,629	$	(326	)	$	-	$	-		$	190,629	$	(326	)
U.S. treasuries and government agency bonds		5,992		(3	)		-		-			5,992		(3	)
Auction-rate securities backed by student-loan notes		-		-			2,501		(119	)		2,501		(119	)
Total	$	196,621	$	(329	)	$	2,501	$	(119	)	$	199,122	$	(448	)

	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]

	September 30,		December 31,
	2021		2020
Cash and cash equivalents	$	226,091	$	334,944
Restricted cash included in other long-term assets		120		127
Total cash, cash equivalents and restricted cash reported on the Condensed Consolidated Statements of Cash Flows	$	226,211	$	335,071