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

3 Months Ended

Mar. 31, 2021

Notes Tables

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

	March 31,		December 31,
	2021		2020
Cash	$	197,744	$	300,609
Money market funds		20,624		34,335
Certificates of deposit		106,763		-
Corporate debt securities		306,201		249,671
Commercial paper		-		2,999
U.S. treasuries and government agency bonds		7,491		7,499
Auction-rate securities backed by student-loan notes		2,820		2,861
Total	$	641,643	$	597,974

	March 31,		December 31,
	2021		2020
Reported as:
Cash and cash equivalents		218,368		334,944
Short-term investments		420,455		260,169
Debt investment within other long-term assets		2,820		2,861
Total	$	641,643	$	597,974

Investments Classified by Contractual Maturity Date [Table Text Block]

	Amortized Cost		Fair Value
Due in less than 1 year	$	89,085	$	89,289
Due in 1 - 5 years		330,053		331,166
Due in greater than 5 years		2,995		2,820
Total	$	422,133	$	423,275

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

	March 31, 2021
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	$	20,624	$	-	$	-		$	20,624
Certificates of deposit		106,763		-		-			106,763
Corporate debt securities		304,876		1,611		(286	)		306,201
U.S. treasuries and government agency bonds		7,499		-		(8	)		7,491
Auction-rate securities backed by student-loan notes		2,995		-		(175	)		2,820
Total	$	442,757	$	1,611	$	(469	)	$	443,899

	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]

	March 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	$	152,871	$	(286	)	$	-	$	-		$	152,871	$	(286	)
U.S. treasuries and government agency bonds		7,491		(8	)		-		-			7,491		(8	)
Auction-rate securities backed by student-loan notes		-		-			2,820		(175	)		2,820		(175	)
Total	$	160,362	$	(294	)	$	2,820	$	(175	)	$	163,182	$	(469	)

	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]

	March 31,		December 31,
	2021		2020
Cash and cash equivalents	$	218,368	$	334,944
Restricted cash included in other long-term assets		119		127
Total cash, cash equivalents and restricted cash reported on the Condensed Consolidated Statements of Cash Flows	$	218,487	$	335,071