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

3 Months Ended

Mar. 31, 2022

Notes Tables

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

	March 31,		December 31,
	2022		2021
Cash	$	228,236	$	174,937
Money market funds		32,368		14,328
Certificates of deposit		141,887		141,478
Corporate debt securities		363,694		386,883
U.S. treasuries and government agency bonds		7,327		7,456
Auction-rate securities backed by student-loan notes		2,376		2,401
Total	$	775,888	$	727,483

	March 31,		December 31,
	2022		2021
Reported as:
Cash and cash equivalents	$	260,604	$	189,265
Short-term investments		512,908		535,817
Investment within other long-term assets		2,376		2,401
Total	$	775,888	$	727,483

Investments Classified by Contractual Maturity Date [Table Text Block]

	Amortized Cost		Fair Value
Due in less than 1 year	$	250,562	$	249,994
Due in 1 - 5 years		269,548		262,914
Due in greater than 5 years		2,495		2,376
Total	$	522,605	$	515,284

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

	March 31, 2022
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	$	32,368	$	-	$	-		$	32,368
Certificates of deposit		141,887		-		-			141,887
Corporate debt securities		370,728		97		(7,131	)		363,694
U.S. treasuries and government agency bonds		7,495		-		(168	)		7,327
Auction-rate securities backed by student-loan notes		2,495		-		(119	)		2,376
Total	$	554,973	$	97	$	(7,418	)	$	547,652

	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

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

	March 31, 2022
	Less than 12 Months					Greater than 12 Months					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Corporate debt securities	$	315,366	$	(7,045	)	$	12,950	$	(86	)	$	328,316	$	(7,131	)
U.S. treasuries and government agency bonds		7,327		(168	)		-		-			7,327		(168	)
Auction-rate securities backed by student-loan notes		-		-			2,376		(119	)		2,376		(119	)
Total	$	322,693	$	(7,213	)	$	15,326	$	(205	)	$	338,019	$	(7,418	)

	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	)

Restrictions on Cash and Cash Equivalents [Table Text Block]

	March 31,		December 31,
	2022		2021
Cash and cash equivalents	$	260,604	$	189,265
Restricted cash included in other long-term assets		122		124
Total cash, cash equivalents and restricted cash reported on the Condensed Consolidated Statements of Cash Flows	$	260,726	$	189,389