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

6 Months Ended

Jun. 30, 2020

Notes Tables

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

	June 30,		December 31,
	2020		2019
Cash, cash equivalents and investments:
Cash	$	130,397	$	144,860
Money market funds		26,086		28,100
Corporate debt securities		333,622		260,950
Commercial paper		7,968		1,994
U.S. treasuries and government agency bonds		14,250		19,493
Auction-rate securities backed by student-loan notes		3,032		3,138
Total	$	515,355	$	458,535

	June 30,		December 31,
	2020		2019
Reported as:
Cash and cash equivalents	$	156,483	$	172,960
Short-term investments		355,840		282,437
Long-term investments		3,032		3,138
Total	$	515,355	$	458,535

Investments Classified by Contractual Maturity Date [Table Text Block]

	Amortized Cost		Fair Value
Due in less than 1 year	$	168,329	$	169,259
Due in 1 - 5 years		183,611		186,581
Due in greater than 5 years		3,195		3,032
Total	$	355,135	$	358,872

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

	June 30, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	$	26,086	$	-	$	-		$	26,086
Corporate debt securities		329,755		3,930		(63	)		333,622
Commercial paper		7,936		32		-			7,968
U.S. treasuries and government agency bonds		14,249		2		(1	)		14,250
Auction-rate securities backed by student-loan notes		3,195		-		(163	)		3,032
Total	$	381,221	$	3,964	$	(227	)	$	384,958

	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]

	June 30, 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	$	23,533	$	(63	)	$	-	$	-		$	23,533	$	(63	)
U.S. treasuries and government agency bonds		2,499		(1	)		-		-			2,499		(1	)
Auction-rate securities backed by student-loan notes		-		-			3,032		(163	)		3,032		(163	)
Total	$	26,032	$	(64	)	$	3,032	$	(163	)	$	29,064	$	(227	)

	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]

	June 30,		December 31,
	2020		2019
Cash and cash equivalents	$	156,483	$	172,960
Restricted cash included in other long-term assets		118		116
Total cash, cash equivalents and restricted cash reported on the Condensed Consolidated Statements of Cash Flows	$	156,601	$	173,076