Note 9 - Cash Equivalents, Investments and Restricted Cash - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Amortized Cost	$ 442,757	$ 295,444
Unrealized Gains	1,611	2,179
Unrealized Losses	(469)	(258)
Total Fair Value	443,899	297,365
Money Market Funds [Member]
Amortized Cost	20,624	34,335
Unrealized Gains	0	0
Unrealized Losses	0	0
Total Fair Value	20,624	34,335
Certificates of Deposit [Member]
Amortized Cost	106,763
Unrealized Gains	0
Unrealized Losses	0
Total Fair Value	106,763
Corporate Debt Securities [Member]
Amortized Cost	304,876	247,591
Unrealized Gains	1,611	2,177
Unrealized Losses	(286)	(97)
Total Fair Value	306,201	249,671
Commercial Paper [Member]
Amortized Cost		2,999
Unrealized Gains		0
Unrealized Losses		0
Total Fair Value		2,999
US Government Agencies Short-term Debt Securities [Member]
Amortized Cost	7,499	7,499
Unrealized Gains	0	2
Unrealized Losses	(8)	(2)
Total Fair Value	7,491	7,499
Auction Rate Securities [Member]
Amortized Cost	2,995	3,020
Unrealized Gains	0	0
Unrealized Losses	(175)	(159)
Total Fair Value	$ 2,820	$ 2,861

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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