Note 3 - Cash, Cash Equivalents, Investments and Restricted Cash - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Amortized Cost	$ 553,902	$ 295,444
Unrealized Gains	570	2,179
Unrealized Losses	(1,926)	(258)
Total Fair Value	552,546	297,365
Money Market Funds [Member]
Amortized Cost	14,328	34,335
Unrealized Gains	0	0
Unrealized Losses	0	0
Total Fair Value	14,328	34,335
Certificates of Deposit [Member]
Amortized Cost	141,478
Unrealized Gains	0
Unrealized Losses	0
Total Fair Value	141,478
Corporate Debt Securities [Member]
Amortized Cost	388,081	247,591
Unrealized Gains	570	2,177
Unrealized Losses	(1,768)	(97)
Total Fair Value	386,883	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	7,495	7,499
Unrealized Gains	0	2
Unrealized Losses	(39)	(2)
Total Fair Value	7,456	7,499
Auction Rate Securities [Member]
Amortized Cost	2,520	3,020
Unrealized Gains	0	0
Unrealized Losses	(119)	(159)
Total Fair Value	$ 2,401	$ 2,861