Note 9 - Cash, Cash Equivalents, Investments and Restricted Cash - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Amortized Cost	$ 548,516	$ 553,902
Unrealized Gains	9	570
Unrealized Losses	(8,902)	(1,926)
Total Fair Value	539,623	552,546
Money Market Funds [Member]
Amortized Cost	68,392	14,328
Unrealized Gains	0	0
Unrealized Losses	0	0
Total Fair Value	68,392	14,328
Certificates of Deposit [Member]
Amortized Cost	134,374	141,478
Unrealized Gains	0	0
Unrealized Losses	0	0
Total Fair Value	134,374	141,478
Corporate Debt Securities [Member]
Amortized Cost	335,934	388,081
Unrealized Gains	9	570
Unrealized Losses	(8,585)	(1,768)
Total Fair Value	327,358	386,883
US Government Agencies Short-Term Debt Securities [Member]
Amortized Cost	7,496	7,495
Unrealized Gains	0	0
Unrealized Losses	(216)	(39)
Total Fair Value	7,280	7,456
Auction Rate Securities [Member]
Amortized Cost	2,320	2,520
Unrealized Gains	0	0
Unrealized Losses	(101)	(119)
Total Fair Value	$ 2,219	$ 2,401