Note 9 - Cash, Cash Equivalents, Investments and Restricted Cash - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Amortized Cost	$ 554,973	$ 553,902
Unrealized Gains	97	570
Unrealized Losses	(7,418)	(1,926)
Total Fair Value	547,652	552,546
Money Market Funds [Member]
Amortized Cost	32,368	14,328
Unrealized Gains	0	0
Unrealized Losses	0	0
Total Fair Value	32,368	14,328
Certificates of Deposit [Member]
Amortized Cost	141,887	141,478
Unrealized Gains	0	0
Unrealized Losses	0	0
Total Fair Value	141,887	141,478
Corporate Debt Securities [Member]
Amortized Cost	370,728	388,081
Unrealized Gains	97	570
Unrealized Losses	(7,131)	(1,768)
Total Fair Value	363,694	386,883
US Government Agencies Short-Term Debt Securities [Member]
Amortized Cost	7,495	7,495
Unrealized Gains	0	0
Unrealized Losses	(168)	(39)
Total Fair Value	7,327	7,456
Auction Rate Securities [Member]
Amortized Cost	2,495	2,520
Unrealized Gains	0	0
Unrealized Losses	(119)	(119)
Total Fair Value	$ 2,376	$ 2,401