Note 9 - Cash, Cash Equivalents, Investments and Restricted Cash - Unrealized Gains and Losses on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Amortized Cost	$ 477,020	$ 474,643
Unrealized Gains	122	18
Unrealized Losses	(5,802)	(8,222)
Total Fair Value	471,340	466,439
Total Fair Value	471,340	466,439
Money Market Funds [Member]
Amortized Cost	41,226	15,462
Unrealized Gains	0	0
Unrealized Losses	0	0
Total Fair Value	41,226	15,462
Total Fair Value	41,226	15,462
Certificates of Deposit [Member]
Amortized Cost	131,042	130,467
Unrealized Gains	0	0
Unrealized Losses	0	0
Total Fair Value	131,042	130,467
Total Fair Value	131,042	130,467
Corporate Debt Securities [Member]
Amortized Cost	249,743	300,529
Unrealized Gains	39	18
Unrealized Losses	(5,627)	(7,961)
Total Fair Value	244,155	292,586
Total Fair Value	244,155	292,586
Commercial Paper [Member]
Amortized Cost	18,163	17,928
Unrealized Gains	0	0
Unrealized Losses	0	0
Total Fair Value	18,163	17,928
Total Fair Value	18,163	17,928
US Government Agencies Short-Term Debt Securities [Member]
Amortized Cost	35,276	8,487
Unrealized Gains	83	0
Unrealized Losses	(121)	(202)
Total Fair Value	35,238	8,285
Total Fair Value	35,238	8,285
Auction Rate Securities [Member]
Amortized Cost	1,570	1,770
Unrealized Gains	0	0
Unrealized Losses	(54)	(59)
Total Fair Value	1,516	1,711
Total Fair Value	$ 1,516	$ 1,711