Note 9 - Cash, Cash Equivalents, Investments and Restricted Cash - Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Continuous Unrealized Loss Position, Less than 12 Months	$ 136,897	$ 73,930
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(633)	(975)
Continuous Unrealized Loss Position, 12 Months or Longer	155,677	211,083
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(4,203)	(7,247)
Unrealized Loss Position, Total	292,574	285,013
Unrealized Loss Position, Accumulated Loss, Total	(4,836)	(8,222)
Corporate Debt Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months	30,126	72,943
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(103)	(973)
Continuous Unrealized Loss Position, 12 Months or Longer	151,567	202,074
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(4,164)	(6,988)
Unrealized Loss Position, Total	181,693	275,017
Unrealized Loss Position, Accumulated Loss, Total	(4,267)	(7,961)
US Treasury and Government Short-Term Debt Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months	106,771
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(530)
Continuous Unrealized Loss Position, 12 Months or Longer	3,461
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(38)
Unrealized Loss Position, Total	110,232
Unrealized Loss Position, Accumulated Loss, Total	(568)
US Government Agencies Short-Term Debt Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months		987
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(2)
Continuous Unrealized Loss Position, 12 Months or Longer		7,298
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(200)
Unrealized Loss Position, Total		8,285
Unrealized Loss Position, Accumulated Loss, Total		(202)
Auction Rate Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months	0	0
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Continuous Unrealized Loss Position, 12 Months or Longer	649	1,711
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1)	(59)
Unrealized Loss Position, Total	649	1,711
Unrealized Loss Position, Accumulated Loss, Total	$ (1)	$ (59)