Note 9 - Cash, Cash Equivalents, Investments and Restricted Cash - Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Continuous Unrealized Loss Position, Less than 12 Months	$ 20,962	$ 73,930
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(73)	(975)
Continuous Unrealized Loss Position, 12 Months or Longer	221,666	211,083
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(5,729)	(7,247)
Unrealized Loss Position, Total	242,628	285,013
Unrealized Loss Position, Accumulated Loss, Total	(5,802)	(8,222)
Corporate Debt Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months	18,084	72,943
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(68)	(973)
Continuous Unrealized Loss Position, 12 Months or Longer	212,767	202,074
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(5,559)	(6,988)
Unrealized Loss Position, Total	230,851	275,017
Unrealized Loss Position, Accumulated Loss, Total	(5,627)	(7,961)
US Treasury and Government Short-Term Debt Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months	2,878
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(5)
Continuous Unrealized Loss Position, 12 Months or Longer	7,383
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(116)
Unrealized Loss Position, Total	10,261
Unrealized Loss Position, Accumulated Loss, Total	(121)
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	1,516	1,711
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(54)	(59)
Unrealized Loss Position, Total	1,516	1,711
Unrealized Loss Position, Accumulated Loss, Total	$ (54)	$ (59)