Note 9 - Cash, Cash Equivalents, Investments and Restricted Cash - Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Continuous Unrealized Loss Position, Less than 12 Months	$ 266,480	$ 73,930
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(772)	(975)
Continuous Unrealized Loss Position, 12 Months or Longer	99,230	211,083
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(2,755)	(7,247)
Unrealized Loss Position, Total	365,710	285,013
Unrealized Loss Position, Accumulated Loss, Total	(3,527)	(8,222)
Corporate Debt Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months	29,476	72,943
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(79)	(973)
Continuous Unrealized Loss Position, 12 Months or Longer	97,133	202,074
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(2,752)	(6,988)
Unrealized Loss Position, Total	126,609	275,017
Unrealized Loss Position, Accumulated Loss, Total	(2,831)	(7,961)
US Treasury and Government Short-Term Debt Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months	237,004
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(693)
Continuous Unrealized Loss Position, 12 Months or Longer	1,497
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(3)
Unrealized Loss Position, Total	238,501
Unrealized Loss Position, Accumulated Loss, Total	(696)
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	600	1,711
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	(59)
Unrealized Loss Position, Total	600	1,711
Unrealized Loss Position, Accumulated Loss, Total	$ 0	$ (59)