Note 3 - Cash, Cash Equivalents, Investments and Restricted Cash - Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Continuous Unrealized Loss Position, Less than 12 Months	$ 118,391	$ 73,930
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(114)	(975)
Continuous Unrealized Loss Position, 12 Months or Longer	71,373	211,083
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,527)	(7,247)
Unrealized Loss Position, Total	189,764	285,013
Unrealized Loss Position, Accumulated Loss, Total	(1,641)	(8,222)
Corporate Debt Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months	20,792	72,943
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(19)	(973)
Continuous Unrealized Loss Position, 12 Months or Longer	70,806	202,074
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,520)	(6,988)
Unrealized Loss Position, Total	91,598	275,017
Unrealized Loss Position, Accumulated Loss, Total	(1,539)	(7,961)
US Treasury and Government Short-Term Debt Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months	97,599
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(95)
Continuous Unrealized Loss Position, 12 Months or Longer	0
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Unrealized Loss Position, Total	97,599
Unrealized Loss Position, Accumulated Loss, Total	(95)
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	567	1,711
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(7)	(59)
Unrealized Loss Position, Total	567	1,711
Unrealized Loss Position, Accumulated Loss, Total	$ (7)	$ (59)