Note 9 - Cash, Cash Equivalents, Investments and Restricted Cash - Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Continuous Unrealized Loss Position, Less than 12 Months	$ 322,693	$ 293,410
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(7,213)	(1,804)
Continuous Unrealized Loss Position, 12 Months or Longer	15,326	7,161
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(205)	(122)
Unrealized Loss Position, Total	338,019	300,571
Unrealized Loss Position, Accumulated Loss, Total	(7,418)	(1,926)
Corporate Debt Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months	315,366	285,954
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(7,045)	(1,765)
Continuous Unrealized Loss Position, 12 Months or Longer	12,950	4,760
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(86)	(3)
Unrealized Loss Position, Total	328,316	290,714
Unrealized Loss Position, Accumulated Loss, Total	(7,131)	(1,768)
US Treasury and Government Short-Term Debt Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months	7,327
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(168)
Continuous Unrealized Loss Position, 12 Months or Longer	0
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Unrealized Loss Position, Total	7,327
Unrealized Loss Position, Accumulated Loss, Total	(168)
US Government Agencies Short-Term Debt Securities [Member]
Continuous Unrealized Loss Position, Less than 12 Months		7,456
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(39)
Continuous Unrealized Loss Position, 12 Months or Longer		0
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Unrealized Loss Position, Total		7,456
Unrealized Loss Position, Accumulated Loss, Total		(39)
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	2,376	2,401
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(119)	(119)
Unrealized Loss Position, Total	2,376	2,401
Unrealized Loss Position, Accumulated Loss, Total	$ (119)	$ (119)