Note 2 - Fair Value of Financial Instruments - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Cash and cash equivalents	$ 193,902	$ 137,328
Cash and cash equivalents	193,902	137,328
Cash and cash equivalents, unrealized loss	0
Short-term marketable securities, amortization cost	193,308	268,027
Unrealized gains, short-term securities	4	103
Short-term marketable securities, unrealized loss	(1,934)	(170)
Short-term marketable securities	191,378	267,960
Long-term marketable securities, amortization cost	72,806	111,374
Unrealized gains, long-term securities	0	178
Long-term marketable securities, unrealized loss	(1,809)	(354)
Long-term marketable securities	70,997	111,198
Cash and cash equivalents and marketable securities, amortization cost	460,016	516,729
Unrealized gains, securities	4	281
Unrealized loss, securities	(3,743)	(524)
Cash and cash equivalents and short-term and long-term Marketable Securities, fair value	456,277	516,486
Corporate Debt Securities [Member]
Short-term marketable securities, amortization cost	33,249	28,869
Unrealized gains, short-term securities	4	101
Short-term marketable securities, unrealized loss	(352)	(7)
Short-term marketable securities	32,901	28,963
Long-term marketable securities, amortization cost	35,440	57,762
Unrealized gains, long-term securities	0	160
Long-term marketable securities, unrealized loss	(1,122)	(182)
Long-term marketable securities	34,318	57,740
US Government Agencies Debt Securities [Member]
Short-term marketable securities, amortization cost	159,056	217,160
Unrealized gains, short-term securities	0	2
Short-term marketable securities, unrealized loss	(1,576)	(163)
Short-term marketable securities	157,480	216,999
Long-term marketable securities, amortization cost	17,977	37,664
Unrealized gains, long-term securities	0	0
Long-term marketable securities, unrealized loss	(499)	(136)
Long-term marketable securities	17,478	37,528
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Short-term marketable securities, amortization cost		18,046
Unrealized gains, short-term securities		0
Short-term marketable securities, unrealized loss		0
Short-term marketable securities		18,046
Foreign Government Agencies [Member]
Long-term marketable securities, amortization cost	1,003	1,007
Unrealized gains, long-term securities	0	12
Long-term marketable securities, unrealized loss	(6)	0
Long-term marketable securities	997	1,019
Asset-Backed Securities [Member]
Short-term marketable securities, amortization cost	19,389	3,952
Unrealized gains, short-term securities	0	0
Short-term marketable securities, unrealized loss	(188)	0
Short-term marketable securities	19,201	3,952
Long-term marketable securities, amortization cost		14,941
Unrealized gains, long-term securities		6
Long-term marketable securities, unrealized loss		(36)
Long-term marketable securities		14,911
Cash [Member]
Cash and cash equivalents	46,591	61,220
Cash and cash equivalents	46,591
Money Market Funds [Member]
Cash and cash equivalents	147,311	75,258
Cash and cash equivalents	$ 147,311
Commercial Paper [Member]
Cash and cash equivalents		$ 850