Note 10 - Fair Value Measurements - Financial Assets and Liabilities, Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Total Fair Value	$ 665,577	$ 466,439
Assets, fair value	715,402	510,372
Fair Value, Inputs, Level 1 [Member]
Assets, fair value	93,679	59,395
Fair Value, Inputs, Level 2 [Member]
Assets, fair value	621,123	449,266
Fair Value, Inputs, Level 3 [Member]
Assets, fair value	600	1,711
Money Market Funds [Member]
Total Fair Value	43,854	15,462
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	43,854	15,462
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	0	0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
Certificates of Deposit [Member]
Total Fair Value	123,368	130,467
Certificates of Deposit [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	0	0
Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	123,368	130,467
Certificates of Deposit [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
Corporate Debt Securities [Member]
Total Fair Value	130,614	292,586
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	0	0
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	130,614	292,586
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
Commercial Paper [Member]
Total Fair Value	4,976	17,928
Commercial Paper [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	0	0
Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	4,976	17,928
Commercial Paper [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
US Government Agencies Short-Term Debt Securities [Member]
Total Fair Value	362,165	8,285
US Government Agencies Short-Term Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	0	0
US Government Agencies Short-Term Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	362,165	8,285
US Government Agencies Short-Term Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
Auction Rate Securities [Member]
Total Fair Value	600	1,711
Auction Rate Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	0	0
Auction Rate Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	0	0
Auction Rate Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	600	1,711
Mutual Fund [Member]
Total Fair Value	49,825	43,933
Mutual Fund [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	49,825	43,933
Mutual Fund [Member] | Fair Value, Inputs, Level 2 [Member]
Total Fair Value	0	0
Mutual Fund [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	$ 0	$ 0