Note 4 - Fair Value Measurements - Financial Assets and Liabilities, Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Total Fair Value	$ 466,439	$ 552,546
Assets, fair value	510,372	584,332
Fair Value, Inputs, Level 1 [Member]
Assets, fair value	59,395	46,114
Fair Value, Inputs, Level 2 [Member]
Assets, fair value	449,266	535,817
Fair Value, Inputs, Level 3 [Member]
Assets, fair value	1,711	2,401
Money Market Funds [Member]
Total Fair Value	15,462	14,328
Money Market Funds [Member] \| Fair Value, Inputs, Level 1 [Member]
Total Fair Value	15,462	14,328
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	130,467	141,478
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	130,467	141,478
Certificates of Deposit [Member] \| Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
Corporate Debt Securities [Member]
Total Fair Value	292,586	386,883
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	292,586	386,883
Corporate Debt Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
Commercial Paper [Member]
Total Fair Value	17,928
Commercial Paper [Member] \| Fair Value, Inputs, Level 1 [Member]
Total Fair Value	0
Commercial Paper [Member] \| Fair Value, Inputs, Level 2 [Member]
Total Fair Value	17,928
Commercial Paper [Member] \| Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0
US Government Agencies Short-Term Debt Securities [Member]
Total Fair Value	8,285	7,456
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	8,285	7,456
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	1,711	2,401
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	1,711	2,401
Mutual Fund [Member]
Total Fair Value	43,933	31,786
Mutual Fund [Member] \| Fair Value, Inputs, Level 1 [Member]
Total Fair Value	43,933	31,786
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