Note 10 - Fair Value Measurements - Financial Assets and Liabilities, Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Total Fair Value	$ 481,990	$ 466,439
Assets, fair value	531,568	510,372
Fair Value, Inputs, Level 1 [Member]
Assets, fair value	97,392	59,395
Fair Value, Inputs, Level 2 [Member]
Assets, fair value	433,527	449,266
Fair Value, Inputs, Level 3 [Member]
Assets, fair value	649	1,711
Money Market Funds [Member]
Total Fair Value	47,814	15,462
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	47,814	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	124,043	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	124,043	130,467
Certificates of Deposit [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
Corporate Debt Securities [Member]
Total Fair Value	183,695	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	183,695	292,586
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Total Fair Value	0	0
Commercial Paper [Member]
Total Fair Value	11,376	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	11,376	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	114,413	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	114,413	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	649	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	649	1,711
Mutual Fund [Member]
Total Fair Value	49,578	43,933
Mutual Fund [Member] | Fair Value, Inputs, Level 1 [Member]
Total Fair Value	49,578	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