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Note 1 - Significant Accounting Policies - Fair Value of the Company's Investments by Type (Details) $ in Thousands	Sep. 30, 2021 USD ($)
Amortized Cost	$ 28,211
Accrued Interest	25
Gross Unrealized Gains	6
Gross Unrealized Losses	(3)
Estimated Fair Value	28,239
US Government Agencies Debt Securities [Member]
Amortized Cost	24,986
Accrued Interest	14
Gross Unrealized Gains	3
Gross Unrealized Losses	(3)
Estimated Fair Value	25,000
Certificates of Deposit [Member]
Amortized Cost	3,225
Accrued Interest	11
Gross Unrealized Gains	3
Gross Unrealized Losses	0
Estimated Fair Value	$ 3,239

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