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Note 1 - Significant Accounting Policies - Fair Value of the Company's Investments by Type (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Amortized Cost	$ 8,111	$ 28,211
Accrued Interest	2	25
Gross Unrealized Gains	1	6
Gross Unrealized Losses	0	(3)
Estimated Fair Value	8,114	28,239
US Government Agencies Debt Securities [Member]
Amortized Cost	7,174	24,986
Accrued Interest	0	14
Gross Unrealized Gains	1	3
Gross Unrealized Losses	0	(3)
Estimated Fair Value	7,175	25,000
Certificates of Deposit [Member]
Amortized Cost	937	3,225
Accrued Interest	2	11
Gross Unrealized Gains	0	3
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 939	$ 3,239

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