Note 3 - Investments and Fair Value of Financial Instruments (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Impairment of Marketable Securities	$ 0	$ 0
Fair Value, Level 1, 2 and 3 Transfers, Amount	0	0
Assets, Fair Value Disclosure, Total	57,973	23,675
Fair Value, Nonrecurring [Member]
Liabilities, Fair Value Disclosure, Total	0	0	$ 0
Assets, Fair Value Disclosure, Total	$ 0	$ 0	$ 0