Note 7 - Income Taxes (Details Textual) - USD ($)	3 Months Ended	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2020
Income Tax Expense (Benefit), Total	$ 5,280,000	$ (8,317,000)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest, Total	$ 19,490,000	$ (29,850,000)
Effective Income Tax Rate Reconciliation, Percent, Total	27.00%	28.00%
Marketable Securities, Unrealized Gain (Loss), Total	$ 19,531,000	$ (28,640,000)
Domestic Tax Authority [Member]
Open Tax Year	2016 2017 2018
State and Local Jurisdiction [Member]
Open Tax Year	2015 2016 2017 2018
Forecast [Member]
Effective Income Tax Rate Reconciliation, Percent, Total			19.00%

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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