Note 6 - Income Taxes - Federal Income Tax Reconciled to the Effective Income Tax Rate (Details)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	21.00%	35.00%
Increase in taxes arising from state income taxes, net of federal income tax benefit	2.00%	3.00%	3.00%
Per diem and other non-deductible expenses	1.00%	2.00%	4.00%
Decrease in federal deferred taxes due to decrease in statutory rate	0.00%	0.00%	(100.00%)
Federal tax credits	(2.00%)	(2.00%)	(1.00%)
Other, net	(1.00%)	(1.00%)	(1.00%)
Effective tax rate	21.00%	23.00%	(60.00%)

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

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the income tax rates.

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Percentage of the difference, between reported income tax expense (benefit) and the expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, that is attributable to tax exempt income, equity in earnings (loss) of an unconsolidated subsidiary, minority interest income (expense), tax holiday, disposition of a business, disposition of an asset, repatriation of foreign earnings, repatriation of foreign earnings jobs creation act of 2004, change in enacted tax rate, prior year income taxes, change in deferred tax asset valuation allowance, and other adjustments.

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