Note 6 - Accrued Retirement Benefits (Details Textual) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax	$ 20,800,000	$ 21,800,000
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year	800,000
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	542,000
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	$ 0	$ 0