Note 12 - Pension and Other Postretirement Benefit Plans - Benefit Payments Under the Director Plan, Which Reflect Expected Future Service, Expected to be Paid (Details) - Directors' Plan [Member] $ in Thousands	Dec. 31, 2017 USD ($)
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	$ 248
2019	288
2020	288
2021	288
2022	288
2023 – 2027	$ 1,052

Note 12 - Pension and Other Postretirement Benefit Plans - Benefit Payments Under the Director Plan, Which Reflect Expected Future Service, Expected to be Paid (Details) - Directors' Plan [Member]
$ in Thousands

Dec. 31, 2017

USD ($)

Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months

$ 248

288

288

288

288

$ 1,052