Note 12 - Pension and Other Postretirement Benefit Plans - Benefit Payments Under Postretirement Plan Reflect Expected Future Service to be Paid (Details) - Other Postretirement Benefits Plan [Member] $ in Thousands	Dec. 31, 2017 USD ($)
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	$ 236
2019	251
2020	256
2021	270
2022	294
2023 – 2027	$ 1,561

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

Dec. 31, 2017

USD ($)

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

$ 236

251

256

270

294

$ 1,561