Note 10 - Pension and Other Postretirement Benefit Plans - Components of Net Expense for Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Employee Pension Plan [Member]
Employee Pension Plan:
Interest cost	$ 226	$ 221	$ 678	$ 663
Amortization of unrecognized (gain) loss	201	291	604	872
Expected return on plan assets	(348)	(350)	(1,044)	(1,050)
Net expense	79	162	238	485
Directors Plan [Member]
Employee Pension Plan:
Interest cost	24	24	72	72
Amortization of unrecognized (gain) loss	(21)	(14)	(65)	(42)
Net expense	23	31	70	93
Service cost	11	11	33	33
Amortization of past service liability (credit)	9	10	30	30
Other Postretirement Benefit Plan [Member]
Employee Pension Plan:
Interest cost	80	75	240	225
Amortization of unrecognized (gain) loss	12	30	36	90
Net expense	160	179	482	536
Service cost	90	95	270	285
Amortization of past service liability (credit)	$ (22)	$ (21)	$ (64)	$ (64)