Note 9 - Pension and Other Postretirement Benefit Plans - Components of Net Expense for Pension, Outside, and Other Postretirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Employee Pension Plan [Member]
Interest cost	$ 216	$ 226
Amortization of unrecognized loss	174	201
Expected return on plan assets	(348)	(348)
Net expense	42	79
Directors' Plan [Member]
Interest cost	23	24
Amortization of unrecognized loss	(23)	(21)
Net expense	20	24
Service cost	10	11
Amortization of past service liability	10	10
Other Postretirement Benefit Plans [Member]
Interest cost	76	80
Amortization of unrecognized loss		12
Net expense	134	161
Service cost	79	90
Amortization of past service liability	$ (21)	$ (21)