Note 12 - Pension and Other Postretirement Benefit Plans - Employee Benefit Trust (EBT) Shares (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Shares owned by Employee Benefit Trust, beginning balance (in shares)	675,436	800,950
Shares purchased (in shares)	18,391	22,102
Shares released and allocated (in shares)	(142,065)	(147,616)
Shares owned by Employee Benefit Trust, ending balance (in shares)	551,762	675,436
Market value of unallocated shares.	$ 16,216,285	$ 14,616,435