Note 10 - Income Taxes - The Components of the Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax asset:
Postretirement benefits	$ 7,800	$ 6,798
Allowance for loan losses	9,518	9,437
Stock based compensation	3,525	3,404
Depreciation	2,135	1,941
Unrealized loss on securities available for sale	2,770	395
Derivative financial instruments	1,027	1,724
Adjustment required to recognize funded status of postretirement pension plans	3,246	3,833
Gain on sale of buildings	2,211	2,531
Other	2,434	2,460
Deferred tax asset	34,666	32,523
Deferred tax liability:
Fair value adjustment on financial assets carried at fair value	150	187
Fair value adjustment on financial liabilities carried at fair value	11,943	14,364
Other	4,684	3,411
Deferred tax liability	16,777	17,962
Net deferred tax asset included in other assets	$ 17,889	$ 14,561