Note 12 - Other Comprehensive Income (Loss) (Details Textual) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Other Comprehensive Income (Loss), Remeasurement of Deferred Tax Assets and Liabilities	$ 506
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%		35.00%
Stockholders' Equity Attributable to Parent, Ending Balance		$ 366,500	$ 333,644		$ 313,872	$ 286,519
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Stockholders' Equity Attributable to Parent, Ending Balance		(5,330)	(1,781)	[1]	(1,211)	965
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Previously Reported [Member]
Stockholders' Equity Attributable to Parent, Ending Balance			(2,278)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Stockholders' Equity Attributable to Parent, Ending Balance		408	193	[1]	(16)	(60)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Previously Reported [Member]
Stockholders' Equity Attributable to Parent, Ending Balance			234
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Stockholders' Equity Attributable to Parent, Ending Balance		$ (220)	(342)	[1]	$ (272)	$ (273)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] | Previously Reported [Member]
Stockholders' Equity Attributable to Parent, Ending Balance			$ (392)

[1] December 31, 2017 AOCI component balances reflect a correction of incorrectly reported year-end balances in Note 12 of the 2017 Form 10-K, which were presented as $(2,278), $234, and $(392) for securities available for sale, cash flow hedges, and minimum pension liability, respectively.