Note 15 - Regulatory Capital Ratios (Details Textual) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Dec. 31, 2016	Mar. 31, 2018	Jan. 01, 2019	Mar. 31, 2017
Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	[1]		6.50%		6.50%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	[1]		8.00%		8.00%
Capital Required to be Well Capitalized to Risk Weighted Assets	[1]		10.00%		10.00%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	[1]		5.00%		5.00%
Capital Conservation Buffer Level R Ratio			0.625%
Capital Conservation Buffer Phase In Period			4 years
Increase (Decrease) in Capital		$ 3
Scenario, Forecast [Member]
Capital Conservation Buffer Level R Ratio				2.50%

[1] Under prompt corrective action