Note 11 - Regulatory Capital Ratios (Details Textual) - USD ($) $ in Millions		3 Months Ended	6 Months Ended
		Dec. 31, 2016	Sep. 30, 2017	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
Self-imposed Internal Minimum Capital Level		8.00%
Scenario, Forecast [Member]
Capital Conservation Buffer Level R Ratio				2.50%

[1] Under prompt corrective action