Note 12 - Regulatory Matters (Details Textual) - USD ($) $ / shares in Units, $ in Millions									3 Months Ended		9 Months Ended		32 Months Ended
	Dec. 20, 2017	Oct. 12, 2017	Sep. 20, 2017	Jul. 13, 2017	Jun. 21, 2017	Apr. 13, 2017	Mar. 22, 2017	Jan. 12, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Jan. 01, 2019	Dec. 31, 2016	Apr. 19, 2016	Jan. 30, 2015
Preferred Securities of Subsidiary Trust									$ 43.3		$ 43.3		$ 43.3		$ 42.8
Maximum Restricted Core Element Allowed in Tier One Capital Percent											25.00%
Maximum Level of Consolidated Aggregate Assets Allowing for Inclusion of Trust Preferred Securities in Tier One Capital									15,000.0		$ 15,000.0		15,000.0
Trust Preferred Securities Included in Tier One Capital									$ 43.3		$ 43.3		$ 43.3		$ 42.8
Capital Conservation Buffer									2.50%		2.50%		2.50%
Common Stock, Dividends, Per Share, Declared				$ 0.19		$ 0.18		$ 0.18
Stock Repurchase Program, Authorized Amount																	$ 20.0
Stock Repurchase Program Additional Authorized Amount																$ 15.0
Stock Repurchased During Period, Shares											0		956,419
Stock Repurchased During Period, Value													$ 19.5
Treasury Stock Acquired, Average Cost Per Share													$ 20.38
Common Stock, Dividends, Per Share, Cash Paid			$ 0.19		$ 0.18		$ 0.18		$ 0.19	$ 0.17	$ 0.55	$ 0.49
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared		$ 0.19
Scenario, Forecast [Member]
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy to Risk Weighted Assets														7.00%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets														8.50%
Capital Required for Capital Adequacy to Risk Weighted Assets														10.50%
Common Stock, Dividends, Per Share, Cash Paid	$ 0.19