Note 12 - Regulatory Matters (Details Textual) - USD ($) $ / shares in Units, $ in Millions									3 Months Ended		9 Months Ended		44 Months Ended
	Dec. 19, 2018	Oct. 11, 2018	Sep. 19, 2018	Jul. 12, 2018	Jun. 20, 2018	Apr. 12, 2018	Mar. 21, 2018	Jan. 11, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Jan. 01, 2019	Dec. 31, 2017	Apr. 19, 2016	Jan. 30, 2015	Dec. 31, 2009
Preferred Securities of Subsidiary Trust									$ 44.0		$ 44.0		$ 44.0		$ 43.4
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
Trust Preferred Securities Included in Tier One Capital									$ 44.0		$ 44.0		$ 44.0		$ 43.4
Capital Conservation Buffer									2.50%		2.50%		2.50%
Common Stock, Dividends, Per Share, Declared				$ 0.24		$ 0.22		$ 0.22
Common Stock, Dividends, Per Share, Cash Paid			$ 0.24		$ 0.22		$ 0.22		$ 0.24	$ 0.19	$ 0.68	$ 0.55
Dividends, Basis Points Reduction of Risk-based Capital Ratio, Pro Forma Basis											0.40%
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
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared		$ 0.25
Subsequent Event [Member] | Special Dividend [Member]
Common Stock, Dividends, Per Share, Declared		$ 0.75
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	$ 0.25
Scenario, Forecast [Member] | Special Dividend [Member]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.75