Note 11 - Regulatory Matters (Details Textual) - USD ($) $ / shares in Units, $ in Millions					9 Months Ended	56 Months Ended
	Oct. 10, 2019	Jul. 11, 2019	Apr. 11, 2019	Jan. 17, 2019	Sep. 30, 2019	Sep. 30, 2019	May 07, 2019	Dec. 31, 2018	Apr. 19, 2016	Jan. 30, 2015	Dec. 31, 2009
Preferred Securities of Subsidiary Trust					$ 44.6	$ 44.6		$ 44.1
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
Capital Conservation Buffer								2.50%
Common Stock, Dividends, Per Share, Declared		$ 0.27	$ 0.26	$ 0.26
Stock Repurchase Program, Authorized Amount							$ 20.0			$ 20.0
Stock Repurchase Program Additional Authorized Amount									$ 15.0
Stock Repurchased During Period, Shares					231,000	1,390,000
Stock Repurchased During Period, Value					$ 7.1	$ 32.6
Treasury Stock Acquired, Average Cost Per Share					$ 30.78	$ 23.47
Dividends Payable, Date to be Paid		Sep. 18, 2019	Jun. 19, 2019	Mar. 20, 2019
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.27
Dividends Payable, Date to be Paid	Dec. 18, 2019