Note 16 - Assets and Liabilities Measured and Reported at Fair Value - Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Securities available-for-sale, fair value	$ 571,522	$ 570,074
Fair Value, Measurements, Recurring [Member]
Securities available-for-sale, fair value	571,522	570,074
Interest rate swaps	182	203
Total assets	571,704	570,277
Interest rate swaps	148	178
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale, fair value	516	75,697
Interest rate swaps
Total assets	516	75,697
Interest rate swaps
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale, fair value	571,006	494,377
Interest rate swaps	182	203
Total assets	571,188	494,580
Interest rate swaps	148	178
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale, fair value
Interest rate swaps
Total assets	0	0
Interest rate swaps
US Government-sponsored Enterprises Debt Securities [Member]
Securities available-for-sale, fair value	372,664	268,090
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available-for-sale, fair value	372,664	268,090
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale, fair value
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale, fair value	372,664	268,090
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale, fair value
US Treasury and Government [Member] | Fair Value, Measurements, Recurring [Member]
Securities available-for-sale, fair value		74,998
US Treasury and Government [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale, fair value		74,998
US Treasury and Government [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale, fair value
US Treasury and Government [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale, fair value
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available-for-sale, fair value	146,720	168,843
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Measurements, Recurring [Member]
Securities available-for-sale, fair value	146,720	168,843
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale, fair value
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale, fair value	146,720	168,843
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale, fair value
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale, fair value	51,622	57,444
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available-for-sale, fair value	51,622	57,444
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale, fair value
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale, fair value	51,622	57,444
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale, fair value
Common Stock [Member]
Securities available-for-sale, fair value	516	699
Common Stock [Member] | Fair Value, Measurements, Recurring [Member]
Securities available-for-sale, fair value	516	699
Common Stock [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale, fair value	516	699
Common Stock [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale, fair value
Common Stock [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale, fair value