Note 15 - Assets and Liabilities Measured and Reported at Fair Value - Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Securities available-for-sale, fair value	$ 598,081	$ 574,524
Fair Value, Measurements, Recurring [Member]
Securities available-for-sale, fair value	598,081	574,524
Interest rate swaps	1,987	579
Total assets	600,068	575,103
Interest rate swaps	1,275	259
Liabilities
Interest rate swaps	1,275	259
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale, fair value		149,984
Interest rate swaps
Total assets		149,984
Interest rate swaps
Liabilities
Interest rate swaps
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale, fair value	598,081	424,540
Interest rate swaps	1,987	579
Total assets	600,068	425,119
Interest rate swaps	1,275	259
Liabilities
Interest rate swaps	1,275	259
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
Liabilities
Interest rate swaps
US Government-sponsored Enterprises Debt Securities [Member]
Securities available-for-sale, fair value	402,411	213,844
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available-for-sale, fair value	402,411	213,844
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	402,411	213,844
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		149,984
US Treasury and Government [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale, fair value		149,984
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	151,748	161,507
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Measurements, Recurring [Member]
Securities available-for-sale, fair value	151,748	161,507
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	151,748	161,507
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	43,922	49,189
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available-for-sale, fair value	43,922	49,189
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	43,922	49,189
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