Note 6 - Investment Securities - Investment Securities With Unrealized Losses Not Recognized In Income (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Less than 12 Months Fair Value	$ 177,605	$ 341,755
Less than 12 Months Unrealized Losses	1,107	7,036
12 Months or More Fair Value	129,577	13,429
12 Months or More Unrealized Losses	3,003	656
Total Fair Value	307,182	355,184
Total Unrealized Losses	4,110	7,692
US Government-sponsored Enterprises Debt Securities [Member]
Less than 12 Months Fair Value	42,246	51,657
Less than 12 Months Unrealized Losses	191	460
12 Months or More Fair Value	11,570	0
12 Months or More Unrealized Losses	146	0
Total Fair Value	53,816	51,657
Total Unrealized Losses	337	460
US States and Political Subdivisions Debt Securities [Member]
Less than 12 Months Fair Value	26,809	91,728
Less than 12 Months Unrealized Losses	162	2,526
12 Months or More Fair Value	32,799	1,999
12 Months or More Unrealized Losses	675	10
Total Fair Value	59,608	93,727
Total Unrealized Losses	837	2,536
Residential Mortgage Backed Securities [Member]
Less than 12 Months Fair Value	93,192	154,397
Less than 12 Months Unrealized Losses	642	2,485
12 Months or More Fair Value	55,308	5,841
12 Months or More Unrealized Losses	1,177	202
Total Fair Value	148,500	160,238
Total Unrealized Losses	1,819	2,687
Commercial Mortgage Backed Securities [Member]
Less than 12 Months Fair Value	12,366	43,309
Less than 12 Months Unrealized Losses	109	1,557
12 Months or More Fair Value	29,900	0
12 Months or More Unrealized Losses	1,005	0
Total Fair Value	42,266	43,309
Total Unrealized Losses	1,114	1,557
Corporate Debt Securities [Member]
Less than 12 Months Fair Value	2,992	536
Less than 12 Months Unrealized Losses	3	6
12 Months or More Fair Value	0	5,476
12 Months or More Unrealized Losses	0	435
Total Fair Value	2,992	6,012
Total Unrealized Losses	$ 3	441
Mutual Funds and Equity Securities [Member]
Less than 12 Months Fair Value		128
Less than 12 Months Unrealized Losses		2
12 Months or More Fair Value		113
12 Months or More Unrealized Losses		9
Total Fair Value		241
Total Unrealized Losses		$ 11