Note 3 - Investment Securities - Investment Securities With Unrealized Losses Not Recognized In Income (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Less than 12 Months Fair Value	$ 145,433	$ 341,755
Less than 12 Months Unrealized Losses	1,039	7,036
12 Months or More Fair Value	193,588	13,429
12 Months or More Unrealized Losses	4,655	656
Total Fair Value	339,021	355,184
Total Unrealized Losses	5,694	7,692
US Government-sponsored Enterprises Debt Securities [Member]
Less than 12 Months Fair Value	11,544	51,657
Less than 12 Months Unrealized Losses	43	460
12 Months or More Fair Value	25,298	0
12 Months or More Unrealized Losses	394	0
Total Fair Value	36,842	51,657
Total Unrealized Losses	437	460
US States and Political Subdivisions Debt Securities [Member]
Less than 12 Months Fair Value	40,402	91,728
Less than 12 Months Unrealized Losses	413	2,526
12 Months or More Fair Value	33,965	1,999
12 Months or More Unrealized Losses	860	10
Total Fair Value	74,367	93,727
Total Unrealized Losses	1,273	2,536
Residential Mortgage Backed Securities [Member]
Less than 12 Months Fair Value	77,312	154,397
Less than 12 Months Unrealized Losses	481	2,485
12 Months or More Fair Value	99,986	5,841
12 Months or More Unrealized Losses	2,254	202
Total Fair Value	177,298	160,238
Total Unrealized Losses	2,735	2,687
Commercial Mortgage Backed Securities [Member]
Less than 12 Months Fair Value	7,758	43,309
Less than 12 Months Unrealized Losses	62	1,557
12 Months or More Fair Value	34,139	0
12 Months or More Unrealized Losses	1,146	0
Total Fair Value	41,897	43,309
Total Unrealized Losses	1,208	1,557
Asset-backed Securities [Member]
Less than 12 Months Fair Value	1,166
Less than 12 Months Unrealized Losses	4
12 Months or More Fair Value
12 Months or More Unrealized Losses
Total Fair Value	1,166
Total Unrealized Losses	4
Corporate Debt Securities [Member]
Less than 12 Months Fair Value	7,251	536
Less than 12 Months Unrealized Losses	36	6
12 Months or More Fair Value	200	5,476
12 Months or More Unrealized Losses	1	435
Total Fair Value	7,451	6,012
Total Unrealized Losses	$ 37	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