Note 4 - Securities - Available for Sale Securities With Gross Unrealized Losses and Their Fair Value (Details) $ in Thousands	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	2	2
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 26,648	$ 28,654
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	2,948	1,187
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value		28,654
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		1,187
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	26,648
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 2,948	$ 0
Securities have been in a continuous unrealized loss position, number of positions	106	69
Securities have been in a continuous unrealized loss position, fair value	$ 630,554	$ 519,702
Securities have been in a continuous unrealized loss position, unrealized losses	29,914	12,583
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	256,175	325,020
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	5,623	2,827
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	374,379	194,682
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 24,291	$ 9,756
US States and Political Subdivisions Debt Securities [Member]
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	1	1
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 19,427	$ 20,844
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	2,211	1,024
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value		20,844
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		1,024
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	19,427	0
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 2,211	$ 0
Securities have been in a continuous unrealized loss position, number of positions	11
Securities have been in a continuous unrealized loss position, fair value	$ 28,686
Securities have been in a continuous unrealized loss position, unrealized losses	61
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	28,686
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	61
Securities have been in a continuous unrealized loss position, 12 months or more, fair value
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses
Other Debt Obligations [Member]
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	1	1
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 19,427	$ 20,844
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	2,211	1,024
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value		20,844
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		1,024
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	19,427
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 2,211
Securities have been in a continuous unrealized loss position, number of positions	25	14
Securities have been in a continuous unrealized loss position, fair value	$ 128,442	$ 102,767
Securities have been in a continuous unrealized loss position, unrealized losses	10,304	7,233
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	28,686	9,723
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	61	277
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	99,756	93,044
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 10,243	$ 6,956
FNMA [Member]
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	1	1
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 7,221	$ 7,810
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	737	163
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value		7,810
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		163
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	7,221
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 737
Securities have been in a continuous unrealized loss position, number of positions	23	17
Securities have been in a continuous unrealized loss position, fair value	$ 123,654	$ 120,510
Securities have been in a continuous unrealized loss position, unrealized losses	5,276	1,054
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	38,461	109,258
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	904	850
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	85,193	11,252
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 4,372	$ 204
Collateralized Mortgage Backed Securities [Member]
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	1	1
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 7,221	$ 7,810
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	737	163
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value		7,810
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		163
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	7,221
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 737
Securities have been in a continuous unrealized loss position, number of positions	81	55
Securities have been in a continuous unrealized loss position, fair value	$ 502,112	$ 416,935
Securities have been in a continuous unrealized loss position, unrealized losses	19,610	5,350
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	227,489	315,297
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	5,562	2,550
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	274,623	101,638
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 14,048	$ 2,800
Corporate Debt Securities [Member]
Securities have been in a continuous unrealized loss position, number of positions	14	14
Securities have been in a continuous unrealized loss position, fair value	$ 99,756	$ 102,767
Securities have been in a continuous unrealized loss position, unrealized losses	10,243	7,233
Securities have been in a continuous unrealized loss position, less than 12 months, fair value		9,723
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		277
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	99,756	93,044
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 10,243	$ 6,956
REMIC and CMO [Member]
Securities have been in a continuous unrealized loss position, number of positions	56	36
Securities have been in a continuous unrealized loss position, fair value	$ 337,184	$ 249,596
Securities have been in a continuous unrealized loss position, unrealized losses	12,370	3,961
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	189,028	162,781
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	4,658	1,406
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	148,156	86,815
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 7,712	$ 2,555
FHLMC [Member]
Securities have been in a continuous unrealized loss position, number of positions	2	2
Securities have been in a continuous unrealized loss position, fair value	$ 41,274	$ 46,829
Securities have been in a continuous unrealized loss position, unrealized losses	1,964	335
Securities have been in a continuous unrealized loss position, less than 12 months, fair value		43,258
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		294
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	41,274	3,571
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 1,964	$ 41