Note 4 - Securities - Available for Sale Securities With Gross Unrealized Losses and Their Fair Value (Details) $ in Thousands	Jun. 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	$ 27,301	$ 28,654
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	2,439	1,187
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value	7,373	28,654
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	590	1,187
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	19,928
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 1,849	$ 0
Securities have been in a continuous unrealized loss position, number of positions	89	69
Securities have been in a continuous unrealized loss position, fair value	$ 586,989	$ 519,702
Securities have been in a continuous unrealized loss position, unrealized losses	25,353	12,583
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	396,621	325,020
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	11,380	2,827
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	190,368	194,682
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 13,973	$ 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	$ 19,928	$ 20,844
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	1,849	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	19,928	0
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 1,849	$ 0
Securities have been in a continuous unrealized loss position, number of positions	2
Securities have been in a continuous unrealized loss position, fair value	$ 5,088
Securities have been in a continuous unrealized loss position, unrealized losses	31
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	5,088
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	31
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	$ 19,928	$ 20,844
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	1,849	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	19,928
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 1,849
Securities have been in a continuous unrealized loss position, number of positions	16	14
Securities have been in a continuous unrealized loss position, fair value	$ 105,620	$ 102,767
Securities have been in a continuous unrealized loss position, unrealized losses	9,499	7,233
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	14,482	9,723
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	637	277
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	91,138	93,044
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 8,862	$ 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	$ 7,373	$ 7,810
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	590	163
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value	7,373	7,810
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	590	163
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	0
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 0
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	$ 126,338	$ 120,510
Securities have been in a continuous unrealized loss position, unrealized losses	4,191	1,054
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	110,983	109,258
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	3,445	850
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	15,355	11,252
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 746	$ 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	$ 7,373	$ 7,810
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	590	163
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value	7,373	7,810
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	590	163
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses
Securities have been in a continuous unrealized loss position, number of positions	73	55
Securities have been in a continuous unrealized loss position, fair value	$ 481,369	$ 416,935
Securities have been in a continuous unrealized loss position, unrealized losses	15,854	5,350
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	382,139	315,297
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	10,743	2,550
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	99,230	101,638
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 5,111	$ 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	$ 100,532	$ 102,767
Securities have been in a continuous unrealized loss position, unrealized losses	9,468	7,233
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	9,394	9,723
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	606	277
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	91,138	93,044
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 8,862	$ 6,956
REMIC and CMO [Member]
Securities have been in a continuous unrealized loss position, number of positions	48	36
Securities have been in a continuous unrealized loss position, fair value	$ 312,201	$ 249,596
Securities have been in a continuous unrealized loss position, unrealized losses	10,093	3,961
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	231,236	162,781
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	5,860	1,406
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	80,965	86,815
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 4,233	$ 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	$ 42,830	$ 46,829
Securities have been in a continuous unrealized loss position, unrealized losses	1,570	335
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	39,920	43,258
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	1,438	294
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	2,910	3,571
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 132	$ 41