Note 4 - Securities - Available for Sale Securities With Gross Unrealized Losses and Their Fair Value (Details) $ in Thousands	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Securities have been in a continuous unrealized loss position, number of positions		87
Securities have been in a continuous unrealized loss position, fair value		$ 589,648
Securities have been in a continuous unrealized loss position, unrealized losses		24,131
Securities have been in a continuous unrealized loss position, less than 12 months, fair value		143,932
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		2,845
Securities have been in a continuous unrealized loss position, 12 months or more, fair value		445,716
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses		$ 21,286
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	61	2
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 473,934	$ 27,306
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	12,043	2,144
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value	226,622	0
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	1,740	0
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	247,312	27,306
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 10,303	$ 2,144
Corporate Debt Securities [Member]
Securities have been in a continuous unrealized loss position, number of positions	16	16
Securities have been in a continuous unrealized loss position, fair value	$ 120,543	$ 118,535
Securities have been in a continuous unrealized loss position, unrealized losses	9,457	11,465
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	9,663	19,113
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	338	888
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	110,880	99,422
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 9,119	$ 10,577
US States and Political Subdivisions Debt Securities [Member]
Securities have been in a continuous unrealized loss position, number of positions		3
Securities have been in a continuous unrealized loss position, fair value		$ 4,220
Securities have been in a continuous unrealized loss position, unrealized losses		0
Securities have been in a continuous unrealized loss position, less than 12 months, fair value		4,220
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		0
Securities have been in a continuous unrealized loss position, 12 months or more, fair value		0
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses		$ 0
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions		1
Held-to-maturity securities have been in a continuous unrealized loss position, fair value		$ 19,940
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss		1,557
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value		0
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		0
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value		19,940
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses		$ 1,557
Collateralized Loan Obligations [Member]
Securities have been in a continuous unrealized loss position, number of positions	12	11
Securities have been in a continuous unrealized loss position, fair value	$ 91,916	$ 86,752
Securities have been in a continuous unrealized loss position, unrealized losses	960	1,645
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	63,821	86,752
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	485	1,645
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	28,095	0
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 475	$ 0
Other Debt Obligations [Member]
Securities have been in a continuous unrealized loss position, number of positions		30
Securities have been in a continuous unrealized loss position, fair value		$ 209,507
Securities have been in a continuous unrealized loss position, unrealized losses		13,110
Securities have been in a continuous unrealized loss position, less than 12 months, fair value		110,085
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		2,533
Securities have been in a continuous unrealized loss position, 12 months or more, fair value		99,422
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses		$ 10,577
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	28	1
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 212,459	$ 19,940
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	10,417	1,557
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value	73,484	0
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	823	0
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	138,975	19,940
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 9,594	$ 1,557
FNMA [Member]
Securities have been in a continuous unrealized loss position, number of positions		14
Securities have been in a continuous unrealized loss position, fair value		$ 85,046
Securities have been in a continuous unrealized loss position, unrealized losses		2,448
Securities have been in a continuous unrealized loss position, less than 12 months, fair value		6,372
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		17
Securities have been in a continuous unrealized loss position, 12 months or more, fair value		78,674
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses		$ 2,431
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	7	1
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 69,075	$ 7,366
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	388	587
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value	14,888	0
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	30	0
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	54,187	7,366
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 358	$ 587
REMIC and CMO [Member]
Securities have been in a continuous unrealized loss position, number of positions	25	39
Securities have been in a continuous unrealized loss position, fair value	$ 157,584	$ 243,756
Securities have been in a continuous unrealized loss position, unrealized losses	1,123	7,177
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	138,250	17,308
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	887	200
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	19,334	226,448
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 236	$ 6,977
Collateralized Mortgage Backed Securities [Member]
Securities have been in a continuous unrealized loss position, number of positions		57
Securities have been in a continuous unrealized loss position, fair value		$ 380,141
Securities have been in a continuous unrealized loss position, unrealized losses		11,021
Securities have been in a continuous unrealized loss position, less than 12 months, fair value		33,847
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		312
Securities have been in a continuous unrealized loss position, 12 months or more, fair value		346,294
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses		$ 10,709
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	33	1
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 261,475	$ 7,366
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	1,626	587
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value	153,138	0
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	917	0
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	108,337	7,366
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 709	$ 587
FHLMC [Member]
Securities have been in a continuous unrealized loss position, number of positions	1	3
Securities have been in a continuous unrealized loss position, fair value	$ 34,816	$ 51,288
Securities have been in a continuous unrealized loss position, unrealized losses	115	1,396
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	0	10,116
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	0	95
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	34,816	41,172
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 115	$ 1,301
GNMA [Member]
Securities have been in a continuous unrealized loss position, number of positions		1
Securities have been in a continuous unrealized loss position, fair value		$ 51
Securities have been in a continuous unrealized loss position, unrealized losses		0
Securities have been in a continuous unrealized loss position, less than 12 months, fair value		51
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		0
Securities have been in a continuous unrealized loss position, 12 months or more, fair value		0
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses		$ 0