Note 4 - Securities - Available for Sale Securities With Gross Unrealized Losses and Their Fair Value (Details)	Jun. 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		$ 589,648,000
Securities have been in a continuous unrealized loss position, unrealized losses		24,131,000
Securities have been in a continuous unrealized loss position, less than 12 months, fair value		143,932,000
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		2,845,000
Securities have been in a continuous unrealized loss position, 12 months or more, fair value		445,716,000
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses		$ 21,286,000
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	52	2
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 429,137,000	$ 27,306,000
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	10,637,000	2,144,000
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value	137,825,000	0
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	1,109,000	0
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	291,312,000	27,306,000
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 9,528,000	$ 2,144,000
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	$ 122,036,000	$ 118,535,000
Securities have been in a continuous unrealized loss position, unrealized losses	7,964,000	11,465,000
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	19,720,000	19,113,000
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	280,000	888,000
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	102,316,000	99,422,000
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 7,684,000	$ 10,577,000
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		$ 4,220,000
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		4,220,000
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		$ 19,940,000
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss		1,557,000
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		19,940,000
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses		$ 1,557,000
Collateralized Loan Obligations [Member]
Securities have been in a continuous unrealized loss position, number of positions	10	11
Securities have been in a continuous unrealized loss position, fair value	$ 80,046,000	$ 86,752,000
Securities have been in a continuous unrealized loss position, unrealized losses	734,000	1,645,000
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	80,046,000	86,752,000
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	734,000	1,645,000
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	0	0
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 0	$ 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		$ 209,507,000
Securities have been in a continuous unrealized loss position, unrealized losses		13,110,000
Securities have been in a continuous unrealized loss position, less than 12 months, fair value		110,085,000
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		2,533,000
Securities have been in a continuous unrealized loss position, 12 months or more, fair value		99,422,000
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses		$ 10,577,000
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	26	1
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 202,082,000	$ 19,940,000
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	8,698,000	1,557,000
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value	99,766,000	0
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	1,014,000	0
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	102,316,000	19,940,000
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 7,684,000	$ 1,557,000
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		$ 85,046,000
Securities have been in a continuous unrealized loss position, unrealized losses		2,448,000
Securities have been in a continuous unrealized loss position, less than 12 months, fair value		6,372,000
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		17,000
Securities have been in a continuous unrealized loss position, 12 months or more, fair value		78,674,000
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses		$ 2,431,000
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	5	1
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 60,396,000	$ 7,366,000
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	572,000	587,000
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value	0	0
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	0	0
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	60,396,000	7,366,000
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 572,000	$ 587,000
REMIC and CMO [Member]
Securities have been in a continuous unrealized loss position, number of positions	19	39
Securities have been in a continuous unrealized loss position, fair value	$ 126,261,000	$ 243,756,000
Securities have been in a continuous unrealized loss position, unrealized losses	1,109,000	7,177,000
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	38,059,000	17,308,000
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	95,000	200,000
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	88,202,000	226,448,000
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 1,014,000	$ 6,977,000
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		$ 380,141,000
Securities have been in a continuous unrealized loss position, unrealized losses		11,021,000
Securities have been in a continuous unrealized loss position, less than 12 months, fair value		33,847,000
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses		312,000
Securities have been in a continuous unrealized loss position, 12 months or more, fair value		346,294,000
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses		$ 10,709,000
Held-to-maturity securities have been in a continuous unrealized loss position, number of positions	26	1
Held-to-maturity securities have been in a continuous unrealized loss position, fair value	$ 227,055,000	$ 7,366,000
Held-to-maturity securities have been in a continuous unrealized loss position, unrealized loss	1,939,000	587,000
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, fair value	38,059,000	0
Held-to-maturity securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	95,000	0
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, fair value	188,996,000	7,366,000
Held-to-maturity securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 1,844,000	$ 587,000
FHLMC [Member]
Securities have been in a continuous unrealized loss position, number of positions	2	3
Securities have been in a continuous unrealized loss position, fair value	$ 40,398,000	$ 51,288,000
Securities have been in a continuous unrealized loss position, unrealized losses	258,000	1,396,000
Securities have been in a continuous unrealized loss position, less than 12 months, fair value	0	10,116,000
Securities have been in a continuous unrealized loss position, less than 12 months, unrealized losses	0	95,000
Securities have been in a continuous unrealized loss position, 12 months or more, fair value	40,398,000	41,172,000
Securities have been in a continuous unrealized loss position, 12 months or more, unrealized losses	$ 258,000	$ 1,301,000
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		$ 51,000
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		51,000
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