Note 6 - Investment Securities - Securities in a Continuous Unrealized Loss Position (Details) - USD ($)	Sep. 30, 2022	Dec. 31, 2021
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value	$ 494,386,000	$ 708,711,000
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses	84,386,000	10,159,000
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value	494,781,000	155,915,000
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses	119,803,000	4,514,000
Available for sale securities in a continuous unrealized loss position, fair value	989,167,000	864,626,000
Available for sale securities in a continuous unrealized loss position, unrealized losses	204,189,000	14,673,000
Held to maturity securities in a continuous unrealized loss position, less than 12 months, fair value	523,307,000	1,082,607,000
Held to maturity securities in a continuous unrealized loss position, less than 12 months, unrealized losses	95,802,000	17,534,000
Held to maturity securities in a continuous unrealized loss position, 12 months or more, fair value	740,257,000	143,750,000
Held to maturity securities in a continuous unrealized loss position, 12 months or more, unrealized losses	199,060,000	3,849,000
Held to maturity securities in a continuous unrealized loss position, fair value	1,263,564,000	1,226,357,000
Held to maturity securities in a continuous unrealized loss position, unrealized losses	294,862,000	21,383,000
US Government Agencies Debt Securities [Member]
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value	0	0
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses	0	0
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value	18,396,000	24,928,000
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses	1,411,000	743,000
Available for sale securities in a continuous unrealized loss position, fair value	18,396,000	24,928,000
Available for sale securities in a continuous unrealized loss position, unrealized losses	1,411,000	743,000
Held to maturity securities in a continuous unrealized loss position, less than 12 months, fair value	48,025,000	0
Held to maturity securities in a continuous unrealized loss position, less than 12 months, unrealized losses	4,764,000	0
Held to maturity securities in a continuous unrealized loss position, 12 months or more, fair value	0	0
Held to maturity securities in a continuous unrealized loss position, 12 months or more, unrealized losses	0	0
Held to maturity securities in a continuous unrealized loss position, fair value	48,025,000	0
Held to maturity securities in a continuous unrealized loss position, unrealized losses	4,764,000	0
Collateralized Mortgage Obligations [Member]
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value	155,546,000	188,416,000
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses	23,587,000	2,982,000
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value	165,469,000	57,708,000
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses	43,417,000	2,028,000
Available for sale securities in a continuous unrealized loss position, fair value	321,015,000	246,124,000
Available for sale securities in a continuous unrealized loss position, unrealized losses	67,004,000	5,010,000
Held to maturity securities in a continuous unrealized loss position, less than 12 months, fair value	125,412,000	183,376,000
Held to maturity securities in a continuous unrealized loss position, less than 12 months, unrealized losses	14,609,000	6,719,000
Held to maturity securities in a continuous unrealized loss position, 12 months or more, fair value	177,469,000	81,994,000
Held to maturity securities in a continuous unrealized loss position, 12 months or more, unrealized losses	52,980,000	2,084,000
Held to maturity securities in a continuous unrealized loss position, fair value	302,881,000	265,370,000
Held to maturity securities in a continuous unrealized loss position, unrealized losses	67,589,000	8,803,000
Agency Mortgage-backed Securities [Member]
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value	193,757,000	365,859,000
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses	39,579,000	4,896,000
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value	221,572,000	39,928,000
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses	54,678,000	615,000
Available for sale securities in a continuous unrealized loss position, fair value	415,329,000	405,787,000
Available for sale securities in a continuous unrealized loss position, unrealized losses	94,257,000	5,511,000
Held to maturity securities in a continuous unrealized loss position, less than 12 months, fair value	349,870,000	899,231,000
Held to maturity securities in a continuous unrealized loss position, less than 12 months, unrealized losses	76,429,000	10,815,000
Held to maturity securities in a continuous unrealized loss position, 12 months or more, fair value	562,788,000	61,756,000
Held to maturity securities in a continuous unrealized loss position, 12 months or more, unrealized losses	146,080,000	1,765,000
Held to maturity securities in a continuous unrealized loss position, fair value	912,658,000	960,987,000
Held to maturity securities in a continuous unrealized loss position, unrealized losses	222,509,000	12,580,000
US States and Political Subdivisions Debt Securities [Member]
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value	44,747,000	0
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses	6,356,000	0
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value	0	0
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses	0	0
Available for sale securities in a continuous unrealized loss position, fair value	44,747,000	0
Available for sale securities in a continuous unrealized loss position, unrealized losses	6,356,000	0
Corporate Debt Securities [Member]
Available for sale securities in a continuous unrealized loss position, less than 12 months, fair value	100,336,000	154,436,000
Available for sale securities in a continuous unrealized loss position, less than 12 months, unrealized losses	14,864,000	2,281,000
Available for sale securities in a continuous unrealized loss position, 12 months or more, fair value	89,344,000	33,351,000
Available for sale securities in a continuous unrealized loss position, 12 months or more, unrealized losses	20,297,000	1,128
Available for sale securities in a continuous unrealized loss position, fair value	189,680,000	187,787,000
Available for sale securities in a continuous unrealized loss position, unrealized losses	$ 35,161,000	$ 3,409,000