Note 3 - Investment Securities - Gross Unrealized Losses, Investment Securities Portfolio (Details) $ in Thousands	Sep. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Available for sale securities, less than 12 months, number of investment positions	410	88
Available for sale securities, less than 12 months, fair value	$ 2,957,727	$ 911,513
Available for sale securities, less than 12 months, unrealized losses	$ (316,172)	$ (10,215)
Available for sale securities, 12 months or longer, number of investment positions	57	13
Available for sale securities, 12 months or longer, fair value	$ 476,393	$ 52,358
Available for sale securities, 12 months or longer, unrealized losses	$ (98,313)	$ (200)
Available for sale securities, total, number of investment positions	467	101
Available for sale securities, total, fair value	$ 3,434,120	$ 963,871
Available for sale securities, total, unrealized losses	$ (414,485)	$ (10,415)
Held to Maturity securities, less than 12 months, number of investment positions	241	1
Held to Maturity securities, less than 12 months, fair value	$ 842,105	$ 542
Held to Maturity securities, less than 12 months, unrecognized losses	$ (57,766)	$ (19)
Held to Maturity securities, 12 months or longer, number of investment positions	3	3
Held to Maturity securities, 12 months or longer, fair value	$ 710	$ 530
Held to Maturity securities, 12 months or longer, unrecognized losses	$ (95)	$ (18)
Held to Maturity securities, total, number of investment positions	244	4
Held to Maturity securities, total, fair value	$ 842,815	$ 1,072
Held to Maturity securities, total, unrecognized losses	$ (57,861)	$ (37)
Agency Residential MBS [Member]
Available for sale securities, less than 12 months, number of investment positions	114	7
Available for sale securities, less than 12 months, fair value	$ 295,984	$ 8,900
Available for sale securities, less than 12 months, unrealized losses	$ (29,890)	$ (37)
Available for sale securities, 12 months or longer, number of investment positions	2	2
Available for sale securities, 12 months or longer, fair value	$ 39	$ 47
Available for sale securities, 12 months or longer, unrealized losses	$ (1)	$ 0
Available for sale securities, total, number of investment positions	116	9
Available for sale securities, total, fair value	$ 296,023	$ 8,947
Available for sale securities, total, unrealized losses	$ (29,891)	$ (37)
Held to Maturity securities, less than 12 months, number of investment positions	93	1
Held to Maturity securities, less than 12 months, fair value	$ 102,485	$ 542
Held to Maturity securities, less than 12 months, unrecognized losses	$ (8,183)	$ (19)
Held to Maturity securities, 12 months or longer, number of investment positions	3	3
Held to Maturity securities, 12 months or longer, fair value	$ 710	$ 530
Held to Maturity securities, 12 months or longer, unrecognized losses	$ (95)	$ (18)
Held to Maturity securities, total, number of investment positions	96	4
Held to Maturity securities, total, fair value	$ 103,195	$ 1,072
Held to Maturity securities, total, unrecognized losses	$ (8,278)	$ (37)
US Government-sponsored Enterprises Debt Securities [Member]
Available for sale securities, less than 12 months, number of investment positions	19
Available for sale securities, less than 12 months, fair value	$ 272,525
Available for sale securities, less than 12 months, unrealized losses	$ (16,580)
Available for sale securities, 12 months or longer, number of investment positions	0
Available for sale securities, 12 months or longer, fair value	$ 0
Available for sale securities, 12 months or longer, unrealized losses	$ 0
Available for sale securities, total, number of investment positions	19
Available for sale securities, total, fair value	$ 272,525
Available for sale securities, total, unrealized losses	$ (16,580)
US States and Political Subdivisions Debt Securities [Member]
Available for sale securities, less than 12 months, number of investment positions	63	6
Available for sale securities, less than 12 months, fair value	$ 66,998	$ 2,859
Available for sale securities, less than 12 months, unrealized losses	$ (4,148)	$ (27)
Available for sale securities, 12 months or longer, number of investment positions	3	2
Available for sale securities, 12 months or longer, fair value	$ 1,309	$ 669
Available for sale securities, 12 months or longer, unrealized losses	$ (93)	$ (2)
Available for sale securities, total, number of investment positions	66	8
Available for sale securities, total, fair value	$ 68,307	$ 3,528
Available for sale securities, total, unrealized losses	$ (4,241)	$ (29)
Held to Maturity securities, less than 12 months, number of investment positions	99
Held to Maturity securities, less than 12 months, fair value	$ 82,394
Held to Maturity securities, less than 12 months, unrecognized losses	$ (1,654)
Held to Maturity securities, 12 months or longer, number of investment positions	0
Held to Maturity securities, 12 months or longer, fair value	$ 0
Held to Maturity securities, 12 months or longer, unrecognized losses	$ 0
Held to Maturity securities, total, number of investment positions	99
Held to Maturity securities, total, fair value	$ 82,394
Held to Maturity securities, total, unrecognized losses	$ (1,654)
US Government Agencies Debt Securities [Member]
Available for sale securities, less than 12 months, number of investment positions		0
Available for sale securities, less than 12 months, fair value		$ 0
Available for sale securities, less than 12 months, unrealized losses		$ 0
Available for sale securities, 12 months or longer, number of investment positions		1
Available for sale securities, 12 months or longer, fair value		$ 119
Available for sale securities, 12 months or longer, unrealized losses		$ 0
Available for sale securities, total, number of investment positions		1
Available for sale securities, total, fair value		$ 119
Available for sale securities, total, unrealized losses		$ 0
Debt Security, Corporate, US [Member]
Available for sale securities, less than 12 months, number of investment positions	156	56
Available for sale securities, less than 12 months, fair value	$ 1,787,045	$ 691,555
Available for sale securities, less than 12 months, unrealized losses	$ (256,786)	$ (9,630)
Available for sale securities, 12 months or longer, number of investment positions	36	0
Available for sale securities, 12 months or longer, fair value	$ 323,597	$ 0
Available for sale securities, 12 months or longer, unrealized losses	$ (97,382)	$ 0
Available for sale securities, total, number of investment positions	192	56
Available for sale securities, total, fair value	$ 2,110,642	$ 691,555
Available for sale securities, total, unrealized losses	$ (354,168)	$ (9,630)
Held to Maturity securities, less than 12 months, number of investment positions	49
Held to Maturity securities, less than 12 months, fair value	$ 657,226
Held to Maturity securities, less than 12 months, unrecognized losses	$ (47,929)
Held to Maturity securities, 12 months or longer, number of investment positions	0
Held to Maturity securities, 12 months or longer, fair value	$ 0
Held to Maturity securities, 12 months or longer, unrecognized losses	$ 0
Held to Maturity securities, total, number of investment positions	49
Held to Maturity securities, total, fair value	$ 657,226
Held to Maturity securities, total, unrecognized losses	$ (47,929)
Collateralized Loan Obligations [Member]
Available for sale securities, less than 12 months, number of investment positions	58	19
Available for sale securities, less than 12 months, fair value	$ 535,175	$ 208,199
Available for sale securities, less than 12 months, unrealized losses	$ (8,768)	$ (521)
Available for sale securities, 12 months or longer, number of investment positions	16	8
Available for sale securities, 12 months or longer, fair value	$ 151,448	$ 51,523
Available for sale securities, 12 months or longer, unrealized losses	$ (837)	$ (198)
Available for sale securities, total, number of investment positions	74	27
Available for sale securities, total, fair value	$ 686,623	$ 259,722
Available for sale securities, total, unrealized losses	$ (9,605)	$ (719)