Note 3 - Investment Securities - Gross Unrealized Losses, Investment Securities Portfolio (Details) $ in Thousands	Jun. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Available for sale securities, less than 12 months, number of investment positions	22	39
Held to Maturity securities, less than 12 months, number of investment positions	35	27
Available for sale securities, less than 12 months, fair value	$ 160,425	$ 440,504
Held to Maturity securities, less than 12 months, fair value	54,267	45,166
Available for sale securities, less than 12 months, unrealized loss	(1,362)	(8,946)
Held to Maturity securities, less than 12 months, unrealized loss	$ (1,071)	$ (1,274)
Available for sale securities, 12 months or longer, number of investment positions	370	394
Held to Maturity securities, 12 months or longer, number of investment positions	166	165
Available for sale securities, 12 months or longer, fair value	$ 2,904,991	$ 3,047,766
Held to Maturity securities, 12 months or longer, fair value	754,754	739,440
Available for sale securities, 12 months or longer, unrealized loss	(279,578)	(262,561)
Held to Maturity securities, 12 months or longer, unrealized loss	$ (42,751)	$ (27,709)
Available for sale securities, total, number of investment positions	392	433
Held to Maturity securities, total, number of investment positions	201	192
Available for sale securities, total, fair value	$ 3,065,416	$ 3,488,270
Held to Maturity securities, total, fair value	809,021	784,606
Available for sale securities, total, unrealized loss	(280,940)	(271,507)
Held to Maturity securities, total, unrealized loss	$ (43,822)	$ (28,983)
Agency Residential MBS [Member]
Available for sale securities, less than 12 months, number of investment positions	1	1
Held to Maturity securities, less than 12 months, number of investment positions	0	1
Available for sale securities, less than 12 months, fair value	$ 498	$ 115
Held to Maturity securities, less than 12 months, fair value	0	0
Available for sale securities, less than 12 months, unrealized loss	(8)	(2)
Held to Maturity securities, less than 12 months, unrealized loss	$ 0	$ 0
Available for sale securities, 12 months or longer, number of investment positions	105	107
Held to Maturity securities, 12 months or longer, number of investment positions	80	93
Available for sale securities, 12 months or longer, fair value	$ 213,122	$ 238,642
Held to Maturity securities, 12 months or longer, fair value	61,517	72,376
Available for sale securities, 12 months or longer, unrealized loss	(20,417)	(18,700)
Held to Maturity securities, 12 months or longer, unrealized loss	$ (5,219)	$ (5,270)
Available for sale securities, total, number of investment positions	106	108
Held to Maturity securities, total, number of investment positions	80	94
Available for sale securities, total, fair value	$ 213,620	$ 238,757
Held to Maturity securities, total, fair value	61,517	72,376
Available for sale securities, total, unrealized loss	(20,425)	(18,702)
Held to Maturity securities, total, unrealized loss	$ (5,219)	$ (5,270)
US States and Political Subdivisions Debt Securities [Member]
Available for sale securities, less than 12 months, number of investment positions	4	2
Held to Maturity securities, less than 12 months, number of investment positions	31	23
Available for sale securities, less than 12 months, fair value	$ 4,698	$ 2,280
Held to Maturity securities, less than 12 months, fair value	17,928	18,599
Available for sale securities, less than 12 months, unrealized loss	(51)	(15)
Held to Maturity securities, less than 12 months, unrealized loss	$ (164)	$ (90)
Available for sale securities, 12 months or longer, number of investment positions	51	50
Held to Maturity securities, 12 months or longer, number of investment positions	38	26
Available for sale securities, 12 months or longer, fair value	$ 57,076	$ 57,614
Held to Maturity securities, 12 months or longer, fair value	35,328	25,466
Available for sale securities, 12 months or longer, unrealized loss	(2,387)	(1,423)
Held to Maturity securities, 12 months or longer, unrealized loss	$ (638)	$ (245)
Available for sale securities, total, number of investment positions	55	52
Held to Maturity securities, total, number of investment positions	69	49
Available for sale securities, total, fair value	$ 61,774	$ 59,894
Held to Maturity securities, total, fair value	53,256	44,065
Available for sale securities, total, unrealized loss	(2,438)	(1,438)
Held to Maturity securities, total, unrealized loss	$ (802)	$ (335)
US Government Agencies Debt Securities [Member]
Available for sale securities, less than 12 months, number of investment positions	2	2
Available for sale securities, less than 12 months, fair value	$ 6,842	$ 9,746
Available for sale securities, less than 12 months, unrealized loss	$ (89)	$ (15)
Available for sale securities, 12 months or longer, number of investment positions	21	19
Available for sale securities, 12 months or longer, fair value	$ 284,364	$ 278,265
Available for sale securities, 12 months or longer, unrealized loss	$ (18,690)	$ (13,836)
Available for sale securities, total, number of investment positions	23	21
Available for sale securities, total, fair value	$ 291,206	$ 288,011
Available for sale securities, total, unrealized loss	$ (18,779)	$ (13,851)
Corporate Debt Securities [Member]
Available for sale securities, less than 12 months, number of investment positions	0	0
Held to Maturity securities, less than 12 months, number of investment positions	4	3
Available for sale securities, less than 12 months, fair value	$ 0	$ 0
Held to Maturity securities, less than 12 months, fair value	36,339	26,567
Available for sale securities, less than 12 months, unrealized loss	0	0
Held to Maturity securities, less than 12 months, unrealized loss	$ (907)	$ (1,184)
Available for sale securities, 12 months or longer, number of investment positions	144	151
Held to Maturity securities, 12 months or longer, number of investment positions	48	46
Available for sale securities, 12 months or longer, fair value	$ 1,843,918	$ 1,894,602
Held to Maturity securities, 12 months or longer, fair value	657,909	641,598
Available for sale securities, 12 months or longer, unrealized loss	(229,129)	(220,035)
Held to Maturity securities, 12 months or longer, unrealized loss	$ (36,894)	$ (22,194)
Available for sale securities, total, number of investment positions	144	151
Held to Maturity securities, total, number of investment positions	52	49
Available for sale securities, total, fair value	$ 1,843,918	$ 1,894,602
Held to Maturity securities, total, fair value	694,248	668,165
Available for sale securities, total, unrealized loss	(229,129)	(220,035)
Held to Maturity securities, total, unrealized loss	$ (37,801)	$ (23,378)
Collateralized Debt Obligations [Member]
Available for sale securities, less than 12 months, number of investment positions	14	34
Available for sale securities, less than 12 months, fair value	$ 143,567	$ 428,363
Available for sale securities, less than 12 months, unrealized loss	$ (1,214)	$ (8,914)
Available for sale securities, 12 months or longer, number of investment positions	49	67
Available for sale securities, 12 months or longer, fair value	$ 506,511	$ 578,643
Available for sale securities, 12 months or longer, unrealized loss	$ (8,955)	$ (8,567)
Available for sale securities, total, number of investment positions	63	101
Available for sale securities, total, fair value	$ 650,078	$ 1,007,006
Available for sale securities, total, unrealized loss	$ (10,169)	$ (17,481)
US Treasury Securities [Member]
Available for sale securities, less than 12 months, number of investment positions	1
Available for sale securities, less than 12 months, fair value	$ 4,820
Available for sale securities, less than 12 months, unrealized loss	$ 0
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 loss	$ 0
Available for sale securities, total, number of investment positions	1
Available for sale securities, total, fair value	$ 4,820
Available for sale securities, total, unrealized loss	$ 0