Note 3 - Investment Securities - Amortized Cost, Unrealized Gains and Losses, and Estimated Fair Value of Investment Securities Portfolio (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Debt securities available for sale, amortized cost	$ 3,979,429	$ 4,269,948
Debt securities available for sale, gross unrealized gains	829	1,360
Debt securities available for sale, gross unrealized losses	(280,940)	(271,507)
Debt securities available for sale	3,699,318	3,999,801
Debt securities held to maturity, amortized cost	860,869	878,397
Debt securities held to maturity, gross unrecognized gains	24	148
Debt securities held to maturity, gross unrecognized losses	(43,822)	(28,983)
Debt securities held to maturity, fair value	817,071	849,562
Debt securities, amortized cost	4,840,298	5,148,345
Debt securities, gross unrecognized gains	853	1,508
Debt securities, gross unrecognized losses	(324,762)	(300,490)
Total	4,516,389	4,849,363
Agency Residential MBS [Member]
Debt securities available for sale, amortized cost	243,230	258,150
Debt securities available for sale, gross unrealized gains	1	6
Debt securities available for sale, gross unrealized losses	(20,425)	(18,702)
Debt securities available for sale	222,806	239,454
Debt securities held to maturity, amortized cost	67,777	78,565
Debt securities held to maturity, gross unrecognized gains	17	17
Debt securities held to maturity, gross unrecognized losses	(5,219)	(5,270)
Debt securities held to maturity, fair value	62,575	73,312
US Government Agencies Debt Securities [Member]
Debt securities available for sale, amortized cost	309,985	308,768
Debt securities available for sale, gross unrealized gains	0	2
Debt securities available for sale, gross unrealized losses	(18,779)	(13,851)
Debt securities available for sale	291,206	294,919
US States and Political Subdivisions Debt Securities [Member]
Debt securities available for sale, amortized cost	72,192	72,679
Debt securities available for sale, gross unrealized gains	4	42
Debt securities available for sale, gross unrealized losses	(2,438)	(1,438)
Debt securities available for sale	69,758	71,283
Debt securities held to maturity, amortized cost	61,043	71,182
Debt securities held to maturity, gross unrecognized gains	7	47
Debt securities held to maturity, gross unrecognized losses	(802)	(335)
Debt securities held to maturity, fair value	60,248	70,894
Corporate Debt Securities [Member]
Debt securities available for sale, amortized cost	2,084,391	2,129,103
Debt securities available for sale, gross unrealized gains	356	480
Debt securities available for sale, gross unrealized losses	(229,129)	(220,035)
Debt securities available for sale	1,855,618	1,909,548
Debt securities held to maturity, amortized cost	732,049	728,650
Debt securities held to maturity, gross unrecognized gains	0	84
Debt securities held to maturity, gross unrecognized losses	(37,801)	(23,378)
Debt securities held to maturity, fair value	694,248	705,356
Collateralized Debt Obligations [Member]
Debt securities available for sale, amortized cost	1,264,811	1,501,248
Debt securities available for sale, gross unrealized gains	468	830
Debt securities available for sale, gross unrealized losses	(10,169)	(17,481)
Debt securities available for sale	1,255,110	$ 1,484,597
US Treasury Securities [Member]
Debt securities available for sale, amortized cost	4,820
Debt securities available for sale, gross unrealized gains	0
Debt securities available for sale, gross unrealized losses	0
Debt securities available for sale	$ 4,820

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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Amount of investment in debt security measured at amortized cost (held-to-maturity) and amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), before allowance for credit losses.

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Amount, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Represents the amount of gross unrecognized gains of debt securities, available-for-sale and held-to-maturity.

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No definition available.

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No definition available.

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