Securities - Amortized cost and fair value for available for sale securities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Investment securities held-to-maturity
Amortized cost	$ 2,487,440	$ 2,683,241
Gross Unrealized Losses	(402,704)	(433,073)
Fair Value	2,084,736	2,250,168
Investment securities available for sale
Amortized cost	5,561,006	6,216,141
Gross Unrealized Gains	1,898	4,054
Gross Unrealized Losses	(778,516)	(893,373)
Fair Value	4,784,388	5,326,822
Gross realized gains	1,335	103	$ 750
Gross realized losses	(1,292)	(73)	(648)
Securities gains, net	43	30	$ 102
U.S. Treasuries
Investment securities available for sale
Amortized cost	74,720	272,416
Gross Unrealized Losses	(830)	(6,778)
Fair Value	73,890	265,638
U.S. Government agencies
Investment securities held-to-maturity
Amortized cost	197,267	197,262
Gross Unrealized Losses	(24,607)	(29,787)
Fair Value	172,660	167,475
Investment securities available for sale
Amortized cost	246,089	245,972
Gross Unrealized Losses	(21,383)	(26,884)
Fair Value	224,706	219,088
Residential mortgage pass-through securities issued or guaranteed by U.S. government agencies or sponsored enterprises
Investment securities held-to-maturity
Amortized cost	1,438,102	1,591,646
Gross Unrealized Losses	(227,312)	(255,093)
Fair Value	1,210,790	1,336,553
Investment securities available for sale
Amortized cost	1,822,104	1,996,405
Gross Unrealized Gains	294
Gross Unrealized Losses	(264,092)	(298,052)
Fair Value	1,558,306	1,698,353
Residential collateralized mortgage-obligations issued by U.S. government agencies or sponsored enterprises
Investment securities held-to-maturity
Amortized cost	444,883	474,660
Gross Unrealized Losses	(68,139)	(69,664)
Fair Value	376,744	404,996
Investment securities available for sale
Amortized cost	626,735	708,337
Gross Unrealized Losses	(99,313)	(107,292)
Fair Value	527,422	601,045
Commercial mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Investment securities held-to-maturity
Amortized cost	354,055	362,586
Gross Unrealized Losses	(71,327)	(66,304)
Fair Value	282,728	296,282
Investment securities available for sale
Amortized cost	1,217,125	1,196,700
Gross Unrealized Gains	1,516	2,542
Gross Unrealized Losses	(194,471)	(198,844)
Fair Value	1,024,170	1,000,398
State and municipal obligations
Investment securities available for sale
Amortized cost	1,129,750	1,269,525
Gross Unrealized Gains	2	1,210
Gross Unrealized Losses	(152,291)	(205,883)
Fair Value	977,461	1,064,852
Small Business Administration loan-backed securities
Investment securities held-to-maturity
Amortized cost	53,133	57,087
Gross Unrealized Losses	(11,319)	(12,225)
Fair Value	41,814	44,862
Investment securities available for sale
Amortized cost	413,950	491,203
Gross Unrealized Gains	86	302
Gross Unrealized Losses	(42,350)	(46,695)
Fair Value	371,686	444,810
Corporate securities.
Investment securities available for sale
Amortized cost	30,533	35,583
Gross Unrealized Losses	(3,786)	(2,945)
Fair Value	$ 26,747	$ 32,638

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 of realized gain (loss) on investment in debt and equity securities.

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