Investment Securities - Amortized cost and fair value for available for sale securities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Investment securities held-to-maturity
Amortized cost	$ 2,301,307	$ 2,487,440
Gross Unrealized Losses	(337,561)	(402,704)
Fair Value	1,963,746	2,084,736
Investment securities available for sale
Amortized cost	5,204,198	5,561,006
Gross Unrealized Gains	3,206	1,898
Gross Unrealized Losses	(643,041)	(778,516)
Fair Value	4,564,363	4,784,388
U.S. Treasuries
Investment securities available for sale
Amortized cost	2,684	74,720
Gross Unrealized Gains	1
Gross Unrealized Losses		(830)
Fair Value	2,685	73,890
U.S. Government agencies
Investment securities held-to-maturity
Amortized cost	147,271	197,267
Gross Unrealized Losses	(19,271)	(24,607)
Fair Value	128,000	172,660
Investment securities available for sale
Amortized cost	191,177	246,089
Gross Unrealized Losses	(15,453)	(21,383)
Fair Value	175,724	224,706
Residential mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Investment securities held-to-maturity
Amortized cost	1,333,263	1,438,102
Gross Unrealized Losses	(188,925)	(227,312)
Fair Value	1,144,338	1,210,790
Investment securities available for sale
Amortized cost	1,702,457	1,822,104
Gross Unrealized Gains	491	294
Gross Unrealized Losses	(216,862)	(264,092)
Fair Value	1,486,086	1,558,306
Residential collateralized mortgage-obligations issued by U.S. government agencies or sponsored enterprises
Investment securities held-to-maturity
Amortized cost	419,838	444,883
Gross Unrealized Losses	(58,371)	(68,139)
Fair Value	361,467	376,744
Investment securities available for sale
Amortized cost	574,447	626,735
Gross Unrealized Gains	49
Gross Unrealized Losses	(82,254)	(99,313)
Fair Value	492,242	527,422
Commercial mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Investment securities held-to-maturity
Amortized cost	349,860	354,055
Gross Unrealized Losses	(61,691)	(71,327)
Fair Value	288,169	282,728
Investment securities available for sale
Amortized cost	1,215,415	1,217,125
Gross Unrealized Gains	2,545	1,516
Gross Unrealized Losses	(157,131)	(194,471)
Fair Value	1,060,829	1,024,170
State and municipal obligations
Investment securities available for sale
Amortized cost	1,123,634	1,129,750
Gross Unrealized Gains	63	2
Gross Unrealized Losses	(134,394)	(152,291)
Fair Value	989,303	977,461
Small Business Administration loan-backed securities
Investment securities held-to-maturity
Amortized cost	51,075	53,133
Gross Unrealized Losses	(9,303)	(11,319)
Fair Value	41,772	41,814
Investment securities available for sale
Amortized cost	363,885	413,950
Gross Unrealized Gains	57	86
Gross Unrealized Losses	(34,432)	(42,350)
Fair Value	329,510	371,686
Corporate securities
Investment securities available for sale
Amortized cost	30,499	30,533
Gross Unrealized Losses	(2,515)	(3,786)
Fair Value	$ 27,984	$ 26,747

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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Amortized cost excluding accrued interest, before allowance for credit loss, of 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 excluding accrued interest, before allowance for credit loss, of 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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