Investment Securities - Amortized cost and fair value for held to maturity and available for sale securities (Details) - USD ($) $ in Thousands	Sep. 30, 2026	Dec. 31, 2025
Investment securities held-to-maturity
Amortized Cost	$ 1,905,299	$ 2,048,030
Gross Unrealized Losses	(386,023)	(315,180)
Fair Value	1,519,276	1,732,850
Investment securities available for sale
Amortized Cost	7,111,846	6,696,576
Gross Unrealized Gains	323	39,169
Gross Unrealized Losses	(718,860)	(421,989)
Fair Value	6,393,309	6,313,756
U.S. Government agencies
Investment securities held-to-maturity
Amortized Cost	132,891	132,913
Gross Unrealized Losses	(21,449)	(15,767)
Fair Value	111,442	117,146
Residential mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Investment securities held-to-maturity
Amortized Cost	1,054,751	1,153,024
Gross Unrealized Losses	(219,481)	(177,101)
Fair Value	835,270	975,923
Investment securities available for sale
Amortized Cost	2,063,433	1,826,307
Gross Unrealized Gains	37	10,108
Gross Unrealized Losses	(227,466)	(138,307)
Fair Value	1,836,004	1,698,108
Residential collateralized mortgage-obligations issued by U.S. government agencies or sponsored enterprises
Investment securities held-to-maturity
Amortized Cost	355,715	379,107
Gross Unrealized Losses	(69,930)	(55,232)
Fair Value	285,785	323,875
Investment securities available for sale
Amortized Cost	2,064,461	2,208,710
Gross Unrealized Gains		23,979
Gross Unrealized Losses	(105,817)	(47,105)
Fair Value	1,958,644	2,185,584
Commercial mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Investment securities held-to-maturity
Amortized Cost	318,780	336,910
Gross Unrealized Losses	(65,771)	(58,332)
Fair Value	253,009	278,578
Investment securities available for sale
Amortized Cost	1,142,156	903,209
Gross Unrealized Gains	126	3,282
Gross Unrealized Losses	(113,763)	(74,042)
Fair Value	1,028,519	832,449
State and municipal obligations
Investment securities available for sale
Amortized Cost	1,275,798	1,141,377
Gross Unrealized Gains	1	1,252
Gross Unrealized Losses	(240,763)	(135,217)
Fair Value	1,035,036	1,007,412
Small Business Administration loan-backed securities
Investment securities held-to-maturity
Amortized Cost	43,162	46,076
Gross Unrealized Losses	(9,392)	(8,748)
Fair Value	33,770	37,328
Investment securities available for sale
Amortized Cost	542,998	593,973
Gross Unrealized Gains	159	548
Gross Unrealized Losses	(30,055)	(26,088)
Fair Value	513,102	568,433
Corporate securities
Investment securities available for sale
Amortized Cost	23,000	23,000
Gross Unrealized Losses	(996)	(1,230)
Fair Value	$ 22,004	$ 21,770

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

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