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Investment Securities - Amortized cost and fair value for available for sale securities (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Investment securities held-to-maturity
Amortized cost	$ 2,096,727	$ 2,254,670
Gross Unrealized Losses	(331,240)	(420,143)
Fair Value	1,765,487	1,834,527
Investment securities available for sale
Amortized cost	6,468,315	5,129,216
Gross Unrealized Gains	30,641	701
Gross Unrealized Losses	(456,156)	(809,324)
Fair Value	6,042,800	4,320,593
U.S. Treasuries
Investment securities available for sale
Amortized cost		10,654
Gross Unrealized Gains		2
Fair Value		10,656
U.S. Government agencies
Investment securities held-to-maturity
Amortized cost	132,911	147,272
Gross Unrealized Losses	(16,729)	(23,498)
Fair Value	116,182	123,774
Investment securities available for sale
Amortized cost		169,207
Gross Unrealized Losses		(18,789)
Fair Value		150,418
Residential mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Investment securities held-to-maturity
Amortized cost	1,187,818	1,297,543
Gross Unrealized Losses	(186,684)	(241,204)
Fair Value	1,001,134	1,056,339
Investment securities available for sale
Amortized cost	1,689,961	1,659,851
Gross Unrealized Gains	7,641	97
Gross Unrealized Losses	(147,237)	(282,423)
Fair Value	1,550,365	1,377,525
Residential collateralized mortgage-obligations issued by U.S. government agencies or sponsored enterprises
Investment securities held-to-maturity
Amortized cost	386,777	411,721
Gross Unrealized Losses	(58,177)	(72,057)
Fair Value	328,600	339,664
Investment securities available for sale
Amortized cost	2,268,056	557,288
Gross Unrealized Gains	18,908	19
Gross Unrealized Losses	(49,790)	(98,212)
Fair Value	2,237,174	459,095
Commercial mortgage-backed securities issued by U.S. government agencies or sponsored enterprises
Investment securities held-to-maturity
Amortized cost	342,054	348,338
Gross Unrealized Losses	(60,516)	(72,391)
Fair Value	281,538	275,947
Investment securities available for sale
Amortized cost	749,857	1,234,573
Gross Unrealized Gains	2,809	562
Gross Unrealized Losses	(77,054)	(194,580)
Fair Value	675,612	1,040,555
State and municipal obligations
Investment securities available for sale
Amortized cost	1,112,505	1,117,330
Gross Unrealized Gains	754	2
Gross Unrealized Losses	(152,147)	(171,609)
Fair Value	961,112	945,723
Small Business Administration loan-backed securities
Investment securities held-to-maturity
Amortized cost	47,167	49,796
Gross Unrealized Losses	(9,134)	(10,993)
Fair Value	38,033	38,803
Investment securities available for sale
Amortized cost	619,437	351,814
Gross Unrealized Gains	528	19
Gross Unrealized Losses	(28,405)	(41,721)
Fair Value	591,560	310,112
Corporate securities
Investment securities available for sale
Amortized cost	28,499	28,499
Gross Unrealized Gains	1
Gross Unrealized Losses	(1,523)	(1,990)
Fair Value	$ 26,977	$ 26,509

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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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