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Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Investment securities held to maturity:
Amortized Cost	$ 2,668,068	$ 0
Gross Unrealized Gains	0
Gross Unrealized Losses	(29,997)
Fair Value	2,638,071
Investment securities available for sale:
Amortized Cost	7,571,447	11,091,254
Gross Unrealized Gains	7,172	31,540
Gross Unrealized Losses	(534,938)	(1,334,132)
Fair Value	7,043,681	9,788,662
Accrued interest receivable on investment securities held to maturity	5,900
Discount included in amortized cost of investment securities HTM	(687,900)
Accrued interest receivable on investment securities available for sale	$ 27,700	$ 26,600
Debt securities, available-for-sale, accrued interest, after allowance for credit loss, noncurrent, statement of financial position [extensible enumeration]	Other assets	Other assets
U.S. Treasury securities
Investment securities available for sale:
Amortized Cost	$ 1,177,006	$ 588,082
Gross Unrealized Gains	1,456	9,547
Gross Unrealized Losses	(4,167)	0
Fair Value	1,174,295	597,629
U.S. Government agency securities
Investment securities available for sale:
Amortized Cost	29,993	29,993
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,150)	(1,053)
Fair Value	28,843	28,940
Mortgage-backed securities issued by U.S. Government agencies
Investment securities available for sale:
Amortized Cost	1,518,224	1,021,612
Gross Unrealized Gains	1,311	2,037
Gross Unrealized Losses	(119,043)	(97,985)
Fair Value	1,400,492	925,664
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Investment securities held to maturity:
Amortized Cost	2,668,068
Gross Unrealized Gains	0
Gross Unrealized Losses	(29,997)
Fair Value	2,638,071
Investment securities available for sale:
Amortized Cost	2,272,694	7,523,399
Gross Unrealized Gains	287	1,192
Gross Unrealized Losses	(256,936)	(1,094,212)
Fair Value	2,016,045	6,430,379
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Investment securities available for sale:
Amortized Cost	659,706	692,487
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(111,709)	(104,892)
Fair Value	547,997	587,595
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Investment securities available for sale:
Amortized Cost	1,904,765	1,226,672
Gross Unrealized Gains	4,118	18,764
Gross Unrealized Losses	(41,757)	(35,653)
Fair Value	1,867,126	1,209,783
Corporate debt securities and other debt securities
Investment securities available for sale:
Amortized Cost	9,059	9,009
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(176)	(337)
Fair Value	$ 8,883	$ 8,672

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