Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	$ 3,491,679	$ 2,742,025
Equity securities with readily determinable fair values, Fair Value	7,000	6,000
Mortgage servicing rights, net	89,131	77,351	$ 57,158
Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	109,024	109,378
Equity securities with readily determinable fair values, Fair Value	6,701	5,991
Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	3,382,655	2,632,647
Fair Value, Inputs, Level 3
Assets, Fair Value Disclosure [Abstract]
Mortgage servicing rights, net	89,131	77,351
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	0	46
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Designated as Hedging Instrument
Assets, Fair Value Disclosure [Abstract]
Interest Rate Fair Value Hedge Asset at Fair Value	2,109	4,349
Foreign Currency Contract, Asset, Fair Value Disclosure	2,886	416
Liabilities, Fair Value Disclosure [Abstract]
Interest Rate Fair Value Hedge Liability at Fair Value	21,520	1,260
Foreign Currency Contracts, Liability, Fair Value Disclosure	134	972
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Assets, Fair Value Disclosure [Abstract]
Trading assets	806	0
Mortgage servicing rights, net	89,131	77,351
Interest rate-related instruments — customer and mirror | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Designated as Hedging Instrument
Assets, Fair Value Disclosure [Abstract]
Trading assets	2,109	4,349
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	21,520	1,260
Interest rate-related instruments — customer and mirror | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Not Designated as Hedging Instrument [Member]
Assets, Fair Value Disclosure [Abstract]
Trading assets	140,414	62,401
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	294,062	251,398
Foreign Exchange Forward [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Trading assets	1,751	437
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	1,393	402
Foreign Exchange Forward [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Designated as Hedging Instrument
Assets, Fair Value Disclosure [Abstract]
Trading assets	2,886	416
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	134	972
Forward Commitments to Sell Residential Mortgage Loans | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities		46
Forward Commitments to Sell Residential Mortgage Loans | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Not Designated as Hedging Instrument [Member]
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	0
US Treasury Securities
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	109,024	109,378
US Treasury Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	109,024	109,378
Agency Securities
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	13,590	13,532
Agency Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	13,590	13,532
US States and Political Subdivisions Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	210,317	230,714
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	210,317	230,714
Residential Related Securities | FNMA/FHLMC
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	1,436,759	1,604,610
Residential Related Securities | FNMA/FHLMC | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	1,436,759	1,604,610
Residential Related Securities | Government National Mortgage Association (GNMA) [Member]
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	1,384,670	497,596
Residential Related Securities | Government National Mortgage Association (GNMA) [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	1,384,670	497,596
Commercial mortgage-related securities | FNMA/FHLMC
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	16,154	17,142
Commercial mortgage-related securities | FNMA/FHLMC | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	16,154	17,142
Commercial mortgage-related securities | Government National Mortgage Association (GNMA) [Member]
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	176,474	110,462
Commercial mortgage-related securities | Government National Mortgage Association (GNMA) [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	176,474	110,462
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	138,514	151,191
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	138,514	151,191
US Government-sponsored Enterprises Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	3,261	4,477
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	3,261	4,477
Other Debt securities
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	2,915	2,922
Other Debt securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	2,915	2,922
Available-for-sale Securities [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	109,024	109,378
Available-for-sale Securities [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
AFS investment securities, at fair value	3,382,655	2,632,647
Other Debt And Other Equity Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Equity securities with readily determinable fair values, Fair Value	6,701	5,991
Residential loans held for sale | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Trading assets	54,790	20,383
Mortgage banking(a)(b) | Fair Value, Inputs, Level 3
Assets, Fair Value Disclosure [Abstract]
Trading assets	407	86
Mortgage banking(a)(b) | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Assets, Fair Value Disclosure [Abstract]
Trading assets	407	$ 86
Forward Commitments to Sell Residential Mortgage Loans | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	$ 0