Fair Value Measurements, Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Financial assets
Available-for-sale Securities	$ 3,491,679	$ 2,742,025
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	3,900,483	3,960,451
Investment securities held to maturity, fair value	3,145,898	3,401,018
Equity securities with readily determinable fair values, Fair Value	7,000	6,000
Equity Securities without Readily Determinable Fair Value, Amount	29,236	19,225
Equity Securities, FV-NI and without Readily Determinable Fair Value	35,937	25,216
FHLB and Federal Reserve Bank stocks	268,698	295,496
Residential loans held for sale	54,790	20,383
Mortgage servicing rights, net	89,131	77,351	$ 57,158
Financial liabilities
Short-term funding	451,644	605,937
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	3,733,041	4,319,861
Standby letters of credit(c)
Financial liabilities
Standby letters of credit, fair value	3,000	3,000
Lending Related Commitments By Type [Domain]	246,954	270,692
Fair Value, Inputs, Level 1
Financial assets
Cash and due from banks	388,694	436,952
Interest-bearing deposits in other financial institutions	323,130	156,693
Federal funds sold and securities purchased under agreements to resell	965	27,810
Available-for-sale Securities	109,024	109,378
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	999	999
Investment securities held to maturity, fair value	948	936
Equity securities with readily determinable fair value, Carrying Amount	6,701	5,991
Equity securities with readily determinable fair values, Fair Value	6,701	5,991
Fair Value, Inputs, Level 2
Financial assets
Available-for-sale Securities	3,382,655	2,632,647
Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss	3,899,416	3,959,399
Investment securities held to maturity, fair value	3,144,883	3,400,028
Bank owned life insurance, fair value	679,775	676,530
Financial liabilities
Brokered CDs and other time deposits	6,066,937	1,930,158
Brokered CDs and other time deposits, fair value	6,066,937	1,930,158
Short-term funding	451,644	605,937
Short-term funding, fair value	451,624	605,205
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	3,733,041	4,319,861
Advances, Fair Value Disclosure	3,734,775	4,322,264
Other long-term funding	529,459	248,071
Long-term funding, fair value	519,337	242,151
Standby letters of credit	2,691	2,881
Standby letters of credit, fair value	2,691	2,881
Fair Value, Inputs, Level 2 | Other Assets [Member]
Financial assets
Derivative Asset	147,160	67,603
Derivatives (trading and other assets), fair value	147,160	67,603
Fair Value, Inputs, Level 2 | Other Liabilities [Member]
Financial liabilities
Derivatives (trading liabilities)	317,109	254,033
Derivatives (trading and other liabilities), fair value	317,109	254,033
Fair Value, Inputs, Level 3
Financial assets
Equity Securities without Readily Determinable Fair Value, Amount	19,236	19,225
Equity Securities, FV-NI and without Readily Determinable Fair Value	19,236	19,225
Loans, net	29,847,392	28,486,849
Loans, net, fair value	28,705,298	27,481,426
Servicing Asset	89,131	77,351
Mortgage servicing rights, net	89,131	77,351
Financial liabilities
Noninterest-bearing demand, savings, interest-bearing demand, and money market accounts	26,056,389	27,705,996
Noninterest-bearing demand, savings, interest-bearing demand, and money market deposits, fair value	26,056,389	27,705,996
Derivatives (trading liabilities)	0	46
Derivatives (trading and other liabilities), fair value	0	46
Fair Value, Inputs, Level 3 | Mortgage banking(a)(b)
Financial assets
Derivative Asset	407	86
Fair Value, Inputs, Level 3 | Forward commitments (mortgage)
Financial assets
Derivative Asset	806	0
Fair Value, Inputs, NAV
Financial assets
Equity Securities without Readily Determinable Fair Value, Amount	10,000	0
Equity Securities, FV-NI and without Readily Determinable Fair Value	$ 10,000	$ 0