Fair Value of Assets and Liabilities - Schedule of The Balances Of Assets And Liabilities Measured At Fair Value On A Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Assets
Securities available for sale:	$ 3,860,264	$ 3,825,569
Derivative asset	51,036	55,048
Liabilities
Derivative liability	72,251	74,719
Government-sponsored residential mortgage-backed securities
Assets
Securities available for sale:	2,594,507	2,533,309
Government-sponsored commercial mortgage-backed securities
Assets
Securities available for sale:	1,039,854	1,060,331
U.S. Treasury securities
Assets
Securities available for sale:	50,175	50,350
Fair Value, Recurring
Assets
Investments for employee retirement benefits	102,324	106,534
Deferred compensation investments	2,203	2,384
Loans held for sale	25,814	22,761
Mortgage servicing rights	39,842	40,709
Total	4,082,237	4,053,463
Liabilities
Total	72,342	74,819
Fair Value, Recurring \| Risk participation agreements
Assets
Derivative asset	9	10
Liabilities
Derivative liability	8	7
Fair Value, Recurring \| Matched customer book
Assets
Derivative asset	978	434
Liabilities
Derivative liability	877	330
Fair Value, Recurring \| Foreign currency loan
Assets
Derivative asset	9	13
Liabilities
Derivative liability	1
Fair Value, Recurring \| Mortgage derivatives
Assets
Derivative asset	754	458
Liabilities
Derivative liability	91	100
Fair Value, Recurring \| Designated as Hedging Instrument \| Interest rate swaps
Assets
Derivative asset	91	30
Liabilities
Derivative liability		24
Fair Value, Recurring \| Not Designated as Hedging Instrument \| Interest rate swaps
Assets
Derivative asset	49,949	54,561
Liabilities
Derivative liability	71,365	74,358
Fair Value, Recurring \| Government-sponsored residential mortgage-backed securities
Assets
Securities available for sale:	2,594,507	2,533,309
Fair Value, Recurring \| Government-sponsored commercial mortgage-backed securities
Assets
Securities available for sale:	1,039,854	1,060,331
Fair Value, Recurring \| U.S. Treasury securities
Assets
Securities available for sale:	50,175	50,350
Fair Value, Recurring \| State and municipal bonds and obligations
Assets
Securities available for sale:	175,728	181,579
Fair Value, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Investments for employee retirement benefits	86,848	94,736
Deferred compensation investments	2,203	2,384
Loans held for sale	0	0
Mortgage servicing rights	0	0
Total	139,226	147,470
Liabilities
Total	0	0
Fair Value, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Risk participation agreements
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Fair Value, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Matched customer book
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Fair Value, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Foreign currency loan
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0
Fair Value, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Mortgage derivatives
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Fair Value, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Designated as Hedging Instrument \| Interest rate swaps
Assets
Derivative asset	0	0
Liabilities
Derivative liability		0
Fair Value, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Not Designated as Hedging Instrument \| Interest rate swaps
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Fair Value, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Government-sponsored residential mortgage-backed securities
Assets
Securities available for sale:	0	0
Fair Value, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Government-sponsored commercial mortgage-backed securities
Assets
Securities available for sale:	0	0
Fair Value, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| U.S. Treasury securities
Assets
Securities available for sale:	50,175	50,350
Fair Value, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| State and municipal bonds and obligations
Assets
Securities available for sale:	0	0
Fair Value, Recurring \| Significant Other Observable Inputs (Level 2)
Assets
Investments for employee retirement benefits	15,476	11,798
Deferred compensation investments	0	0
Loans held for sale	25,814	22,761
Mortgage servicing rights	0	0
Total	3,903,169	3,865,284
Liabilities
Total	72,342	74,819
Fair Value, Recurring \| Significant Other Observable Inputs (Level 2) \| Risk participation agreements
Assets
Derivative asset	9	10
Liabilities
Derivative liability	8	7
Fair Value, Recurring \| Significant Other Observable Inputs (Level 2) \| Matched customer book
Assets
Derivative asset	978	434
Liabilities
Derivative liability	877	330
Fair Value, Recurring \| Significant Other Observable Inputs (Level 2) \| Foreign currency loan
Assets
Derivative asset	9	13
Liabilities
Derivative liability	1
Fair Value, Recurring \| Significant Other Observable Inputs (Level 2) \| Mortgage derivatives
Assets
Derivative asset	754	458
Liabilities
Derivative liability	91	100
Fair Value, Recurring \| Significant Other Observable Inputs (Level 2) \| Designated as Hedging Instrument \| Interest rate swaps
Assets
Derivative asset	91	30
Liabilities
Derivative liability		24
Fair Value, Recurring \| Significant Other Observable Inputs (Level 2) \| Not Designated as Hedging Instrument \| Interest rate swaps
Assets
Derivative asset	49,949	54,561
Liabilities
Derivative liability	71,365	74,358
Fair Value, Recurring \| Significant Other Observable Inputs (Level 2) \| Government-sponsored residential mortgage-backed securities
Assets
Securities available for sale:	2,594,507	2,533,309
Fair Value, Recurring \| Significant Other Observable Inputs (Level 2) \| Government-sponsored commercial mortgage-backed securities
Assets
Securities available for sale:	1,039,854	1,060,331
Fair Value, Recurring \| Significant Other Observable Inputs (Level 2) \| U.S. Treasury securities
Assets
Securities available for sale:	0	0
Fair Value, Recurring \| Significant Other Observable Inputs (Level 2) \| State and municipal bonds and obligations
Assets
Securities available for sale:	175,728	181,579
Fair Value, Recurring \| Significant Unobservable Inputs (Level 3)
Assets
Investments for employee retirement benefits	0	0
Deferred compensation investments	0	0
Loans held for sale	0	0
Mortgage servicing rights	39,842	40,709
Total	39,842	40,709
Liabilities
Total	0	0
Fair Value, Recurring \| Significant Unobservable Inputs (Level 3) \| Risk participation agreements
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Fair Value, Recurring \| Significant Unobservable Inputs (Level 3) \| Matched customer book
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Fair Value, Recurring \| Significant Unobservable Inputs (Level 3) \| Foreign currency loan
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0
Fair Value, Recurring \| Significant Unobservable Inputs (Level 3) \| Mortgage derivatives
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Fair Value, Recurring \| Significant Unobservable Inputs (Level 3) \| Designated as Hedging Instrument \| Interest rate swaps
Assets
Derivative asset	0	0
Liabilities
Derivative liability		0
Fair Value, Recurring \| Significant Unobservable Inputs (Level 3) \| Not Designated as Hedging Instrument \| Interest rate swaps
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Fair Value, Recurring \| Significant Unobservable Inputs (Level 3) \| Government-sponsored residential mortgage-backed securities
Assets
Securities available for sale:	0	0
Fair Value, Recurring \| Significant Unobservable Inputs (Level 3) \| Government-sponsored commercial mortgage-backed securities
Assets
Securities available for sale:	0	0
Fair Value, Recurring \| Significant Unobservable Inputs (Level 3) \| U.S. Treasury securities
Assets
Securities available for sale:	0	0
Fair Value, Recurring \| Significant Unobservable Inputs (Level 3) \| State and municipal bonds and obligations
Assets
Securities available for sale:	$ 0	$ 0

Fair value portion of asset recognized for present right to economic benefit.

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The total amount of cash and securities held by third party trustees pursuant to terms of debt instruments or other agreements as of the date of each statement of financial position presented, which can be used by the trustee only to pay the noncurrent portion of specified obligations.

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