Fair Value Accounting (Schedule of Financial Instruments Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Assets
Investment securities available for sale	$ 9,237,191	$ 9,678,103
Mortgage loans held for sale	48,994	51,136
Collateralized mortgage obligations issued by U.S. Government sponsored enterprises
Assets
Investment securities available for sale	578,836	655,127
U.S. Treasury securities
Assets
Investment securities available for sale	509,460	471,813
Mortgage-backed securities issued by U.S. Government agencies
Assets
Investment securities available for sale	892,254	792,749
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Assets
Investment securities available for sale	6,261,752	6,895,070
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Assets
Investment securities available for sale	938,735	805,945
Corporate debt securities and other debt securities
Assets
Investment securities available for sale	8,648	8,601
Level 1
Assets
Trading securities	0	0
Investment securities available for sale	509,460	471,813
Other investments	0	0
Mutual funds and mutual funds held in rabbi trusts	49,119	42,659
Derivative assets	0	0
Liabilities
Securities sold short	2,362	3,370
Mutual funds held in rabbi trusts	34,768	27,944
Derivative liabilities	0	0
Level 2
Assets
Trading securities	13,555	8,295
Investment securities available for sale	8,727,731	9,206,290
Other investments	0	0
Mutual funds and mutual funds held in rabbi trusts	0	0
Derivative assets	161,163	89,815
Liabilities
Securities sold short	0	0
Mutual funds held in rabbi trusts	0	0
Derivative liabilities	387,118	339,227
Level 3
Assets
Trading securities	0	0
Investment securities available for sale	0	0
Other investments	11,789	11,172
Mutual funds and mutual funds held in rabbi trusts	0	0
Derivative assets	0	0
Liabilities
Securities sold short	0	0
Mutual funds held in rabbi trusts	0	0
Derivative liabilities	0	0
Fair Value, Measurements, Recurring Basis
Assets
Trading securities	13,555	8,295
Investment securities available for sale	9,237,191	9,678,103
Mortgage loans held for sale	48,994	51,136
Other investments	11,789	11,172
Mutual funds and mutual funds held in rabbi trusts	49,119	42,659
Derivative assets	161,163	89,815
Liabilities
Securities sold short	2,362	3,370
Mutual funds held in rabbi trusts	34,768	27,944
Derivative liabilities	387,118	339,227
Fair Value, Measurements, Recurring Basis \| Collateralized mortgage obligations issued by U.S. Government sponsored enterprises
Assets
Trading securities	2,702	2,991
Investment securities available for sale	578,836	655,127
Fair Value, Measurements, Recurring Basis \| Other mortgage-backed securities
Assets
Trading securities	2,379	3,185
Fair Value, Measurements, Recurring Basis \| State and municipal securities
Assets
Trading securities	0	48
Fair Value, Measurements, Recurring Basis \| Asset-backed securities
Assets
Trading securities	8,399	2,071
Fair Value, Measurements, Recurring Basis \| Other Investments
Assets
Trading securities	75	0
Fair Value, Measurements, Recurring Basis \| U.S. Treasury securities
Assets
Investment securities available for sale	509,460	471,813
Fair Value, Measurements, Recurring Basis \| U.S. Government agency securities
Assets
Investment securities available for sale	47,506	48,798
Fair Value, Measurements, Recurring Basis \| Mortgage-backed securities issued by U.S. Government agencies
Assets
Investment securities available for sale	892,254	792,749
Fair Value, Measurements, Recurring Basis \| Mortgage-backed securities issued by U.S. Government sponsored enterprises
Assets
Investment securities available for sale	6,261,752	6,895,070
Fair Value, Measurements, Recurring Basis \| Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Assets
Investment securities available for sale	938,735	805,945
Fair Value, Measurements, Recurring Basis \| Corporate debt securities and other debt securities
Assets
Investment securities available for sale	8,648	8,601
Fair Value, Measurements, Recurring Basis \| Level 1
Assets
Trading securities	0	0
Investment securities available for sale	509,460	471,813
Mortgage loans held for sale	0	0
Other investments	0	0
Mutual funds and mutual funds held in rabbi trusts	49,119	42,659
Derivative assets	0	0
Liabilities
Securities sold short	2,362	3,370
Mutual funds held in rabbi trusts	34,768	27,944
Derivative liabilities	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| Collateralized mortgage obligations issued by U.S. Government sponsored enterprises
Assets
Trading securities	0	0
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| Other mortgage-backed securities
Assets
Trading securities	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| State and municipal securities
Assets
Trading securities	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| Asset-backed securities
Assets
Trading securities	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| Other Investments
Assets
Trading securities	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| U.S. Treasury securities
Assets
Investment securities available for sale	509,460	471,813
Fair Value, Measurements, Recurring Basis \| Level 1 \| U.S. Government agency securities
Assets
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| Mortgage-backed securities issued by U.S. Government agencies
Assets
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| Mortgage-backed securities issued by U.S. Government sponsored enterprises
Assets
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Assets
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| Corporate debt securities and other debt securities
Assets
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 2
Assets
Trading securities	13,555	8,295
Investment securities available for sale	8,727,731	9,206,290
Mortgage loans held for sale	48,994	51,136
Other investments	0	0
Mutual funds and mutual funds held in rabbi trusts	0	0
Derivative assets	161,163	89,815
Liabilities
Securities sold short	0	0
Mutual funds held in rabbi trusts	0	0
Derivative liabilities	387,118	339,227
Fair Value, Measurements, Recurring Basis \| Level 2 \| Collateralized mortgage obligations issued by U.S. Government sponsored enterprises
Assets
Trading securities	2,702	2,991
Investment securities available for sale	578,836	655,127
Fair Value, Measurements, Recurring Basis \| Level 2 \| Other mortgage-backed securities
Assets
Trading securities	2,379	3,185
Fair Value, Measurements, Recurring Basis \| Level 2 \| State and municipal securities
Assets
Trading securities	0	48
Fair Value, Measurements, Recurring Basis \| Level 2 \| Asset-backed securities
Assets
Trading securities	8,399	2,071
Fair Value, Measurements, Recurring Basis \| Level 2 \| Other Investments
Assets
Trading securities	75	0
Fair Value, Measurements, Recurring Basis \| Level 2 \| U.S. Treasury securities
Assets
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 2 \| U.S. Government agency securities
Assets
Investment securities available for sale	47,506	48,798
Fair Value, Measurements, Recurring Basis \| Level 2 \| Mortgage-backed securities issued by U.S. Government agencies
Assets
Investment securities available for sale	892,254	792,749
Fair Value, Measurements, Recurring Basis \| Level 2 \| Mortgage-backed securities issued by U.S. Government sponsored enterprises
Assets
Investment securities available for sale	6,261,752	6,895,070
Fair Value, Measurements, Recurring Basis \| Level 2 \| Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Assets
Investment securities available for sale	938,735	805,945
Fair Value, Measurements, Recurring Basis \| Level 2 \| Corporate debt securities and other debt securities
Assets
Investment securities available for sale	8,648	8,601
Fair Value, Measurements, Recurring Basis \| Level 3
Assets
Trading securities	0	0
Investment securities available for sale	0	0
Mortgage loans held for sale	0	0
Other investments	11,789	11,172
Mutual funds and mutual funds held in rabbi trusts	0	0
Derivative assets	0	0
Liabilities
Securities sold short	0	0
Mutual funds held in rabbi trusts	0	0
Derivative liabilities	0	0
Fair Value, Measurements, Recurring Basis \| Level 3 \| Collateralized mortgage obligations issued by U.S. Government sponsored enterprises
Assets
Trading securities	0	0
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 3 \| Other mortgage-backed securities
Assets
Trading securities	0	0
Fair Value, Measurements, Recurring Basis \| Level 3 \| State and municipal securities
Assets
Trading securities	0	0
Fair Value, Measurements, Recurring Basis \| Level 3 \| Asset-backed securities
Assets
Trading securities	0	0
Fair Value, Measurements, Recurring Basis \| Level 3 \| Other Investments
Assets
Trading securities	0	0
Fair Value, Measurements, Recurring Basis \| Level 3 \| U.S. Treasury securities
Assets
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 3 \| U.S. Government agency securities
Assets
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 3 \| Mortgage-backed securities issued by U.S. Government agencies
Assets
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 3 \| Mortgage-backed securities issued by U.S. Government sponsored enterprises
Assets
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 3 \| Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Assets
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 3 \| Corporate debt securities and other debt securities
Assets
Investment securities available for sale	$ 0	$ 0

Mutual Funds And Mutual Funds Held In Rabbi Trusts In Assets

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Mutual Funds And Mutual Funds Held In Rabbi Trusts In Liability

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Amount of 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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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Amount of investments classified as other.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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