Fair Value Accounting (Financial Instruments Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Assets
Investment securities available for sale	$ 10,463,101	$ 10,918,329
Mortgage loans held for sale	111,992	108,198
Mortgage-backed securities issued by U.S. Government agencies
Assets
Investment securities available for sale	686,744	779,633
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Assets
Investment securities available for sale	822,878	939,623
Asset-backed securities
Assets
Investment securities available for sale	337,037	514,188
U.S. Treasury securities
Assets
Investment securities available for sale	394,586	117,838
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Assets
Investment securities available for sale	7,620,631	8,012,301
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Assets
Investment securities available for sale	530,796	481,744
Corporate debt securities and other debt securities
Assets
Investment securities available for sale	18,624	18,801
Level 1
Assets
Trading securities	0	0
Investment securities available for sale	394,586	117,838
Other investments	0	0
Mutual funds and mutual funds held in rabbi trusts	43,842	43,657
GGL/SBA loans servicing asset	0	0
Derivative assets	0	0
Liabilities
Trading liability for short positions	0	0
Mutual funds held in rabbi trusts	28,095	27,205
Derivative liabilities	0	0
Level 2
Assets
Trading securities	9,618	8,391
Investment securities available for sale	10,068,515	10,800,491
Other investments	0	0
Mutual funds and mutual funds held in rabbi trusts	0	0
GGL/SBA loans servicing asset	0	0
Derivative assets	160,545	191,708
Liabilities
Trading liability for short positions	389	200
Mutual funds held in rabbi trusts	0	0
Derivative liabilities	230,087	95,067
Level 3
Assets
Trading securities	0	0
Investment securities available for sale	0	0
Other investments	12,093	12,185
Mutual funds and mutual funds held in rabbi trusts	0	0
GGL/SBA loans servicing asset	3,451	3,233
Derivative assets	0	0
Liabilities
Trading liability for short positions	0	0
Mutual funds held in rabbi trusts	0	0
Derivative liabilities	1,776	3,535
Fair Value, Measurements, Recurring Basis
Assets
Trading securities	9,618	8,391
Investment securities available for sale	10,463,101	10,918,329
Mortgage loans held for sale	111,992	108,198
Other investments	12,093	12,185
Mutual funds and mutual funds held in rabbi trusts	43,842	43,657
GGL/SBA loans servicing asset	3,451	3,233
Derivative assets	160,545	191,708
Liabilities
Trading liability for short positions	389	200
Mutual funds held in rabbi trusts	28,095	27,205
Derivative liabilities	231,863	98,602
Fair Value, Measurements, Recurring Basis \| Mortgage-backed securities issued by U.S. Government agencies
Assets
Trading securities	0	197
Investment securities available for sale	686,744	779,633
Fair Value, Measurements, Recurring Basis \| Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Assets
Trading securities	483	671
Investment securities available for sale	822,878	939,623
Fair Value, Measurements, Recurring Basis \| Other mortgage-backed securities
Assets
Trading securities	3,362	0
Fair Value, Measurements, Recurring Basis \| State and municipal securities
Assets
Trading securities	414	560
Fair Value, Measurements, Recurring Basis \| Asset-backed securities
Assets
Trading securities	5,359	6,963
Investment securities available for sale	337,037	514,188
Fair Value, Measurements, Recurring Basis \| U.S. Treasury securities
Assets
Investment securities available for sale	394,586	117,838
Fair Value, Measurements, Recurring Basis \| U.S. Government agency securities
Assets
Investment securities available for sale	51,805	54,201
Fair Value, Measurements, Recurring Basis \| Mortgage-backed securities issued by U.S. Government sponsored enterprises
Assets
Investment securities available for sale	7,620,631	8,012,301
Fair Value, Measurements, Recurring Basis \| Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Assets
Investment securities available for sale	530,796	481,744
Fair Value, Measurements, Recurring Basis \| Corporate debt securities and other debt securities
Assets
Investment securities available for sale	18,624	18,801
Fair Value, Measurements, Recurring Basis \| Level 1
Assets
Trading securities	0	0
Investment securities available for sale	394,586	117,838
Mortgage loans held for sale	0	0
Other investments	0	0
Mutual funds and mutual funds held in rabbi trusts	43,842	43,657
GGL/SBA loans servicing asset	0	0
Derivative assets	0	0
Liabilities
Trading liability for short positions	0	0
Mutual funds held in rabbi trusts	28,095	27,205
Derivative liabilities	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| Mortgage-backed securities issued by U.S. Government agencies
Assets
Trading securities	0	0
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| Collateralized mortgage obligations issued by U.S. Government agencies or 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
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 1 \| U.S. Treasury securities
Assets
Investment securities available for sale	394,586	117,838
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 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	9,618	8,391
Investment securities available for sale	10,068,515	10,800,491
Mortgage loans held for sale	111,992	108,198
Other investments	0	0
Mutual funds and mutual funds held in rabbi trusts	0	0
GGL/SBA loans servicing asset	0	0
Derivative assets	160,545	191,708
Liabilities
Trading liability for short positions	389	200
Mutual funds held in rabbi trusts	0	0
Derivative liabilities	230,087	95,067
Fair Value, Measurements, Recurring Basis \| Level 2 \| Mortgage-backed securities issued by U.S. Government agencies
Assets
Trading securities	0	197
Investment securities available for sale	686,744	779,633
Fair Value, Measurements, Recurring Basis \| Level 2 \| Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Assets
Trading securities	483	671
Investment securities available for sale	822,878	939,623
Fair Value, Measurements, Recurring Basis \| Level 2 \| Other mortgage-backed securities
Assets
Trading securities	3,362	0
Fair Value, Measurements, Recurring Basis \| Level 2 \| State and municipal securities
Assets
Trading securities	414	560
Fair Value, Measurements, Recurring Basis \| Level 2 \| Asset-backed securities
Assets
Trading securities	5,359	6,963
Investment securities available for sale	337,037	514,188
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	51,805	54,201
Fair Value, Measurements, Recurring Basis \| Level 2 \| Mortgage-backed securities issued by U.S. Government sponsored enterprises
Assets
Investment securities available for sale	7,620,631	8,012,301
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	530,796	481,744
Fair Value, Measurements, Recurring Basis \| Level 2 \| Corporate debt securities and other debt securities
Assets
Investment securities available for sale	18,624	18,801
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	12,093	12,185
Mutual funds and mutual funds held in rabbi trusts	0	0
GGL/SBA loans servicing asset	3,451	3,233
Derivative assets	0	0
Liabilities
Trading liability for short positions	0	0
Mutual funds held in rabbi trusts	0	0
Derivative liabilities	1,776	3,535
Fair Value, Measurements, Recurring Basis \| Level 3 \| Mortgage-backed securities issued by U.S. Government agencies
Assets
Trading securities	0	0
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis \| Level 3 \| Collateralized mortgage obligations issued by U.S. Government agencies or 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
Investment securities available for sale	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 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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Fair value, before effects of master netting arrangements, of a financial liability or 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 liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Fair value portion of mortgage loans held-for-sale.

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Amount of investments classified as other.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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Fair value portion of liabilities pertaining to principal and customer trading transactions, or which may be incurred with the objective of generating a profit from short-term fluctuations in price as part of an entity's market-making, hedging and proprietary trading. Examples include, but are not limited to, short positions in securities, derivatives and commodities.

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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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