Fair Value Measurements (Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Available for sale securities	$ 5,647,315	$ 4,675,304
Held to maturity securities	1,408,961	1,568,009
Derivative financial instruments		23
Derivative financial instruments	47,042	11,953
Total Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	1,263,372	542,333
Available for sale securities	5,647,315	4,675,304
Held to maturity securities	1,517,688	1,611,004
Loans, net	22,062,765	21,044,079
Loans held for sale	103,566	55,864
Derivative financial instruments	168,822	54,446
Deposits	27,017,416	23,786,775
Federal funds purchased	250	195,450
Securities sold under agreements to repurchase	806,645	484,422
FHLB short-term borrowings	1,161,666	2,035,000
Long-term debt	434,597	226,098
Derivative financial instruments	56,278	21,089
Total Fair Value [Member] \| Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	1,263,372	542,333
Federal funds purchased	250	195,450
Securities sold under agreements to repurchase	806,645	484,422
FHLB short-term borrowings		2,035,000
Total Fair Value [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Available for sale securities	5,647,315	4,675,304
Held to maturity securities	1,517,688	1,611,004
Loans, net	91,819	182,377
Loans held for sale	103,566	55,864
Derivative financial instruments	168,822	54,446
FHLB short-term borrowings	1,161,666
Long-term debt	434,597	226,098
Derivative financial instruments	51,662	15,385
Total Fair Value [Member] \| Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Loans, net	21,970,946	20,861,702
Deposits	27,017,416	23,786,775
Derivative financial instruments	4,616	5,704
Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	1,263,372	542,333
Available for sale securities	5,647,315	4,675,304
Held to maturity securities	1,408,961	1,568,009
Loans, net	21,791,530	21,021,504
Loans held for sale	103,566	55,864
Derivative financial instruments	168,822	54,446
Deposits	27,030,659	23,803,575
Federal funds purchased	250	195,450
Securities sold under agreements to repurchase	806,645	484,422
FHLB short-term borrowings	1,100,000	2,035,000
Long-term debt	385,887	233,462
Derivative financial instruments	$ 56,278	$ 21,089

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value portion of short term borrowing where a bank borrows, at the federal funds rate, from another bank.

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Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

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Fair value portion of securities that an entity sells and agrees to repurchase at a specified date for a specified price.

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