Fair Value - Estimated fair value and related carrying amount, of the Company's financial instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financial liabilities:
Other derivative financial instruments (Mortgage banking related)	$ 402,256	$ 804,832
Carrying Amount
Financial assets:
Cash and cash equivalents	5,974,137	4,609,255
Trading securities	83,947	10,674
Investment securities	5,267,271	4,446,657
Loans held for sale	352,997	290,467
Loans, net of allowance for loan losses	24,085,005	24,206,825
Accrued interest receivable	105,865	107,601
Mortgage servicing rights	54,285	43,820
Interest rate swap - non-designated hedge	398,221	802,763
Other derivative financial instruments (mortgage banking related)	18,108	11,136
Financial liabilities:
Deposits	32,441,410	30,693,882
Federal funds purchased and securities sold under agreements to repurchase	878,581	779,666
Other borrowings	390,323	390,179
Accrued interest payable	8,498	7,103
Interest rate swap - non-designated hedge	399,625	804,832
Other derivative financial instruments (Mortgage banking related)	2,631
Fair Value
Financial assets:
Cash and cash equivalents	5,974,137	4,609,255
Trading securities	83,947	10,674
Investment securities	5,233,723	4,448,300
Loans held for sale	352,997	290,467
Loans, net of allowance for loan losses	24,421,405	24,757,859
Accrued interest receivable	105,865	107,601
Mortgage servicing rights	54,285	43,820
Interest rate swap - non-designated hedge	398,221	802,763
Other derivative financial instruments (mortgage banking related)	18,108	11,136
Financial liabilities:
Deposits	32,458,336	30,719,416
Federal funds purchased and securities sold under agreements to repurchase	878,581	779,666
Other borrowings	388,127	386,126
Accrued interest payable	8,498	7,103
Interest rate swap - non-designated hedge	399,625	804,832
Other derivative financial instruments (Mortgage banking related)	2,631
Commitments to extend credit \| Fair Value
Financial liabilities:
Commitments to extend credit	84,280	136,726
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	5,974,137	4,609,255
Investment securities	161,468	160,443
Significant Other Observable Inputs (Level 2)
Financial assets:
Trading securities	83,947	10,674
Investment securities	5,072,255	4,287,857
Loans held for sale	352,997	290,467
Accrued interest receivable	13,758	12,952
Interest rate swap - non-designated hedge	398,221	802,763
Other derivative financial instruments (mortgage banking related)	18,108	11,136
Financial liabilities:
Deposits	32,458,336	30,719,416
Federal funds purchased and securities sold under agreements to repurchase	878,581	779,666
Other borrowings	388,127	386,126
Accrued interest payable	8,498	7,103
Interest rate swap - non-designated hedge	399,625	804,832
Other derivative financial instruments (Mortgage banking related)	2,631
Significant Other Observable Inputs (Level 2) \| Commitments to extend credit
Financial liabilities:
Commitments to extend credit	84,280	136,726
Significant Unobservable Inputs (Level 3)
Financial assets:
Loans, net of allowance for loan losses	24,421,405	24,757,859
Accrued interest receivable	92,107	94,649
Mortgage servicing rights	$ 54,285	$ 43,820

Fair value of accrued interest payable as on date.

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Fair value of accrued interest receivable as on date.

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Fair value portion of arrangements to extend credit.

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The element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, the element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. The item represents residential mortgage servicing rights as presented on the statement of financial position which are due to the entity as of the balance sheet date.

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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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Fair value, after the 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 not subject to a master netting arrangement and not elected to be offset.

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Amount after offset of short term borrowing where a bank borrows, at the federal funds rate, from another bank and securities that an entity sells and agrees to repurchase at a specified date for a specified price.

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Fair value as of the balance sheet date of all derivative assets not designated as hedging instruments.

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Fair value as of the balance sheet date of all derivative liabilities not designated as hedging instruments.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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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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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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The carrying amount as of the balance sheet date for the aggregate of other miscellaneous borrowings owed by the reporting entity.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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