Represents the number of outstanding long-term FHLB advances.

No definition available.

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- Definition

Represents the number of outstanding short-term FHLB advances.

+ References

No definition available.

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Weighted average cost related to FHLB advances.

+ References

No definition available.

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
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- Definition

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.

+ References

No definition available.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

Interest expense incurred during the reporting period on long-term borrowings associated with Federal Home Loan Bank and Federal Reserve Bank advances.

+ References

No definition available.

+ Details

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- Definition

Interest expense incurred during the reporting period on short-term borrowings associated with Federal Home Loan Bank and Federal Reserve Bank advances.

+ References

No definition available.

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- Definition

Amount of addition (reduction) to the amount at which a liability could be incurred (settled) in a current transaction between willing parties.

+ References

No definition available.

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Borrowings - FHLB Advances - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) Loan	Dec. 31, 2018 USD ($) Loan	Dec. 31, 2017 USD ($)
Long Term Borrowing [Member] \| Federal Home Loan Bank Advances [Member] \| BancTrust [Member] \| Fair Market Value Adjustment [Member]
Debt Instrument [Line Items]
Long-term FHLB advances	$ 0	$ 0
Dallas [Member]
Debt Instrument [Line Items]
Additional debt instrument borrowing capacity	$ 3,178,000,000	$ 2,827,000,000
Dallas [Member] \| Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Number of outstanding long-term FHLB advances \| Loan	0	0
Dallas [Member] \| Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Number of outstanding short-term FHLB advances \| Loan	0
Atlanta and Dallas [Member]
Debt Instrument [Line Items]
Interest expense, short-term borrowings	$ 0	$ 4,400,000	$ 11,400,000
Atlanta and Dallas [Member] \| Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Interest expense, long-term	$ 5,000	$ 6,000	$ 566,000
Atlanta [Member] \| Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Number of outstanding long-term FHLB advances \| Loan	2	2
Weighted-average cost related to FHLB advances (in hundredths)	0.64%	0.63%
Weighted average remaining maturity	2 years 4 months 13 days	3 years 4 months 28 days
Atlanta [Member] \| Federal Home Loan Bank Advances [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate (in hundredths)	0.08%	0.08%
Atlanta [Member] \| Federal Home Loan Bank Advances [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate (in hundredths)	0.75%	0.75%
Atlanta [Member] \| Long Term Borrowing [Member] \| Federal Home Loan Bank Advances [Member] \| BancTrust [Member]
Debt Instrument [Line Items]
Long-term FHLB advances	$ 811,000	$ 879,000
Atlanta [Member] \| Long Term Borrowing [Member] \| Federal Home Loan Bank Advances [Member] \| BancTrust [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Long-term FHLB advances	135,000	153,000
Atlanta [Member] \| Long Term Borrowing [Member] \| Federal Home Loan Bank Advances [Member] \| BancTrust [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long-term FHLB advances	$ 676,000	$ 726,000