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Amount of subordinated debentures, assumed at the acquisition date.

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Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages.

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Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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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.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount of the collateral pledged in support of federal home loan bank advances outstanding.

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Amount of advance from Federal Home Loan Bank (FHLBank) maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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The cash outflow from the repayment of long-term borrowing where a lender is placed in a lien position behind debt having a higher priority of repayment (senior) in case of liquidation of the entity's assets or underlying collateral.

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Other Borrowings and Subordinated Debentures (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 31, 2019	Oct. 30, 2019	Dec. 31, 2017
Debt Instrument [Line Items]
Repayments of subordinated debentures			$ 7,442,000	$ 0	$ 113,990,000
Advances from Federal Home Loan Banks			1,310,000,000
Mortgage loans and investment securities securing FHLB advances			5,600,000,000
Additional advances from Federal Home Loan Bank			2,700,000,000
FHLB advances outstanding			0
Assets			22,359,752,000	$ 21,259,143,000				$ 15,000,000,000
Federal Home Loan Bank Owns the Options (FOTO) Advances
Debt Instrument [Line Items]
Advances from Federal Home Loan Banks			$ 1,300,000,000
Federal Home Loan Bank Owns the Options (FOTO) Advances \| Minimum
Debt Instrument [Line Items]
Term of debt instrument			10 years
Federal Home Loan Bank Owns the Options (FOTO) Advances \| Maximum
Debt Instrument [Line Items]
Term of debt instrument			15 years
Landrum Company
Debt Instrument [Line Items]
Subordinated debentures						$ 33,917,000	$ 34,794,000
Repayments of subordinated debentures		$ 5,900,000
Subordinated Debt
Debt Instrument [Line Items]
Face amount of debt	$ 330,000,000.0
Debt instrument, interest rate	5.00%		5.00%
Debt issuance costs	$ 3,600,000
Subordinated Debt \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)	2.15%