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Debt Instrument, Offering Price, Percent

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

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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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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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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Other Borrowings and Subordinated Notes and Debentures - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Advances from Federal Home Loan Banks		$ 1,000,000,000	$ 838,500,000
Mortgage loans and investment securities securing FHLB advances		6,900,000,000
Additional advances from Federal Home Loan Bank		$ 5,600,000,000
Subordinated Debt
Debt Instrument [Line Items]
Face amount of debt	$ 330,000,000
Debt instrument, interest rate	5.00%
Offering price, percent	100.00%
Debt issuance costs	$ 3,600,000
Subordinated Debt \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)	2.15%
Subordinated Debt \| Subordinated notes payable, net of premium adjustments, due 7/31/2030, fixed-to-floating rate (fixed rate of 6.00% through 7/30/2025, floating rate of 5.92% above the three month SOFR rate, reset quarterly)
Debt Instrument [Line Items]
Debt instrument, interest rate		6.00%
Long-term debt, gross		$ 37,256,000	$ 37,285,000
Subordinated Debt \| Subordinated notes payable, net of premium adjustments, due 7/31/2030, fixed-to-floating rate (fixed rate of 6.00% through 7/30/2025, floating rate of 5.92% above the three month SOFR rate, reset quarterly) \| Spirit of Texas Bancshares, Inc.
Debt Instrument [Line Items]
Debt instrument, interest rate		6.00%
Long-term debt, gross		$ 37,400,000
Subordinated Debt \| Subordinated notes payable, net of premium adjustments, due 7/31/2030, fixed-to-floating rate (fixed rate of 6.00% through 7/30/2025, floating rate of 5.92% above the three month SOFR rate, reset quarterly) \| Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Floating rate (as percent)		5.92%
Subordinated Debt \| Subordinated notes payable, net of premium adjustments, due 7/31/2030, fixed-to-floating rate (fixed rate of 6.00% through 7/30/2025, floating rate of 5.92% above the three month SOFR rate, reset quarterly) \| Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate \| Spirit of Texas Bancshares, Inc.
Debt Instrument [Line Items]
Floating rate (as percent)		592.00%