Other Borrowings and Subordinated Notes and Debentures - Narrative (Details)	1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($)	Sep. 30, 2022 USD ($) issuance	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Debt Instrument [Line Items]
Advances from Federal Home Loan Banks			$ 953,200,000	$ 838,500,000
Mortgage loans and investment securities securing FHLB advances			6,940,000,000
Additional advances from Federal Home Loan Bank			5,400,000,000
Early retirement of debt			$ 0	(365,000)	$ 0
Subordinated Debt
Debt Instrument [Line Items]
Face amount of debt	$ 330,000,000
Debt instrument, interest rate	5.00%		5.00%
Offering price, percent	100.00%
Debt issuance costs	$ 3,600,000
Subordinated Debt | LIBOR
Debt Instrument [Line Items]
Floating rate (as percent)	2.15%
Subordinated Debt | SOFR
Debt Instrument [Line Items]
Floating rate (as percent)			0.2616%
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			$ 37,171,000	$ 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) | SOFR
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) | SOFR | Spirit of Texas Bancshares, Inc.
Debt Instrument [Line Items]
Floating rate (as percent)			5.92%
Trust Preferred Securities
Debt Instrument [Line Items]
Face amount of debt		$ 56,200,000
Number of issuances of trust | issuance		5
Early retirement of debt		$ 365,000