Other Borrowings and Subordinated Notes and Debentures - Narrative (Details) - USD ($)	6 Months Ended	27 Months Ended
	Jun. 30, 2025	Jun. 30, 2025	Dec. 31, 2024	Apr. 30, 2022	Mar. 31, 2018
Debt Instrument [Line Items]
Advances from FHLB	$ 617,800,000	$ 617,800,000	$ 727,900,000
Mortgage loans and investment securities securing FHLB advances	6,690,000,000	6,690,000,000
Additional advances from FHLB	$ 5,130,000,000	$ 5,130,000,000
Subordinated Debt
Debt Instrument [Line Items]
Face amount of debt					$ 330,000,000.0
Debt instrument, interest rate					5.00%
Offering price, percent					100.00%
Debt issuance costs					$ 3,600,000
Subordinated Debt | Subordinated Notes Payable Due
Debt Instrument [Line Items]
Debt instrument, interest rate	6.00%	6.00%
Long-term debt, gross	$ 37,000,000	$ 37,000,000	$ 37,057,000
Subordinated Debt | Spirit of Texas Bancshares, Inc. | Subordinated Notes Payable Due
Debt Instrument [Line Items]
Debt instrument, interest rate	6.00%	6.00%
Long-term debt, gross				$ 37,400,000
Subordinated Debt | LIBOR
Debt Instrument [Line Items]
Floating rate (as percent)		2.15%
Subordinated Debt | SOFR
Debt Instrument [Line Items]
Floating rate (as percent)		0.26161%
Subordinated Debt | SOFR | Subordinated Notes Payable Due
Debt Instrument [Line Items]
Floating rate (as percent)	5.92%
Subordinated Debt | SOFR | Spirit of Texas Bancshares, Inc. | Subordinated Notes Payable Due
Debt Instrument [Line Items]
Floating rate (as percent)	5.92%