Other Borrowings and Subordinated Notes and Debentures - Narrative (Details) - USD ($)	1 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Advances from Federal Home Loan Banks		$ 727,900,000	$ 953,200,000
Mortgage loans and investment securities securing FHLB advances		6,570,000,000
Additional advances from Federal Home Loan Bank		$ 4,720,000,000
Subordinated Debt
Debt Instrument [Line Items]
Face amount of debt	$ 330,000,000.0
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)		0.26161%
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		$ 37,057,000	$ 37,171,000
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%