Other Borrowings and Subordinated Notes and Debentures - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2024	Dec. 31, 2023	Apr. 30, 2022	Mar. 31, 2018
Debt Instrument [Line Items]
Advances from Federal Home Loan Banks	$ 853,200,000	$ 853,200,000	$ 953,200,000
Mortgage loans and investment securities securing FHLB advances	7,020,000,000.00	7,020,000,000.00
Additional advances from Federal Home Loan Bank	$ 5,330,000,000	$ 5,330,000,000
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 | LIBOR
Debt Instrument [Line Items]
Floating rate (as percent)		2.15%
Subordinated Debt | SOFR
Debt Instrument [Line Items]
Floating rate (as percent)	0.26161%	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%	6.00%
Long-term debt, gross	$ 37,142,000	$ 37,142,000	$ 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%	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%