Other Borrowings and Subordinated Notes and Debentures - Narrative (Details) - USD ($)	9 Months Ended	18 Months Ended
	Sep. 30, 2024	Sep. 30, 2024	Dec. 31, 2023	Apr. 30, 2022	Mar. 31, 2018
Debt Instrument [Line Items]
Advances from Federal Home Loan Banks	$ 1,030,000,000.00	$ 1,030,000,000.00	$ 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	$ 4,960,000,000	$ 4,960,000,000
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 | 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 Due
Debt Instrument [Line Items]
Debt instrument, interest rate	6.00%	6.00%
Long-term debt, gross	$ 37,085,000	$ 37,085,000	$ 37,171,000
Subordinated Debt | Subordinated Notes Payable Due | 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 Due | SOFR
Debt Instrument [Line Items]
Floating rate (as percent)	5.92%
Subordinated Debt | Subordinated Notes Payable Due | SOFR | Spirit of Texas Bancshares, Inc.
Debt Instrument [Line Items]
Floating rate (as percent)	5.92%