Other Borrowings and Subordinated Notes and Debentures - Debt Components (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Mar. 31, 2018	Sep. 30, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 1,330,723	$ 1,722,104
FHLB advances, net of discount, due 2022 to 2034, 1.49% to 5.53% secured by real estate loans
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 934,147	1,306,143
FHLB advances, net of discount, due 2022 to 2034, 1.49% to 5.53% secured by real estate loans | Minimum
Debt Instrument [Line Items]
Fixed rate (as percent)		1.49%
FHLB advances, net of discount, due 2022 to 2034, 1.49% to 5.53% secured by real estate loans | Maximum
Debt Instrument [Line Items]
Fixed rate (as percent)		5.53%
Other long-term debt
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 30,625	31,830
Total other borrowings
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		964,772	1,337,973
Subordinated Notes
Debt Instrument [Line Items]
Fixed rate (as percent)	5.00%
Subordinated Notes | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)	2.15%
Subordinated Notes | Subordinated notes payable, due 4/1/2028, fixed-to-floating rate (fixed rate of 5.00% through 3/31/2023, floating rate of 2.15% above the three month LIBOR rate, reset quarterly)
Debt Instrument [Line Items]
Long-term debt, gross		$ 330,000	330,000
Fixed rate (as percent)		5.00%
Subordinated Notes | Subordinated notes payable, due 4/1/2028, fixed-to-floating rate (fixed rate of 5.00% through 3/31/2023, floating rate of 2.15% above the three month LIBOR rate, reset quarterly) | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		2.15%
Subordinated Notes | 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]
Long-term debt, gross		$ 37,313	0
Fixed rate (as percent)		6.00%
Subordinated Notes | 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]
Long-term debt, gross		$ 37,400
Fixed rate (as percent)		6.00%
Subordinated Notes | 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) | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Floating rate (as percent)		5.92%
Subordinated Notes | 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) | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | Spirit of Texas Bancshares, Inc.
Debt Instrument [Line Items]
Floating rate (as percent)		592.00%
Subordinated Notes | Trust preferred securities, due 9/15/2037, floating rate of 1.37% above the three month LIBOR rate, reset quarterly
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	10,310
Subordinated Notes | Trust preferred securities, due 9/15/2037, floating rate of 1.37% above the three month LIBOR rate, reset quarterly | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.37%
Subordinated Notes | Trust preferred securities, due 6/6/2037, floating rate of 1.57% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	10,310
Subordinated Notes | Trust preferred securities, due 6/6/2037, floating rate of 1.57% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.57%
Subordinated Notes | Trust preferred securities, due 12/15/2035, floating rate of 1.45% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	6,702
Subordinated Notes | Trust preferred securities, due 12/15/2035, floating rate of 1.45% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.45%
Subordinated Notes | Trust preferred securities, net of discount, due 6/15/2037, floating rate of 1.85% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	25,329
Subordinated Notes | Trust preferred securities, net of discount, due 6/15/2037, floating rate of 1.85% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.85%
Subordinated Notes | Trust preferred securities, net of discount, due 12/15/2036, floating rate of 1.85% above the three month LIBOR rate, reset quarterly, callable without penalty
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	3,041
Subordinated Notes | Trust preferred securities, net of discount, due 12/15/2036, floating rate of 1.85% above the three month LIBOR rate, reset quarterly, callable without penalty | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Floating rate (as percent)		1.85%
Total subordinated notes and debentures
Debt Instrument [Line Items]
Total other borrowings and subordinated debt		$ 365,951	384,131
Unamortized debt issuance costs		$ (1,362)	$ (1,561)