LOANS AND ALLOWANCE FOR CREDIT LOSSES - Narrative (Details)	12 Months Ended
	Dec. 31, 2025 USD ($) loan	Dec. 31, 2024 USD ($) loan	Dec. 31, 2023 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 17,492,179,000	$ 17,005,937,000
Deferred origination fees, net	3,300,000	7,200,000
Deferred origination costs	5,400,000	9,600,000
Financing receivable, accrued interest excluded from amortized costs	80,300,000	78,800,000
Nonaccrual loans with no allowance for credit loss	18,000,000.0	$ 1,700,000
Number of loan modifications | loan		1
Extension of term of loan		1 year 6 months
Charge-off		$ 26,700,000
Number of loan modifications with payment default | loan		1
Financing receivable, collateral dependent, amount	112,374,000	$ 102,580,000
Provision for credit loss expense	69,038,000	46,785,000	$ 47,424,000
Spirit of Texas Bancshares, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred origination fees, net	1,377,000
Loans, Excluding Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit loss expense	69,038,000	46,785,000	47,424,000
Loans, Excluding Acquired Loans [Member] | Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit loss expense	$ 15,600,000
Number of credit relationships migrated to nonperforming | loan	2
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in process of foreclosure, amount	$ 4,400,000	4,000,000.0
Residential Real Estate | OREO Received in Full or Partial Satisfaction of Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Foreclosed assets and other real estate owned	3,600,000	1,300,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,688,639,000	2,695,329,000
Commercial | Spirit of Texas Bancshares, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred origination fees, net	378,000
Commercial | Loans, Excluding Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit loss expense	26,633,000	30,389,000	5,934,000
Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	13,771,225,000	13,391,531,000
Real Estate | Spirit of Texas Bancshares, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred origination fees, net	998,000
Real Estate | Loans, Excluding Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit loss expense	34,384,000	10,249,000	36,381,000
Unfunded commitments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Off-balance sheet, credit loss, liability, credit loss expense (reversal)	0	0	$ 16,300,000
Unfunded commitments, allowance for credit loss	25,600,000	25,600,000
Other commercial | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,289,968,000	7,912,336,000
Charge-off		18,800
Financing receivable, collateral dependent, amount	$ 66,266,000	$ 69,429,000
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, term of loan	1 year
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, term of loan	3 years