DESCRIPTION OF PLAN - Narrative (Details) - EBP 002 Hours in Thousands	12 Months Ended
Dec. 31, 2025 USD ($) Hours year loan	Dec. 31, 2024 USD ($)
EBP, Description of Plan [Line Items]
Requisite service period	30 days
Participant contribution, automatic, annual increase deferral rate	1.00%
Requisite service period for discretionary matching contribution eligibility (in hours) \| Hours	1
Employer contribution maximum vesting age \| year	55
Employer contribution vesting percentage	100.00%
Forfeited nonvested account, decrease from administrative expense	$ 54,637	$ 46,349
Forfeited nonvested account, decrease from employer contribution	131,397	42,886
Forfeited nonvested account	$ 278,428	$ 221,944
Participant investment, maximum employer stock percentage	20.00%
Note receivable from participant, account, minimum borrowing, amount	$ 1,000
Note receivable from participant, new loan reduction, highest loan balance period	1 year
Note receivable from participant, account, maximum borrowing, to total account, percentage	50.00%
Note receivable from participant, maximum borrowing term	5 years
Note receivable from participant, number of maximum loans at any point in time \| loan	1
Contributions Tranche One
EBP, Description of Plan [Line Items]
Employer contribution, matching percentage	100.00%
Employer contribution, participant compensation matched, percentage	3.00%
Contributions Tranche Two
EBP, Description of Plan [Line Items]
Employer contribution, matching percentage	50.00%
Employer contribution, participant compensation matched, percentage	2.00%
Maximum
EBP, Description of Plan [Line Items]
Participant contribution, automatic, deferral rate	10.00%
Employer contribution, participant compensation matched, percentage	5.00%
Note receivable from participant, account, maximum borrowing, amount	$ 50,000
Benefit payments, mandatory distribution upon separation, vested account balance	$ 7,000
Minimum
EBP, Description of Plan [Line Items]
Participant contribution, automatic, deferral rate	5.00%
Note receivable from participant, account, maximum borrowing, amount	$ 10,000
Benefit payments, mandatory distribution upon separation, vested account balance	$ 1,000

EBP, Benefit Payments, Mandatory Distribution Upon Separation, Vested Account Balance

No definition available.

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Balance Type:	credit
Period Type:	instant

- Definition

EBP, Employer Contribution Maximum Vesting Age

+ References

No definition available.

+ Details

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Namespace Prefix:	sbsi_
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Period Type:	duration

- Definition

EBP, Employer Contribution Vesting Percentage

+ References

No definition available.

+ Details

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Namespace Prefix:	sbsi_
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Balance Type:	na
Period Type:	duration

- Definition

EBP, Note Receivable From Participant, Maximum Borrowing Term

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

EBP, Note Receivable From Participant, New Loan Reduction, Highest Loan Balance Period

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Note Receivable From Participant, Number Of Maximum Loans At Any Point In Time

+ References

No definition available.

+ Details

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Namespace Prefix:	sbsi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Participant Contribution, Automatic, Annual Increase Deferral Rate

+ References

No definition available.

+ Details

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Namespace Prefix:	sbsi_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Participant Investment, Maximum Employer Stock Percentage

+ References

No definition available.

+ Details

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Namespace Prefix:	sbsi_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Requisite Service Period

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Requisite Service Period, Discretionary Matching Contribution Eligibility

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

+ Details

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Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of employer matching contribution on eligible participant contribution to employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

+ Details

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Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of participant compensation eligible for employer matching contribution for participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

+ Details

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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of plan asset, in forfeited nonvested account, no longer allocated to participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of decrease in forfeited nonvested account of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) from administrative expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (j)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-04(5)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of decrease in forfeited nonvested account of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) from employer contribution.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478873/962-325-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (j)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-04(5)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

+ Details

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Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of maximum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow.

+ References

+ Details

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Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of maximum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow to total participant account balance.

+ References

+ Details

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Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of minimum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow.

+ References

+ Details

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Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of eligible compensation contributed for participant automatically enrolled in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

+ Details

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Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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- Details

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