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Off-Balance-Sheet Arrangements, Commitments and Contingencies Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Operating lease right-of-use assets obtained in exchange for new operating lease liabilities	$ 0	$ 0	$ 0	$ 372,000
Unsettled trades to purchase securities	0	19,904,000	0	19,904,000	$ 0
Unsettled trades to sell securities	9,093,000	$ 0	9,093,000	$ 0	0
Unsettled Issuances of Brokered CDs	$ 0		$ 0		$ 0

X

- Definition

Amount of brokered CDs sold that were not settled by the end of the period. The amount recorded is the selling price including any accrued interest.

+ References

No definition available.

+ Details

Name:	sbsi_UnsettledIssuancesofBrokeredCDs
Namespace Prefix:	sbsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Amount of securities purchased that were not settled by the end of the period. The amount recorded is the purchase price including any accrued interest. This asset is collected upon delivery of the securities.

+ References

No definition available.

+ Details

Name:	sbsi_UnsettledTradesToPurchaseSecuritiesLiability
Namespace Prefix:	sbsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Amount of securities sold that were not settled by the end of the period. The amount recorded is the selling price including any accrued interest. This asset is collected upon delivery of the securities.

+ References

No definition available.

+ Details

Name:	sbsi_UnsettledTradesToSellSecurities
Namespace Prefix:	sbsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- References

No definition available.

+ Details

Name:	us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of increase in right-of-use asset obtained in exchange for operating lease liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 53
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479589/842-20-55-53

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (g)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-4

+ Details

Name:	us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration