Off-Balance-Sheet Arrangements, Commitments and Contingencies Narrative (Details)	1 Months Ended	3 Months Ended
Jan. 31, 2021 USD ($) contract	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets obtained in exchange for new operating lease liabilities		$ 0	$ 1,100,000
Lessee, Operating Lease, Number of Contracts \| contract	1
Operating lease ROU assets		14,751,000		$ 15,073,000
Unsettled trades to purchase securities		2,053,000	(23,473,000)	18,995,000
Unsettled trades to sell securities		47,019,000	$ 0	0
Unsettled Issuances of Brokered CDs		$ 0		$ 0
Operating lease
Lessee, Lease, Description [Line Items]
Operating lease ROU assets	$ 1,100,000

Lessee, Operating Lease, Number of Contracts

No definition available.

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

- 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

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

- 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

- 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

- 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

No definition available.

+ Details

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

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977

+ Details

Name:	us-gaap_OperatingLeaseRightOfUseAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 55
-Paragraph 53
-URI http://asc.fasb.org/extlink&oid=123414884&loc=SL77918982-209971

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (g)(2)
-URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918686-209980

+ Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: