XML 135 R94.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Right-Of-Use Assets and Lease Liabilities - Narrative (Details) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 USD ($) lease director | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
Lessee, Lease, Description [Line Items] |  |  |
Number of lease contracts | lease | 51 |  |
Number of operating lease agreements | lease | 48 |  |
Number of financing leases | lease | 3 |  |
Operating lease expense | $ 4,221 | $ 3,850 | $ 3,980
Related party, lease with S&T Director |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Number of directors | director | 1 |  |
Operating lease expense | $ 200 |  |
Operating lease expense |  | $ 200 | $ 200
DNB |  |  |
Lessee, Lease, Description [Line Items] |  |  |
ROU asset acquired from DNB merger | $ 10,900 |  |

X
- Definition Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Right Of Use Assets + References No definition available. + Details
Name: | stba_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRightOfUseAssets
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Number Of Financing Leases + References No definition available. + Details
Name: | stba_NumberOfFinancingLeases
Namespace Prefix: | stba_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number Of Lease Contracts + References No definition available. + Details
Name: | stba_NumberOfLeaseContracts
Namespace Prefix: | stba_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of Operating Lease Agreements + References No definition available. + Details
Name: | stba_NumberofOperatingLeaseAgreements
Namespace Prefix: | stba_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Related Party Transaction, Number of Related Parties + References No definition available. + Details
Name: | stba_RelatedPartyTransactionNumberofRelatedParties
Namespace Prefix: | stba_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line. + References No definition available. + Details
Name: | us-gaap_LeaseAndRentalExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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

X
- Definition Amount of operating lease expense. Excludes sublease income. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918638-209977 + Details
Name: | us-gaap_OperatingLeaseExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_RelatedPartyTransactionAxis=stba_RelatedPartyLeaseAgreementWithSTDirectorMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=stba_DNBFinancialCorporationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |