XML 88 R54.htm IDEA: XBRL DOCUMENT
v3.20.1

Loans and Loans Held for Sale - Summary of Restructured Loans (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2020 | Mar. 31, 2019 | Dec. 31, 2019
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | [1] | $ 8,297 | [2] | $ 5,499 |
Commercial real estate |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | [1] | 2,210 |  |  |
Commercial and industrial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | [1] | 3,780 |  | 5,201 |
Commercial construction |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | [1] | 1,891 |  |  |
Consumer real estate |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | [1] | 415 |  |  |
Residential Mortgage |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | [1] |  |  | 49 |
Home equity |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans | [1] |  |  | $ 249 |
Performing TDRs |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 15,189 | [3] |  | $ 36,960
Performing TDRs | Commercial real estate |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 30 |  |  | 22,233
Performing TDRs | Commercial and industrial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 4,566 |  |  | 6,909
Performing TDRs | Commercial construction |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 3,316 |  |  | 1,425
Performing TDRs | Business banking |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 1,524 |  |  |
Performing TDRs | Consumer real estate |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 5,749 |  |  |
Performing TDRs | Residential Mortgage |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 2,013
Performing TDRs | Home equity |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 4,371
Performing TDRs | Other consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 4 |  |  |
Performing TDRs | Installment and other consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 9
Nonperforming TDRs |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 36,055 | [3] |  | 8,912
Nonperforming TDRs | Commercial real estate |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 28,973 |  |  | 6,713
Nonperforming TDRs | Commercial and industrial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 4,665 |  |  | 695
Nonperforming TDRs | Commercial construction |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 0 |  |  | 0
Nonperforming TDRs | Business banking |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 352 |  |  |
Nonperforming TDRs | Consumer real estate |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 2,064 |  |  |
Nonperforming TDRs | Residential Mortgage |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 822
Nonperforming TDRs | Home equity |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 678
Nonperforming TDRs | Other consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 0 |  |  |
Nonperforming TDRs | Installment and other consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 4
Total TDRs |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 51,243 | [3] |  | 45,872
Total TDRs | Commercial real estate |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 29,003 |  |  | 28,946
Total TDRs | Commercial and industrial |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 9,231 |  |  | 7,604
Total TDRs | Commercial construction |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 3,316 |  |  | 1,425
Total TDRs | Business banking |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 1,876 |  |  |
Total TDRs | Consumer real estate |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | 7,813 |  |  |
Total TDRs | Residential Mortgage |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 2,835
Total TDRs | Home equity |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | 5,049
Total TDRs | Other consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  | $ 4 |  |  |
Total TDRs | Installment and other consumer |  |  |  |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |  |  |  |
Restructured loans |  |  |  |  | $ 13
[1] | Excludes loans that were fully paid off or fully charged-off by period end. The pre-modification balance represents the balance outstanding prior to modification. The post-modification balance represents the outstanding balance at period end.
[2] | Refer to Note 1, Basis of Presentation for details of reclassification of our portfolio segments related to the adoption of ASU 2016-13 Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instrument.
[3] | Refer to Note 1, Basis of Presentation for details of reclassification of our portfolio segments related to the adoption of ASU 2016-13 Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.

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_FinancingReceivableModificationsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after troubled debt restructuring, of modified financing receivable. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524 + Details
Name: | us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stba_CommercialAndIndustrialMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stba_ConsumerRealEstateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_PerformingFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stba_BusinessBankingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stba_OtherConsumerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stba_InstallmentAndOtherConsumerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_NonperformingFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_FinanceReceivablesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |