XML 55 R45.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Loans and Loans Held for Sale - Restructured Loans By Type of Concession (Details) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2017 USD ($) contract | Sep. 30, 2016 USD ($) contract | Sep. 30, 2017 USD ($) contract | Sep. 30, 2016 USD ($) contract
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  | 15 |  | 14 |  | 33 |  | 52 |
Pre-Modification Outstanding Recorded Investment | [1] | $ 1,094 |  | $ 4,949 |  | $ 4,204 |  | $ 18,305 |
Post-Modification Outstanding Recorded Investment | [1] | 1,471 |  | 5,005 |  | 4,522 |  | 15,775 |
Total Difference in Recorded Investment |  | $ 377 |  | $ 56 |  | $ 318 |  | $ (2,530) |
Principal deferral |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  |  |  |  |  | 2 |  | 8 |
Pre-Modification Outstanding Recorded Investment | [1] |  |  |  |  | $ 529 |  | $ 9,026 |
Post-Modification Outstanding Recorded Investment | [1] |  |  |  |  | 529 |  | 6,574 |
Total Difference in Recorded Investment |  |  |  |  |  | $ 0 |  | $ (2,452) |
Chapter 7 bankruptcy |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract | [2] | 13 |  | 10 |  | 25 |  | 26 |
Pre-Modification Outstanding Recorded Investment | [1],[2] | $ 420 |  | $ 316 |  | $ 798 |  | $ 1,645 |
Post-Modification Outstanding Recorded Investment | [1],[2] | 255 |  | 313 |  | 627 |  | 1,597 |
Total Difference in Recorded Investment | [2] | $ (165) |  | $ (3) |  | $ (171) |  | $ (48) |
Interest rate reduction |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  | 0 |  | 1 |  | 0 |  | 1 |
Pre-Modification Outstanding Recorded Investment |  | $ 0 | [1] | $ 248 | [1] | $ 0 |  | $ 250 | [1]
Post-Modification Outstanding Recorded Investment |  | 0 | [1] | 250 | [1] | 0 |  | 248 | [1]
Total Difference in Recorded Investment |  | $ 0 |  | $ 2 |  | $ 0 |  | $ (2) |
Maturity date extension and interest rate reduction |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  | 0 |  | 1 |  | 3 |  | 2 |
Pre-Modification Outstanding Recorded Investment | [1] | $ 0 |  | $ 280 |  | $ 1,972 |  | $ 410 |
Post-Modification Outstanding Recorded Investment | [1] | 0 |  | 280 |  | 1,919 |  | 408 |
Total Difference in Recorded Investment |  | $ 0 |  | $ 0 |  | $ (53) |  | $ (2) |
Maturity date extension |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  | 2 |  | 2 |  | 3 |  | 15 |
Pre-Modification Outstanding Recorded Investment | [1] | $ 674 |  | $ 4,105 |  | $ 905 |  | $ 6,974 |
Post-Modification Outstanding Recorded Investment | [1] | 1,216 |  | 4,162 |  | 1,447 |  | 6,948 |
Total Difference in Recorded Investment |  | 542 |  | $ 57 |  | $ 542 |  | $ (26) |
Commercial Real Estate | Principal deferral |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  |  |  |  |  | 1 |  | 1 |
Pre-Modification Outstanding Recorded Investment | [1] |  |  |  |  | $ 100 |  | $ 4,721 |
Post-Modification Outstanding Recorded Investment | [1] |  |  |  |  | 100 |  | 2,270 |
Total Difference in Recorded Investment |  |  |  |  |  | $ 0 |  | $ (2,451) |
Commercial Real Estate | Chapter 7 bankruptcy |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract | [2] |  |  |  |  | 0 |  | 1 |
Pre-Modification Outstanding Recorded Investment | [1],[2] |  |  |  |  | $ 0 |  | $ 709 |
Post-Modification Outstanding Recorded Investment | [1],[2] |  |  |  |  | 0 |  | 681 |
Total Difference in Recorded Investment | [2] |  |  |  |  | $ 0 |  | $ (28) |
Commercial Real Estate | Interest rate reduction |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  |  |  | 1 |  | 0 |  | 1 |
Pre-Modification Outstanding Recorded Investment |  |  |  | $ 248 | [1] | $ 0 | [1] | $ 250 |
Post-Modification Outstanding Recorded Investment |  |  |  | 250 | [1] | 0 | [1] | 248 |
Total Difference in Recorded Investment |  | $ 0 |  | $ 2 |  | $ 0 |  | $ (2) |
Commercial Real Estate | Maturity date extension |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  | 1 |  | 0 |  | 1 |  | 0 |
Pre-Modification Outstanding Recorded Investment | [1] | $ 400 |  | $ 0 |  | $ 400 |  | $ 0 |
Post-Modification Outstanding Recorded Investment | [1] | 400 |  | 0 |  | 400 |  | 0 |
Total Difference in Recorded Investment |  | $ 0 |  | $ 0 |  | $ 0 |  | $ 0 |
Commercial and Industrial | Principal deferral |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  |  |  |  |  | 1 |  | 5 |
Pre-Modification Outstanding Recorded Investment | [1] |  |  |  |  | $ 429 |  | $ 985 |
Post-Modification Outstanding Recorded Investment | [1] |  |  |  |  | 429 |  | 985 |
Total Difference in Recorded Investment |  |  |  |  |  | $ 0 |  | $ 0 |
Commercial and Industrial | Maturity date extension and interest rate reduction |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  |  |  |  |  | 2 |  | 0 |
Pre-Modification Outstanding Recorded Investment | [1] |  |  |  |  | $ 1,799 |  | $ 0 |
Post-Modification Outstanding Recorded Investment | [1] |  |  |  |  | 1,799 |  | 0 |
Total Difference in Recorded Investment |  |  |  |  |  | $ 0 |  | $ 0 |
Commercial and Industrial | Maturity date extension |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  | 1 |  | 2 |  | 1 |  | 5 |
Pre-Modification Outstanding Recorded Investment | [1] | $ 274 |  | $ 4,105 |  | $ 274 |  | $ 4,860 |
Post-Modification Outstanding Recorded Investment | [1] | 816 |  | 4,162 |  | 816 |  | 4,891 |
Total Difference in Recorded Investment |  | $ 542 |  | $ 57 |  | $ 542 |  | $ 31 |
Commercial Construction | Maturity date extension |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  |  |  |  |  | 0 |  | 5 |
Pre-Modification Outstanding Recorded Investment | [1] |  |  |  |  | $ 0 |  | $ 1,357 |
Post-Modification Outstanding Recorded Investment | [1] |  |  |  |  | 0 |  | 1,302 |
Total Difference in Recorded Investment |  |  |  |  |  | $ 0 |  | $ (55) |
Residential Mortgage | Principal deferral |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  |  |  |  |  | 0 |  | 1 |
Pre-Modification Outstanding Recorded Investment | [1] |  |  |  |  | $ 0 |  | $ 3,273 |
Post-Modification Outstanding Recorded Investment | [1] |  |  |  |  | 0 |  | 3,273 |
Total Difference in Recorded Investment |  |  |  |  |  | $ 0 |  | $ 0 |
Residential Mortgage | Chapter 7 bankruptcy |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract | [2] | 1 |  | 3 |  | 2 |  | 7 |
Pre-Modification Outstanding Recorded Investment | [1],[2] | $ 148 |  | $ 153 |  | $ 181 |  | $ 439 |
Post-Modification Outstanding Recorded Investment | [1],[2] | 0 |  | 152 |  | 32 |  | 433 |
Total Difference in Recorded Investment | [2] | $ (148) |  | $ (1) |  | $ (149) |  | $ (6) |
Residential Mortgage | Maturity date extension and interest rate reduction |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  | 0 |  | 1 |  | 0 |  | 1 |
Pre-Modification Outstanding Recorded Investment | [1] | $ 0 |  | $ 280 |  | $ 0 |  | $ 280 |
Post-Modification Outstanding Recorded Investment | [1] | 0 |  | 280 |  | 0 |  | 280 |
Total Difference in Recorded Investment |  | $ 0 |  | $ 0 |  | $ 0 |  | $ 0 |
Residential Mortgage | Maturity date extension |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  |  |  |  |  | 0 |  | 1 |
Pre-Modification Outstanding Recorded Investment | [1] |  |  |  |  | $ 0 |  | $ 483 |
Post-Modification Outstanding Recorded Investment | [1] |  |  |  |  | 0 |  | 483 |
Total Difference in Recorded Investment |  |  |  |  |  | $ 0 |  | $ 0 |
Home Equity | Principal deferral |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  |  |  |  |  | 0 |  | 1 |
Pre-Modification Outstanding Recorded Investment | [1] |  |  |  |  | $ 0 |  | $ 47 |
Post-Modification Outstanding Recorded Investment | [1] |  |  |  |  | 0 |  | 46 |
Total Difference in Recorded Investment |  |  |  |  |  | $ 0 |  | $ (1) |
Home Equity | Chapter 7 bankruptcy |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract | [2] | 4 |  | 7 |  | 13 |  | 16 |
Pre-Modification Outstanding Recorded Investment | [1],[2] | $ 72 |  | $ 163 |  | $ 380 |  | $ 481 |
Post-Modification Outstanding Recorded Investment | [1],[2] | 70 |  | 161 |  | 375 |  | 470 |
Total Difference in Recorded Investment | [2] | $ (2) |  | $ (2) |  | $ (5) |  | $ (11) |
Home Equity | Maturity date extension and interest rate reduction |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  |  |  |  |  | 1 |  | 1 |
Pre-Modification Outstanding Recorded Investment | [1] |  |  |  |  | $ 173 |  | $ 130 |
Post-Modification Outstanding Recorded Investment | [1] |  |  |  |  | 120 |  | 128 |
Total Difference in Recorded Investment |  |  |  |  |  | $ (53) |  | $ (2) |
Home Equity | Maturity date extension |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract |  |  |  |  |  | 1 |  | 4 |
Pre-Modification Outstanding Recorded Investment | [1] |  |  |  |  | $ 231 |  | $ 274 |
Post-Modification Outstanding Recorded Investment | [1] |  |  |  |  | 231 |  | 272 |
Total Difference in Recorded Investment |  |  |  |  |  | $ 0 |  | $ (2) |
Installment and Other Consumer | Chapter 7 bankruptcy |  |  |  |  |  |  |  |  |
Financing Receivable, Modifications [Line Items] |  |  |  |  |  |  |  |  |
Number of Loans | contract | [2] | 8 |  | 0 |  | 10 |  | 2 |
Pre-Modification Outstanding Recorded Investment | [1],[2] | $ 200 |  | $ 0 |  | $ 237 |  | $ 16 |
Post-Modification Outstanding Recorded Investment | [1],[2] | 185 |  | 0 |  | 220 |  | 13 |
Total Difference in Recorded Investment | [2] | $ (15) |  | $ 0 |  | $ (17) |  | $ (3) |
[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] | Chapter 7 bankruptcy loans where the debt has been legally discharged through the bankruptcy court and not reaffirmed.

X
- Definition Financing receivable modifications difference in recorded investments. + References No definition available. + Details
Name: | stba_IncreaseDecreaseFinancingReceivableModificationsDifferenceInRecordedInvestments
Namespace Prefix: | stba_
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_FinancingReceivableModificationsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of financing receivables that have been modified by troubled debt restructurings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524 + Details
Name: | us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Post-modification amount of investment in financing receivables modified by troubled debt restructurings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524 + Details
Name: | us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Pre-modification amount of investment in financing receivables modified by troubled debt restructurings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524 + Details
Name: | us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=us-gaap_PaymentDeferralMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=stba_BankruptcyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=us-gaap_ContractualInterestRateReductionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=stba_InterestRateReductionandMaturityDateExtensionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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=stba_CommercialConstructionMember
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_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerBorrowerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |