XML 65 R55.htm IDEA: XBRL DOCUMENT
v3.4.0.3

Allowance for Loan Losses - Additional Information (Detail) - USD ($) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2016 | Dec. 31, 2015
Financing Receivable, Impaired [Line Items] |  |
Evaluation for impairment of substandard and nonaccrual commercial loans | $ 500,000.0 |
Impaired fiinancing receivables | $ 60,202,000 | $ 45,650,000
Minimum |  |
Financing Receivable, Impaired [Line Items] |  |
Loans considered nonperforming (in days) | 90 days |
Integrity Bancshares, Inc. |  |
Financing Receivable, Impaired [Line Items] |  |
Acquired loans that experienced credit deterioration since acquisition | $ 21,000,000 |

X
- Definition Minimum amount over which evaluation for impairment of substandard and nonaccrual commercial loans are made. + References No definition available. + Details
Name: | stba_MinimumAmountOverWhichEvaluationForImpairmentOfSubstandardAndNonaccrualCommercialLoansAreMade
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Period interest and principal of loan due treated as loans considered nonperforming. + References No definition available. + Details
Name: | stba_PeriodInterestAndPrincipalOfLoanDueTreatedAsLoansConsideredNonperforming
Namespace Prefix: | stba_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The recorded amount of loans and debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it was probable, at acquisition, that the investor would be unable to collect all contractually required payments receivable. They are deemed to be impaired since the acquisition and an allowance for credit losses has been recorded. Disclosure is gross of the allowance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5275-111524 + Details
Name: | us-gaap_CertainLoansAndDebtSecuritiesAcquiredInTransferWithRelatedAllowanceForCreditLossesDueToSubsequentImpairment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 14A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953550-111524 + Details
Name: | us-gaap_ImpairedFinancingReceivableRecordedInvestment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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