XML 35 R62.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Allowance for Loan Losses - Summary of Allowance for Loan Losses and Recorded Investments (Detail) (USD $) | Mar. 31, 2015 | Dec. 31, 2014 | Mar. 31, 2014 | Dec. 31, 2013
--- | --- | --- | --- | ---
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment | $ 88,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 |  | $ 54,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment | 48,018,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment |  | 47,857,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment |  |  |
Total Allowance for Loan Losses | 48,106,000 us-gaap_LoansAndLeasesReceivableAllowance |  | 47,911,000 us-gaap_LoansAndLeasesReceivableAllowance |  | 46,616,000 us-gaap_LoansAndLeasesReceivableAllowance | 46,255,000 us-gaap_LoansAndLeasesReceivableAllowance
Portfolio Loans, Individually Evaluated for Impairment | 48,489,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment |  | 43,977,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment |  |  |
Portfolio Loans, Collectively Evaluated for Impairment | 4,635,209,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment |  | 3,824,769,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment |  |  |
Total Portfolio Loans | 4,683,698,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome | [1] | 3,868,746,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome | [1] |  |
Allowance for loan losses on acquired loans | 0 stba_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedAllowanceforLoanLosses |  |  |  |  |
Commercial Real Estate [Member] |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment | 39,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment | 19,032,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember |  | 20,164,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember |  |  |
Total Allowance for Loan Losses | 19,071,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember |  | 20,164,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember |  | 19,880,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | 18,921,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember
Portfolio Loans, Individually Evaluated for Impairment | 23,326,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember |  | 19,890,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember |  |  |
Portfolio Loans, Collectively Evaluated for Impairment | 2,129,087,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember |  | 1,662,346,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember |  |  |
Total Portfolio Loans | 2,152,413,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | [1] | 1,682,236,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateMember | [1] |  |
Commercial and Industrial [Member] |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment | 0 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment | 13,711,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember |  | 13,668,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember |  |  |
Total Allowance for Loan Losses | 13,711,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember |  | 13,668,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember |  | 13,979,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember | 14,433,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember
Portfolio Loans, Individually Evaluated for Impairment | 10,338,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember |  | 9,218,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember |  |  |
Portfolio Loans, Collectively Evaluated for Impairment | 1,200,715,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember |  | 984,920,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember |  |  |
Total Portfolio Loans | 1,211,053,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember | [1] | 994,138,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialAndIndustrialMember | [1] |  |
Commercial Construction [Member] |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment | 0 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment | 6,869,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember |  | 6,093,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember |  |  |
Total Allowance for Loan Losses | 6,869,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember |  | 6,093,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember |  | 5,183,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember | 5,374,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember
Portfolio Loans, Individually Evaluated for Impairment | 7,696,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember |  | 7,605,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember |  |  |
Portfolio Loans, Collectively Evaluated for Impairment | 278,470,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember |  | 208,543,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember |  |  |
Total Portfolio Loans | 286,166,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember | [1] | 216,148,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_CommercialConstructionMember | [1] |  |
Consumer Real Estate [Member] |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment | 41,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember |  | 43,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment | 6,682,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember |  | 6,290,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember |  |  |
Total Allowance for Loan Losses | 6,723,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember |  | 6,333,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember |  | 6,408,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember | 6,362,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember
Portfolio Loans, Individually Evaluated for Impairment | 7,080,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember |  | 7,202,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember |  |  |
Portfolio Loans, Collectively Evaluated for Impairment | 961,232,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember |  | 903,455,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember |  |  |
Total Portfolio Loans | 968,312,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember | [1] | 910,657,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_ConsumerRealEstateMember | [1] |  |
Other Consumer [Member] |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment | 8,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember |  | 11,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment | 1,724,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember |  | 1,642,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember |  |  |
Total Allowance for Loan Losses | 1,732,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember |  | 1,653,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember |  | 1,166,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember | 1,165,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember
Portfolio Loans, Individually Evaluated for Impairment | 49,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember |  | 62,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember |  |  |
Portfolio Loans, Collectively Evaluated for Impairment | 65,705,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember |  | 65,505,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember |  |  |
Total Portfolio Loans | 65,754,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember | [1] | 65,567,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = stba_OtherConsumerMember | [1] |  |
Fair Value Measurements [Member] |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for loan losses on acquired loans | $ 0 stba_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedAllowanceforLoanLosses / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |  |  |  |  |
[1] | (1) Includes acquired loans.

X
- Definition Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Allowance for Loan Losses + References No definition available. + Details
Name: | stba_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedAllowanceforLoanLosses
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524 + Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524 + Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The balance of financing receivables that were collectively evaluated for impairment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524 + Details
Name: | us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The balance of financing receivables that were individually evaluated for impairment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524 + Details
Name: | us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Subparagraph d -Article 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b)(1)(ii) -URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 6 -Section L -Subsection 1 + Details
Name: | us-gaap_LoansAndLeasesReceivableAllowance
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522 + Details
Name: | us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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