XML 74 R83.htm IDEA: XBRL DOCUMENT v2.4.1.9
Allowance for Loan Losses - Recorded Investment in Commercial Loan Classes by Internally Assigned Risk Ratings (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan $ 2,892,522us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial $ 2,593,880us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
Total percentage of recorded investment in commercial loan 100.00%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage 100.00%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 2,780,315us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 2,430,926us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Total percentage of recorded investment in commercial loan 96.10%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 93.70%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 65,968us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 106,779us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Total percentage of recorded investment in commercial loan 2.30%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 4.10%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Substandard [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 46,239us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 56,175us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Total percentage of recorded investment in commercial loan 1.60%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 2.20%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Commercial Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 1,682,236us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember		 1,607,756us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Total percentage of recorded investment in commercial loan 100.00%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember		 100.00%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Commercial Real Estate [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 1,635,132us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 1,519,720us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Total percentage of recorded investment in commercial loan 97.20%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 94.50%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Commercial Real Estate [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 23,597us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 57,073us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Total percentage of recorded investment in commercial loan 1.40%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 3.60%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Commercial Real Estate [Member] | Substandard [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 23,507us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 30,963us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Total percentage of recorded investment in commercial loan 1.40%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 1.90%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Commercial and Industrial [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 994,138us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember		 842,449us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
Total percentage of recorded investment in commercial loan 100.00%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember		 100.00%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
Commercial and Industrial [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 948,663us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 792,029us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Total percentage of recorded investment in commercial loan 95.40%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 94.00%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Commercial and Industrial [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 30,357us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 34,085us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Total percentage of recorded investment in commercial loan 3.10%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 4.10%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Commercial and Industrial [Member] | Substandard [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 15,118us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 16,335us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Total percentage of recorded investment in commercial loan 1.50%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 1.90%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialAndIndustrialMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Commercial Construction [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 216,148us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember		 143,675us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
Total percentage of recorded investment in commercial loan 100.00%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember		 100.00%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
Commercial Construction [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 196,520us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 119,177us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Total percentage of recorded investment in commercial loan 90.90%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 82.90%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Commercial Construction [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan 12,014us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 15,621us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Total percentage of recorded investment in commercial loan 5.60%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 10.90%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Commercial Construction [Member] | Substandard [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total recorded investment in commercial loan $ 7,614us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 $ 8,877us-gaap_LoansAndLeasesReceivableGrossCarryingAmountCommercial
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Total percentage of recorded investment in commercial loan 3.50%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 6.20%stba_LoansAndLeasesReceivableGrossCarryingAmountCommercialPercentage
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stba_CommercialConstructionMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember