XML 121 R105.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Deposits - Composition of Deposits and Interest Expenses (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Schedule Of Deposits And Borrowings Maturities [Line Items] |  |  |
Balance | $ 4,876,611 | $ 3,908,842 | $ 3,672,308
Interest Expense | 12,944 | 10,128 | 11,406
Noninterest-bearing Demand |  |  |
Schedule Of Deposits And Borrowings Maturities [Line Items] |  |  |
Balance | 1,227,766 | 1,083,919 | 992,779
Interest-bearing Demand |  |  |
Schedule Of Deposits And Borrowings Maturities [Line Items] |  |  |
Balance | 616,188 | 335,099 | 312,790
Interest Expense | 818 | 19 | 75
Money Market |  |  |
Schedule Of Deposits And Borrowings Maturities [Line Items] |  |  |
Balance | 605,184 | 376,612 | 281,403
Interest Expense | 1,299 | 572 | 446
Savings |  |  |
Schedule Of Deposits And Borrowings Maturities [Line Items] |  |  |
Balance | 1,061,265 | 1,027,095 | 994,805
Interest Expense | 1,712 | 1,607 | 1,735
Certificates of Deposit |  |  |
Schedule Of Deposits And Borrowings Maturities [Line Items] |  |  |
Balance | 1,366,208 | 1,086,117 | 1,090,531
Interest Expense | $ 9,115 | $ 7,930 | $ 9,150

X
- Definition Schedule Of Deposits And Borrowings Maturities [Line Items] + References No definition available. + Details
Name: | stba_ScheduleOfDepositsAndBorrowingsMaturitiesLineItems
Namespace Prefix: | stba_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others. + 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 210.9-03.12) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
Name: | us-gaap_Deposits
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Aggregate amount of interest expense on all deposits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.6) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 + Details
Name: | us-gaap_InterestExpenseDeposits
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | invest_InvestmentAxis=stba_NonInterestBearingDepositsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=us-gaap_InterestBearingDepositsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=stba_SavingsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |