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Short-Term Borrowings - Narrative (Details) - Mortgage Backed Securities $ in Millions | Dec. 31, 2021 USD ($)
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Short-term Debt [Line Items] |
Amortized cost of securities pledged as collateral | $ 86.3
Carrying value of securities pledged as collateral | $ 88.4

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- Definition Pledged Financial Instruments, Not Separately Reported, Securities, Amortized Cost + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Pledged Financial Instruments, Not Separately Reported, Securities, Carrying Value + References No definition available. + Details
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Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |