XML 136 R123.htm IDEA: XBRL DOCUMENT
v3.20.4

Long-Term Borrowings and Subordinated Debt - Key Terms of Junior Subordinated Debt Securities (Details) - USD ($) $ in Thousands | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2020 | Apr. 01, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Junior Subordinated Debentures [Line Items] |  |  |  |
Junior subordinated debt securities | $ 64,083 |  | $ 64,277 | $ 45,619
Interest Rate at December 31, 2020 | 2.03% |  | 2.60% | 2.84%
Junior Subordinated Debt |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |
Junior subordinated debt securities | $ 34,750 |  | $ 34,753 | $ 25,000
Trust Preferred Securities |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |
Junior subordinated debt securities | 29,333 |  | $ 29,524 | $ 20,619
2001 Trust Preferred Securities | Trust Preferred Securities |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |
Junior subordinated debt securities | $ 5,155 |  |  |
Stated Maturity Date | Jul. 25, 2031 |  |  |
Optional redemption date at par | Any time after 7/25/2011 |  |  |
Regulatory Capital | Tier 1 |  |  |
Interest Rate at December 31, 2020 | 4.06% |  |  |
2001 Trust Preferred Securities | Trust Preferred Securities | LIBOR |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |
Interest Rate | 3.75% |  |  |
2005 Trust Preferred Securities | Trust Preferred Securities |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |
Junior subordinated debt securities | $ 4,124 |  |  |
Stated Maturity Date | May 23, 2035 |  |  |
Optional redemption date at par | Any time after 5/23/2010 |  |  |
Regulatory Capital | Tier 1 |  |  |
Interest Rate at December 31, 2020 | 1.98% |  |  |
2005 Trust Preferred Securities | Trust Preferred Securities | LIBOR |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |
Interest Rate | 1.77% |  |  |
2015 Junior Subordinated Debt | Junior Subordinated Debt |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |
Junior subordinated debt securities | $ 9,750 |  |  |
Stated Maturity Date | Mar. 06, 2025 |  |  |
Optional redemption date at par | Quarterly after 4/1/2020 |  |  |
Regulatory Capital | Tier 2 |  |  |
Fixed interest rate |  | 4.25% |  |
Interest Rate at December 31, 2020 | 4.25% |  |  |
2015 Junior Subordinated Debt | Junior Subordinated Debt | Prime Rate |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |
Interest Rate | 1.00% |  |  |
2006 Junior Subordinated Debt | Junior Subordinated Debt |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |
Junior subordinated debt securities | $ 25,000 |  |  |
Stated Maturity Date | Dec. 15, 2036 |  |  |
Optional redemption date at par | Any time after 9/15/2011 |  |  |
Regulatory Capital | Tier 2 |  |  |
Interest Rate at December 31, 2020 | 1.82% |  |  |
2006 Junior Subordinated Debt | Junior Subordinated Debt | LIBOR |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |
Interest Rate | 1.60% |  |  |
2008 Trust Preferred Securities | Trust Preferred Securities |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |
Junior subordinated debt securities | $ 20,619 |  |  |
Stated Maturity Date | Mar. 15, 2038 |  |  |
Optional redemption date at par | Any time after 3/15/2013 |  |  |
Regulatory Capital | Tier 1 |  |  |
Interest Rate at December 31, 2020 | 3.72% |  |  |
2008 Trust Preferred Securities | Trust Preferred Securities | LIBOR |  |  |  |
Junior Subordinated Debentures [Line Items] |  |  |  |
Interest Rate | 3.50% |  |  |

X
- Definition Debt instrument call date description. + References No definition available. + Details
Name: | stba_DebtInstrumentCallDateDescription
Namespace Prefix: | stba_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Junior Subordinated Debentures [Line Items] + References No definition available. + Details
Name: | stba_JuniorSubordinatedDebenturesLineItems
Namespace Prefix: | stba_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Regulatory capital. + References No definition available. + Details
Name: | stba_RegulatoryCapital
Namespace Prefix: | stba_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(2)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
Name: | us-gaap_DebtInstrumentMaturityDate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition Carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Junior Subordinated Notes, which have a lower priority than senior instruments, excluding current portion. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_JuniorSubordinatedLongTermNotes
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_LongTermDebtPercentageBearingFixedInterestRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Weighted average interest rate of long-term debt outstanding calculated at point in time. + References No definition available. + Details
Name: | us-gaap_LongtermDebtWeightedAverageInterestRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=us-gaap_JuniorSubordinatedDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=stba_TrustPreferredSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=stba_A2001TrustPreferredSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=stba_A2005TrustPreferredSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=stba_A2015JuniorSubordinatedDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=stba_A2006JuniorSubordinatedDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=stba_A2008TrustPreferredSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |