XML 78 R62.htm IDEA: XBRL DOCUMENT
v3.20.2

Allowance for Credit Losses - Additional Information (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2020 | Jun. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019 | Dec. 31, 2018 | Jan. 01, 2020 | Jun. 30, 2019
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Accounting Standards Update [Extensible List] |  |  |  | us-gaap:AccountingStandardsUpdate201613Member |  | us-gaap:AccountingStandardsUpdate201613Member | us-gaap:AccountingStandardsUpdate201602Member |  |
Adjustment to allowance for credit loss | $ 120,998 | $ 114,609 | $ 62,115 | $ 120,998 | $ 62,115 | $ 62,224 | $ 60,996 | $ 62,224 | $ 61,479
Charge-offs | 13,667 |  | 4,700 | 93,416 | 13,391 |  |  |  |
Total loans | 7,273,870 |  |  | 7,273,870 |  | 7,074,928 |  | 7,074,928 |
Restructured loans | 4,562 |  | 25,800 | 11,586 | 36,712 |  |  |  |
Reserve | 19,302 |  | 4,913 | 123,564 | 12,767 |  |  |  |
Increase (decrease) change in qualitative reserve | (13,500) |  |  | $ 15,800 |  |  |  |  |
Forecast period |  |  |  | 2 years |  |  |  |  |
Portfolio loans, net of unearned income | 7,394,868 |  |  | $ 7,394,868 |  | 7,137,152 |  |  |
Senior Lien |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Reserve | 3,400 |  |  |  |  |  |  |  |
Commercial |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income | 5,810,034 |  |  | 5,810,034 |  | 5,512,796 |  |  |
Commercial | Special mention |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income |  |  |  |  |  | 103,878 |  |  |
Commercial | Substandard |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income |  |  |  |  |  | 152,651 |  |  |
Nonperforming |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Restructured loans |  |  |  | 18,648 |  | 8,912 |  |  |
Portfolio loans, net of unearned income | 84,072 |  |  | 84,072 |  |  |  |  |
Impact of ASU 2016-13 Adoption |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Adjustment to allowance for credit loss |  |  |  |  |  | 27,352 |  | 27,353 |
Total loans |  |  |  |  |  |  |  | (27,353) |
S&T Legacy Loans | Impact of ASU 2016-13 Adoption |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Adjustment to allowance for credit loss |  |  |  |  |  |  |  | 8,200 |
Commercial and industrial | Commercial |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Adjustment to allowance for credit loss | 14,211 | 19,164 | 14,367 | 14,211 | 14,367 | 15,681 | 11,596 |  | 13,227
Charge-offs | 1,196 |  | 1,467 | 72,692 | 8,379 |  |  |  |
Restructured loans | 4,022 |  | 1,527 | 5,381 | 5,860 |  |  |  |
Reserve | (4,155) |  | 2,397 | 62,949 | 10,432 |  |  |  |
Portfolio loans, net of unearned income | 1,818,649 |  |  | 1,818,649 |  | 1,480,529 |  | 1,720,833 |
Commercial and industrial | Commercial | Special mention |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income | 74,919 |  |  | 74,919 |  |  |  |  |
Commercial and industrial | Commercial | Substandard |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income | 36,261 |  |  | 36,261 |  |  |  |  |
Commercial and industrial | Nonperforming | Commercial |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Restructured loans |  |  |  | 1,549 |  | 695 |  |  |
Portfolio loans, net of unearned income | 5,686 |  |  | 5,686 |  |  |  |  |
Commercial and industrial | Impact of ASU 2016-13 Adoption | Commercial |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Adjustment to allowance for credit loss |  |  |  |  |  | 7,853 |  | 9,900 |
Portfolio loans, net of unearned income |  |  |  |  |  |  |  | (262,292) |
Customer fraud, check kiting |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Charge-offs |  | 58,700 |  |  |  |  |  |  |
Customer fraud |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Charge-offs |  | 4,200 |  |  |  |  |  |  |
Total loans |  | 15,100 |  |  |  |  |  |  |
Customer fraud | Nonperforming |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Restructured loans |  |  |  | 10,900 |  |  |  |  |
CARES Act, Paycheck Protection Program Loans |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Total loans | 550,100 |  |  | 550,100 |  |  |  |  |
Restructured loans |  |  |  | 350,000 |  |  |  |  |
ACL provision, COVID-19 assessment, revised forecast | (13,300) |  |  | 12,700 |  |  |  |  |
Increase (decrease) in ACL provision, COVID-19 assessment, changes in current conditions | (200) |  |  | 3,100 |  |  |  |  |
CARES Act, Paycheck Protection Program Loans | Commercial |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Total loans | 550,100 |  |  | 550,100 |  |  |  |  |
Customer fraud, commercial real estate | Commercial |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Total loans |  | 14,300 |  |  |  |  |  |  |
Customer fraud, line of credit |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Total loans |  | 800 |  |  |  |  |  |  |
Business banking | Commercial |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Adjustment to allowance for credit loss | 14,792 | 14,404 |  | 14,792 |  | 0 |  |  |
Charge-offs | 1,748 |  |  | 2,469 |  |  |  |  |
Reserve | 2,072 |  |  | 4,197 |  |  |  |  |
ACL provision, COVID-19 assessment | 2,000 |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income | 1,015,951 |  |  | 1,015,951 |  | 846,790 |  | 0 |
Business banking | Commercial | Special mention |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income | 11,789 |  |  | 11,789 |  |  |  |  |
Business banking | Commercial | Substandard |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income | 39,422 |  |  | 39,422 |  |  |  |  |
Business banking | Nonperforming | Commercial |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Restructured loans |  |  |  | 441 |  |  |  |  |
Portfolio loans, net of unearned income | 18,081 |  |  | 18,081 |  |  |  |  |
Business banking | Impact of ASU 2016-13 Adoption | Commercial |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Adjustment to allowance for credit loss |  |  |  |  |  | 12,898 |  |  |
Portfolio loans, net of unearned income |  |  |  |  |  |  |  | 1,092,908 |
Commercial real estate | Commercial |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Adjustment to allowance for credit loss | 71,554 | $ 57,730 | 31,830 | 71,554 | 31,830 | 30,577 | $ 33,707 |  | $ 32,836
Charge-offs | 10,187 |  | 2,304 | 16,229 | 2,833 |  |  |  |
Restructured loans | 171 |  | 23,784 | 2,381 | 29,747 |  |  |  |
Reserve | 23,839 |  | $ 1,292 | 52,185 | $ 822 |  |  |  |
Portfolio loans, net of unearned income | 2,818,227 |  |  | 2,818,227 |  | 3,059,592 |  | 3,416,518 |
Commercial real estate | Commercial | Hotel |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income | $ 243,000 |  |  | $ 243,000 |  |  |  |  |
Amount deferred (as a percent) | 95.00% |  |  | 95.00% |  |  |  |  |
Commercial real estate | Commercial | Special mention |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income | $ 168,743 |  |  | $ 168,743 |  |  |  |  |
Commercial real estate | Commercial | Special mention | Hotel |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income | 92,900 |  |  | 92,900 |  |  |  |  |
Commercial real estate | Commercial | Substandard |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income | 203,543 |  |  | 203,543 |  |  |  |  |
Commercial real estate | Commercial | Substandard | Hotel |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Portfolio loans, net of unearned income | 126,600 |  |  | 126,600 |  |  |  |  |
Commercial real estate | Nonperforming | Commercial |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Restructured loans |  |  |  | 14,504 |  | 6,713 |  |  |
Portfolio loans, net of unearned income | $ 47,095 |  |  | $ 47,095 |  |  |  |  |
Commercial real estate | Impact of ASU 2016-13 Adoption | Commercial |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Adjustment to allowance for credit loss |  |  |  |  |  | $ 4,810 |  |  |
Portfolio loans, net of unearned income |  |  |  |  |  |  |  | (470,199) |
DNB | Impact of ASU 2016-13 Adoption |  |  |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |  |  |
Adjustment to allowance for credit loss |  |  |  |  |  |  |  | $ 9,300 |

X
- Definition Financing Receivable, Allowance For Credit Loss, Forecast Period + References No definition available. + Details
Name: | stba_FinancingReceivableAllowanceForCreditLossForecastPeriod
Namespace Prefix: | stba_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Financing Receivable, Allowance For Credit Loss, Increase (Decrease) For Pandemic Forecast + References No definition available. + Details
Name: | stba_FinancingReceivableAllowanceForCreditLossIncreaseDecreaseForPandemicForecast
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Financing Receivable, Allowance For Credit Loss, Increase (Decrease) For Risk Component + References No definition available. + Details
Name: | stba_FinancingReceivableAllowanceForCreditLossIncreaseDecreaseForRiskComponent
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Financing Receivable, Credit Loss, Expense (Reversal), COVID-19 Assessment, Forecast Component + References No definition available. + Details
Name: | stba_FinancingReceivableCreditLossExpenseReversalCOVID19AssessmentForecastComponent
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Financing Receivable, Percent Deferred + References No definition available. + Details
Name: | stba_FinancingReceivablePercentDeferred
Namespace Prefix: | stba_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Indicates amendment to accounting standards. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (g)(1) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 65 -Paragraph 15 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 10 -Section 65 -Paragraph 4 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121646688&loc=SL121648383-210437 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 65 -Paragraph 15 -Subparagraph (f)(1) -URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (g)(2)(i) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 65 -Paragraph 15 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 10 -Section 65 -Paragraph 4 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121646688&loc=SL121648383-210437 Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 65 -Paragraph 15 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333 Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (h)(2) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 12: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 13: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 10 -Section 65 -Paragraph 4 -Subparagraph (e)(3) -URI http://asc.fasb.org/extlink&oid=121646688&loc=SL121648383-210437 Reference 14: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 65 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333 Reference 15: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794 Reference 16: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 17: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(4) -URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794 Reference 18: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794 Reference 19: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (g)(2)(iv) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 20: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (g)(2)(iii) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 21: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 22: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 65 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333 Reference 23: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 65 -Paragraph 15 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333 Reference 24: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794 Reference 25: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 10 -Section 65 -Paragraph 4 -Subparagraph (e)(4) -URI http://asc.fasb.org/extlink&oid=121646688&loc=SL121648383-210437 Reference 26: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 10 -Section 65 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121646688&loc=SL121648383-210437 Reference 27: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 65 -Paragraph 15 -Subparagraph (g)(2) -URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333 Reference 28: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (f)(1) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 29: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 10 -Section 65 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121646688&loc=SL121648383-210437 Reference 30: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (g)(2)(ii) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 31: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 65 -Paragraph 8 -Subparagraph (d)(2) Reference 32: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 65 -Paragraph 8 -Subparagraph (d)(3) + Details
Name: | us-gaap_AccountingStandardsUpdateExtensibleList
Namespace Prefix: | us-gaap_
Data Type: | srt-types:extensibleListItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(7)(2)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121599878&loc=SL82895884-210446 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 + Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

X
- Definition Amount of increase (decrease) in allowance for credit loss on financing receivable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 + Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLossesPeriodIncreaseDecrease
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of writeoff of financing receivable, charged against allowance for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448 + Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, after troubled debt restructuring, of modified financing receivable. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524 + Details
Name: | us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, before allowance for credit loss, of financing receivable. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919230-210447 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 80 -URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922355-210448 + Details
Name: | us-gaap_NotesReceivableGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919230-210447 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(3)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522 + Details
Name: | us-gaap_NotesReceivableNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of credit loss expense (reversal of expense) for financing receivable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(11)) -URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260 + Details
Name: | us-gaap_ProvisionForLoanLossesExpensed
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_LienCategoryAxis=us-gaap_SeniorLienMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=us-gaap_SpecialMentionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=us-gaap_SubstandardMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_NonperformingFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CumulativeEffectPeriodOfAdoptionAxis=srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stba_STLegacyLoanMember
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_CustomerFraudCheckKitingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stba_CustomerFraudMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stba_PaycheckProtectionProgramLoanCARESActMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stba_CustomerFraudCommercialRealEstateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stba_CustomerFraudLineOfCreditMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=stba_BusinessBankingMember
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: |

X
- Details
Name: | us-gaap_CollateralAxis=srt_HotelMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=stba_DNBFinancialCorporationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |