XML 55 R40.htm IDEA: XBRL DOCUMENT
v3.20.2

Business Combinations - Consideration, Assets Acquired and Liabilities Assumed (Details) - USD ($) |  |  |  | 6 Months Ended | 7 Months Ended
--- | --- | --- | --- | --- | ---
Jun. 30, 2020 | Dec. 31, 2019 | Nov. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2020
Fair Value of Assets Acquired |  |  |  |  |
Adjustments, Loans | $ (10,500,000) | $ (12,300,000) |  |  |
Goodwill | 373,289,000 | 371,621,000 |  | $ 373,289,000 | $ 373,289,000
Fair Value of Liabilities Assumed |  |  |  |  |
Goodwill | 373,289,000 | $ 371,621,000 |  | 373,289,000 | 373,289,000
As Recorded by DNB |  |  |  |  |
Fair Value of Assets Acquired |  |  |  |  |
Cash and cash equivalents |  |  | $ 64,119,000 |  |
Securities and other investments |  |  | 108,715,000 |  |
Loans |  |  | 917,127,000 |  |
Allowance for credit losses |  |  | (6,487,000) |  |
Goodwill |  |  | 15,525,000 |  |
Premises and equipment |  |  | 6,782,000 |  |
Accrued interest receivable |  |  | 4,138,000 |  |
Deferred income taxes |  |  | 2,017,000 |  |
Core deposits and other intangible assets |  |  | 269,000 |  |
Other assets |  |  | 24,883,000 |  |
Total Assets Acquired |  |  | 1,137,088,000 |  |
Fair Value of Liabilities Assumed |  |  |  |  |
Deposits |  |  | 966,263,000 |  |
Borrowings |  |  | 37,617,000 |  |
Accrued interest payable and other liabilities |  |  | 11,157,000 |  |
Total Liabilities Assumed |  |  | 1,015,037,000 |  |
Total Net Assets Acquired |  |  | 122,051,000 |  |
Identifiable Intangible Assets |  |  | 269,000 |  |
Goodwill |  |  | 15,525,000 |  |
DNB |  |  |  |  |
Fair Value of Assets Acquired |  |  |  |  |
Cash and cash equivalents | 64,119,000 |  | 64,119,000 | 64,119,000 | 64,119,000
Adjustments, Cash and cash equivalents |  |  | 0 |  | 0
Securities and other investments | 108,898,000 |  | 108,898,000 | 108,898,000 | 108,898,000
Adjustments, Securities and other investments |  |  | 183,000 |  | 0
Loans | 906,607,000 |  | 908,984,000 | 906,607,000 | 906,607,000
Adjustments, Loans |  |  | (8,143,000) | 2,500,000 | (2,377,000)
Allowance for credit losses | 0 |  | 0 | 0 | 0
Adjustments, Allowance for credit losses |  |  | 6,487,000 |  | 0
Goodwill | 85,842,000 |  | 84,175,000 | 85,842,000 | 85,842,000
Adjustments, Goodwill |  |  | (15,525,000) |  | 1,667,000
Premises and equipment | 14,872,000 |  | 14,872,000 | 14,872,000 | 14,872,000
Adjustments, Premises and equipment |  |  | 8,090,000 |  | 0
Accrued interest receivable | 4,138,000 |  | 4,138,000 | 4,138,000 | 4,138,000
Adjustments, Accrued interest receivable |  |  | 0 |  | 0
Deferred income taxes | (970,000) |  | (1,281,000) | (970,000) | (970,000)
Adjustments, Deferred income taxes |  |  | (3,298,000) |  | 311,000
Adjustments, Core deposits and other intangible assets |  |  | (269,000) |  |
Other assets | 20,679,000 |  | 20,605,000 | 20,679,000 | 20,679,000
Adjustments, Other assets |  |  | (4,278,000) |  | 74,000
Total Assets Acquired | 1,118,343,000 |  | 1,120,335,000 | 1,118,343,000 | 1,118,343,000
Adjustments, Total Assets Acquired |  |  | (16,753,000) |  | (1,992,000)
Fair Value of Liabilities Assumed |  |  |  |  |
Deposits | 967,265,000 |  | 967,265,000 | 967,265,000 | 967,265,000
Adjustments, Deposits |  |  | 1,002,000 |  | 0
Borrowings | 37,084,000 |  | 37,341,000 | 37,084,000 | 37,084,000
Adjustments, Borrowings |  |  | (276,000) |  | (257,000)
Accrued interest payable and other liabilities | 7,905,000 |  | 7,973,000 | 7,905,000 | 7,905,000
Adjustments, Accrued interest payable and other liabilities |  |  | (3,184,000) |  | (68,000)
Total Liabilities Assumed | 1,012,254,000 |  | 1,012,579,000 | 1,012,254,000 | 1,012,254,000
Adjustments, Total Liabilities Assumed |  |  | (2,458,000) |  | (325,000)
Total Net Assets Acquired | 106,089,000 |  | 107,756,000 | 106,089,000 | 106,089,000
Adjustments, Total Net Assets Acquired |  |  | (14,295,000) |  | (1,667,000)
Total Fair Value of Net Assets Acquired and Identified | 115,149,000 |  | 116,816,000 | 115,149,000 | 115,149,000
Adjustments, Total Fair Value of Net Assets Acquired and Identified |  |  |  |  | (1,667,000)
Cash |  |  | 360,000 |  |
Common stock |  |  | 200,631,000 |  |
Fair Value of Total Consideration |  |  | 200,991,000 |  |
Goodwill | 85,842,000 |  | 84,175,000 | 85,842,000 | 85,842,000
Core deposits | DNB |  |  |  |  |
Fair Value of Assets Acquired |  |  |  |  |
Core deposits and other intangible assets | 7,288,000 |  | 7,288,000 | 7,288,000 | 7,288,000
Adjustments, Core deposits and other intangible assets |  |  |  |  | 0
Fair Value of Liabilities Assumed |  |  |  |  |
Identifiable Intangible Assets | 7,288,000 |  | 7,288,000 | 7,288,000 | 7,288,000
Wealth management | DNB |  |  |  |  |
Fair Value of Assets Acquired |  |  |  |  |
Core deposits and other intangible assets | 1,772,000 |  | 1,772,000 | 1,772,000 | 1,772,000
Adjustments, Core deposits and other intangible assets |  |  |  |  | 0
Fair Value of Liabilities Assumed |  |  |  |  |
Identifiable Intangible Assets | $ 1,772,000 |  | $ 1,772,000 | $ 1,772,000 | $ 1,772,000

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accrued Interest Payable And Other Liabilities + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedInterestPayableAndOtherLiabilities
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accrued Interest Receivable + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedInterestReceivable
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Acquired Receivable, Fair Value + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAcquiredReceivableFairValue
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Allowance For Loan Losses + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAllowanceForLoanLosses
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Cash And Equivalents + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCashAndEquivalents
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Deferred Income Taxes + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredIncomeTaxes
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Deposits + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeposits
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Liabilities + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentLiabilities
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Marketable Securities + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentMarketableSecurities
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Noncurrent Liabilities, Long-Term Debt + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentNoncurrentLiabilitiesLongTermDebt
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Other Noncurrent Assets + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherNoncurrentAssets
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Tangible Assets + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentTangibleAssets
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Identifiable Tangible Assets And Liabilities Assumed, Net + References No definition available. + Details
Name: | stba_BusinessCombinationProvisionalInformationInitialAccountingIncompleteIdentifiableTangibleAssetsAndLiabilitiesAssumedNet
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Accrued Interest Payable And Other Liabilities + References No definition available. + Details
Name: | stba_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedInterestPayableAndOtherLiabilities
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Accrued Interest Receivable + References No definition available. + Details
Name: | stba_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedInterestReceivable
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Deferred Tax Assets (Liabilities) + References No definition available. + Details
Name: | stba_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsLiabilities
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Tangible Assets Acquired + References No definition available. + Details
Name: | stba_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedTangibleAssetsAcquired
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Allowance for Loan Losses + References No definition available. + Details
Name: | stba_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedAllowanceforLoanLosses
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits + References No definition available. + Details
Name: | stba_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedDeposits
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Business Combination, Recognized Identifiable Tangible Assets Acquired And Liabilities Assumed, Net + References No definition available. + Details
Name: | stba_BusinessCombinationRecognizedIdentifiableTangibleAssetsAcquiredAndLiabilitiesAssumedNet
Namespace Prefix: | stba_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair value of acquired receivable from business combination, excluding certain loans and debt securities acquired in transfer. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=121647850&loc=d3e4845-128472 + Details
Name: | us-gaap_BusinessCombinationAcquiredReceivablesFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6613-128477 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6578-128477 + Details
Name: | us-gaap_BusinessCombinationConsiderationTransferred1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of equity interests of the acquirer, including instruments or interests issued or issuable in consideration for the business combination. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6613-128477 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6578-128477 + Details
Name: | us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This element represents the amount of any measurement period adjustment (as defined) realized during the reporting period to items of consideration transferred in connection with a business combination for which the initial accounting was incomplete. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 4A -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121647850&loc=SL65897772-128472 + Details
Name: | us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This element represents the amount of any measurement period adjustment (as defined) realized during the reporting period to intangibles acquired in connection with a business combination for which the initial accounting was incomplete. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 4A -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121647850&loc=SL65897772-128472 + Details
Name: | us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition This element represents the amount of any measurement period adjustment (as defined) realized during the reporting period to property, plant, and equipment acquired in connection with a business combination for which the initial accounting was incomplete. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 4A -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121647850&loc=SL65897772-128472 + Details
Name: | us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentPropertyPlantAndEquipment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of currency on hand as well as demand deposits with banks or financial institutions, acquired at the acquisition date. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121647850&loc=d3e4845-128472 + Details
Name: | us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investments in debt and equity securities, including, but not limited to, held-to-maturity, trading and available-for-sale expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121647850&loc=d3e4845-128472 + Details
Name: | us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of intangible assets, excluding goodwill, acquired at the acquisition date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121647850&loc=d3e4845-128472 + Details
Name: | us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of liabilities assumed at the acquisition date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121647850&loc=d3e4845-128472 + Details
Name: | us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of long-term debt due after one year or the normal operating cycle, if longer, assumed at the acquisition date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121647850&loc=d3e4845-128472 + Details
Name: | us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of other assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121647850&loc=d3e4845-128472 + Details
Name: | us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The amount of property, plant, and equipment recognized as of the acquisition date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -URI http://asc.fasb.org/extlink&oid=121600890&loc=d3e2207-128464 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121647850&loc=d3e4845-128472 + Details
Name: | us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount recognized for assets, including goodwill, in excess of (less than) the aggregate liabilities assumed. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121647850&loc=d3e4845-128472 + Details
Name: | us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(10)(1)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=120320667&loc=SL49117168-202975 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266 + Details
Name: | us-gaap_Goodwill
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=116868678&loc=d3e961-128460 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=121556970&loc=d3e13816-109267 + Details
Name: | us-gaap_GoodwillPurchaseAccountingAdjustments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585 + Details
Name: | us-gaap_PaymentsToAcquireBusinessesGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=stba_DNBFinancialCorporationPreAcquisitionMember
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: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CoreDepositsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=stba_WealthManagementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |