Non-Performing Assets Including Troubled Debt Restructurings (TDR) - Additional information (Details)	3 Months Ended	12 Months Ended
Mar. 31, 2021 USD ($) loan	Dec. 31, 2020 USD ($) loan
ALL reserve for TDR's	$ 143,000	$ 103,000
Increase in loan modifications to COVID-19	$ 569,000
Percentage of increase in balance of loan modifications	1.20%
Accrued interest receivable due to loan modification	$ 1,200,000
Number of loans \| loan	67	70
Commercial real estate and commercial loan portfolios
Number of loans \| loan	18
Second payment deferral
Balance of loans modified	$ 48,000,000
Complete payment deferrals
Number of loans \| loan	54	59

The amount of accrued interest receivable due to loan modification.

No definition available.

Name:	asrv_AccruedInterestReceivableFinancingReceivableLoanModificationFromCovid19
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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Allowance for loan and lease losses pertaining to troubled debt restructurings.

No definition available.

Name:	asrv_AllowanceForLoanAndLeaseLossesTroubledDebtRestructurings
Namespace Prefix:	asrv_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of financing receivable modified in response to COVID-19.

No definition available.

Name:	asrv_FinancingReceivableModificationCovid19
Namespace Prefix:	asrv_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of increase (decrease) in financing receivable modified in response to COVID-19.

No definition available.

Name:	asrv_FinancingReceivableModificationFromCovid19IncreaseDecrease
Namespace Prefix:	asrv_
Data Type:	xbrli:monetaryItemType
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Number of financing receivables that have been modified in response to COVID-19.

No definition available.

Name:	asrv_FinancingReceivableModificationsFromCovid19NumberOfContracts
Namespace Prefix:	asrv_
Data Type:	xbrli:integerItemType
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Percentage of increase (decrease) in financing receivable modified in response to COVID-19.

No definition available.

Name:	asrv_PercentageOfIncreaseDecreaseInFinancingReceivableLoanModificationFromCovid19
Namespace Prefix:	asrv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LoanRestructuringModificationAxis=asrv_SecondPaymentDeferralMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_PaymentDeferralMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: