Financing receivable loan modifications value due to CARES Act, not considered troubled debt restructuring.

No definition available.

Name:	alrs_FinancingReceivableLoanModificationsValueDueToCaresAct
Namespace Prefix:	alrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of financing receivable loan modifications due to CARES Act, not considered troubled debt restructuring.

+ References

No definition available.

+ Details

Name:	alrs_FinancingReceivableNumberOfLoanModificationsDueToCaresAct
Namespace Prefix:	alrs_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Typical loan deferral period under the CARES Act.

+ References

No definition available.

+ Details

Name:	alrs_PeriodOfLoanPrincipalAndInterestDeferrals
Namespace Prefix:	alrs_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of specific reserve for loans and losses allocated.

+ References

No definition available.

+ Details

Name:	alrs_SpecificReserveForLoansAndLeasesAllocated
Namespace Prefix:	alrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ 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=118936363&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

Loans and Allowance for Loan Losses - Troubled Debt Restructurings (Details) $ in Millions	3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) loan	Mar. 31, 2019 loan	Sep. 30, 2020 USD ($) loan	Dec. 31, 2019 USD ($)
Troubled debt restructuring
Number of loans modified as a troubled debt restructuring \| loan	0
Number of loan modifications not considered TDRs, in connection with CARES Act \| loan	552		552
Loan modifications not considered TDRS, in connection with CARES Act \| $	$ 151.4		$ 151.4
Maximum
Troubled debt restructuring
Typical loan deferral period under the CARES Act			90 days
Interest Rate Below Market Reduction
Troubled debt restructuring
Number of loans modified as a troubled debt restructuring \| loan		1
Carrying value of restructured loan \| $				$ 0.2
Specific reserve for loan losses allocated \| $				$ 0.0
Second Deferral
Troubled debt restructuring
Number of loan modifications not considered TDRs, in connection with CARES Act \| loan	27		27
Loan modifications not considered TDRS, in connection with CARES Act \| $	$ 16.9		$ 16.9
First Deferral
Troubled debt restructuring
Number of loan modifications not considered TDRs, in connection with CARES Act \| loan	56		56
Loan modifications not considered TDRS, in connection with CARES Act \| $	$ 12.0		$ 12.0