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Data Type:	xbrli:monetaryItemType
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Interest rate of capital improvement revenue and special assessment bonds used to fund real estate development projects.

No definition available.

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Period Type:	instant

Term (in years) of capital improvement revenue and special assessment bonds used to fund real estate development projects.

No definition available.

Name:	ale_CommunityDevelopmentDistrictObligationBondTerminYears
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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Ownership percentage of property benefitied by a real estate development project funded by municipal capital improvement revenue and special assessment bonds.

No definition available.

Name:	ale_CommunityDevelopmentDistrictObligationOwnershipOfPropertyBenefited
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Data Type:	dtr-types:percentItemType
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Amount of any assets held either as collateral or by third parties that, upon the occurence of any triggering event or condition under the guarantee, can be obtained and liquidated to recover all or a portion of the amounts paid under the guarantee.

No definition available.

Name:	ale_GuarantorObligationsCollateralHeldDirectlyorbyThirdPartiesAmount
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Data Type:	xbrli:monetaryItemType
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The face amount of financial liabilities, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

No definition available.

Name:	us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability
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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.

No definition available.

Name:	us-gaap_GuaranteeObligationsLineItems
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Data Type:	xbrli:stringItemType
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Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI https://asc.fasb.org/extlink&oid=124440162&loc=d3e12069-110248

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

No definition available.

Name:	us-gaap_LettersOfCreditOutstandingAmount
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

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