Name:	ale_CapitalImprovementRevenuespecialAssessmentBondsAnnualAssessmentsBasedOnOwnershipPercentage
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Issue date of municipal bonds used to fund a development project.

No definition available.

Name:	ale_CapitalImprovementRevenuespecialAssessmentBondsDateIssued
Namespace Prefix:	ale_
Data Type:	us-types:dateStringItemType
Balance Type:	na
Period Type:	instant

Interest rate of municipal bonds used to fund a development project.

No definition available.

Name:	ale_CapitalImprovementRevenuespecialAssessmentBondsInterestRate
Namespace Prefix:	ale_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Ownership percentage of property benefited by a development project funded by municipal bonds.

No definition available.

Name:	ale_CapitalImprovementRevenuespecialAssessmentBondsOwnershipPercentageOfBenefitedProperty
Namespace Prefix:	ale_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Term in years of municipal bonds used to fund a development project.

No definition available.

Name:	ale_CapitalImprovementRevenuespecialAssessmentBondsTermYears
Namespace Prefix:	ale_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Estimated costs remaining on performance and maintenance obligations.

No definition available.

Name:	ale_PerformanceAndMaintenanceObligations
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of surety bonds that are available for future payment obligations.

No definition available.

Name:	ale_SuretyBondsOutstanding
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of letter of credit issued in addition to surety bond to secure performance obligation.

No definition available.

Name:	ale_TotalAmountOfLetterOfCreditSecuredInAdditionToSuretyBondsForReclamationLiability
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Total current estimated liability for performance obligation.

No definition available.

Name:	ale_TotalCurrentEstimatedReclamationLiability
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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

Including the current and noncurrent portions, carrying value as of the balance sheet date of a type of municipal bond typically used to fund a development project. Also called special assessment limited liability bond, special district bond, special purpose bond, special tax bond and community development obligation. Interest owed to lenders is paid by taxes levied on the community benefiting from the particular bond-funded project. For example, if a bond of this sort was issued to pay for sidewalks to be repaved in a certain community, an additional tax would be levied on homeowners in the area benefiting from this project.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 13, 16

-Article 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 5

-Section 02

-Subsection 20, 22