XML 84 R71.htm IDEA: XBRL DOCUMENT v3.10.0.1

Commitments, Guarantees and Contingencies - Legal Proceedings (Details) - U.S. Water Services [Member] - U.S. Water Services Patent Defense Litigation [Member] $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Legal Proceedings [Line Items]
Patents Infringed	2
Addition to Intangible Assets for Patent Defense Costs	$ 2.5

X

- Definition

Finite-Lived Intangible Assets Addition for Patent Defense Costs

+ References

No definition available.

+ Details

Name:	ale_FiniteLivedIntangibleAssetsAdditionforPatentDefenseCosts
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

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

X

- Definition

Number of entity's patents that another entity has allegedly infringed.

+ References

No definition available.

+ Details

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

X

- Details

Name:	dei_LegalEntityAxis=ale_U.S.WaterServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_LitigationCaseAxis=ale_U.S.WaterServicesPatentDefenseLitigationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: