Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details)	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015
Reclassifications Out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Reclassifications Out of Accumulated Other Comprehensive Income	not material	not material

Statement of whether reclassifications out of accumulated other comprehensive income (loss) were material for the period presented.

No definition available.

Name:	ale_ReclassificationsOutofAccumulatedOtherComprehensiveIncomeLossMateriality
Namespace Prefix:	ale_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration