XML 122 R49.htm IDEA: XBRL DOCUMENT v2.4.1.9
Operations and Significant Accounting Policies - Concentraion of Credit Risk (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Customer Information [Line Items]      
Major Customer, Percent of Consolidated Revenue 10.80%us-gaap_ConcentrationRiskPercentage1 12.00%us-gaap_ConcentrationRiskPercentage1 12.30%us-gaap_ConcentrationRiskPercentage1
Large Power Customer [Member]      
Customer Information [Line Items]      
Number of Customers 10ale_NumberOfCustomers
/ ale_CustomerTypeAxis
= ale_LargePowerCustomerMember		    
Large Power Customers, Accounts Receivable 14.7us-gaap_AccountsReceivableGross
/ ale_CustomerTypeAxis
= ale_LargePowerCustomerMember		 14.2us-gaap_AccountsReceivableGross
/ ale_CustomerTypeAxis
= ale_LargePowerCustomerMember