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Employee Benefit Plans - Multiemployer Plan (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Multiemployer Plans [Line Items]    
Contribution by Entity $ 5.0us-gaap_MultiemployerPlanPeriodContributions $ 1.1us-gaap_MultiemployerPlanPeriodContributions
Operating Engineers    
Multiemployer Plans [Line Items]    
Pension Protection Act Zone Status Red  
Contribution by Entity 4.3us-gaap_MultiemployerPlanPeriodContributions
/ us-gaap_MultiemployerPlanNameAxis
= alex_OperatingEngineersMember		 1.0us-gaap_MultiemployerPlanPeriodContributions
/ us-gaap_MultiemployerPlanNameAxis
= alex_OperatingEngineersMember
Surcharge Imposed No  
Laborers National    
Multiemployer Plans [Line Items]    
Pension Protection Act Zone Status Red  
Contribution by Entity 0.1us-gaap_MultiemployerPlanPeriodContributions
/ us-gaap_MultiemployerPlanNameAxis
= alex_LaborersNationalMember		 0us-gaap_MultiemployerPlanPeriodContributions
/ us-gaap_MultiemployerPlanNameAxis
= alex_LaborersNationalMember
Surcharge Imposed No  
Hawaii Laborers    
Multiemployer Plans [Line Items]    
Pension Protection Act Zone Status Green  
Contribution by Entity 0.5us-gaap_MultiemployerPlanPeriodContributions
/ us-gaap_MultiemployerPlanNameAxis
= alex_HawaiiLaborersOneMember		 0.1us-gaap_MultiemployerPlanPeriodContributions
/ us-gaap_MultiemployerPlanNameAxis
= alex_HawaiiLaborersOneMember
Surcharge Imposed No  
Hawaii Laborers    
Multiemployer Plans [Line Items]    
Pension Protection Act Zone Status Green  
Contribution by Entity $ 0.1us-gaap_MultiemployerPlanPeriodContributions
/ us-gaap_MultiemployerPlanNameAxis
= alex_HawaiiLaborersTwoMember		 $ 0us-gaap_MultiemployerPlanPeriodContributions
/ us-gaap_MultiemployerPlanNameAxis
= alex_HawaiiLaborersTwoMember
Surcharge Imposed No