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Valuation and Qualifying Accounts (Narrative) (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
May 13, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Receivables aging period 60 days    
Accounts receivable reserve period 90 days    
Allowance for doubtful accounts $ 2,853us-gaap_AllowanceForDoubtfulAccountsReceivable $ 2,738us-gaap_AllowanceForDoubtfulAccountsReceivable  
Reserves for sales discounts 15,999us-gaap_SalesDiscountsGoods 16,724us-gaap_SalesDiscountsGoods  
Inventory obsolescence reserves 7,601us-gaap_InventoryValuationReserves 8,596us-gaap_InventoryValuationReserves  
Inventory usage period 3 years    
Inventory reserve percentage 100.00%alg_InventoryReservePercentage    
Product warranty accrual period of expenses used in calculation 12 months    
Product warranty accrual period for sales used in calculation 12 months    
Warranty 5,913us-gaap_ProductWarrantyAccrualClassifiedCurrent 4,994us-gaap_ProductWarrantyAccrualClassifiedCurrent  
Specialized Industries LP      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Increase in warranty reserve from acquisition of Specialized     $ 1,006alg_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentLiabilitiesProductWarrantyAccrual
/ us-gaap_BusinessAcquisitionAxis
= alg_SpecializedIndustriesLPMember
Wholegood Units      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Product warranty period 1 year    
Parts      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Product warranty period 90 days    
Minimum      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Sales discount percentage of customers who qualify for each program that discount available 90.00%alg_SalesDiscountsPercentageOfCustomersThatTakeDiscount
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		    
Product warranty accrual lag period 90 days    
Maximum      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Sales discount percentage of customers who qualify for each program that discount available 95.00%alg_SalesDiscountsPercentageOfCustomersThatTakeDiscount
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		    
Product warranty accrual lag period 6 months