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Share-Based Compensation - Textual (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
12 Months Ended 0 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Apr. 12, 2006
Apr. 18, 2012
Apr. 09, 2009
Apr. 18, 2007
Dec. 31, 2007
Feb. 28, 2014
Stock Options and Stock Appreciation Rights                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Total intrinsic value of share-based payment award exercised $ 770ahs_ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisesInPeriodIntrinsicValue
/ us-gaap_AwardTypeAxis
= ahs_StockOptionsAndStockAppreciationRightsMember
$ 980ahs_ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisesInPeriodIntrinsicValue
/ us-gaap_AwardTypeAxis
= ahs_StockOptionsAndStockAppreciationRightsMember
$ 453ahs_ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisesInPeriodIntrinsicValue
/ us-gaap_AwardTypeAxis
= ahs_StockOptionsAndStockAppreciationRightsMember
           
Total intrinsic value of share-based payment award outstanding and exercisable 10,142ahs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOutstandingandExercisableTotalIntrinsicValue
/ us-gaap_AwardTypeAxis
= ahs_StockOptionsAndStockAppreciationRightsMember
5,146ahs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOutstandingandExercisableTotalIntrinsicValue
/ us-gaap_AwardTypeAxis
= ahs_StockOptionsAndStockAppreciationRightsMember
             
Restricted Stock Units (RSUs)                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Vesting period 3 years                
Unrecognized compensation cost, weighted average remaining period 1 year 9 months 18 days                
Total unrecognized compensation cost 7,742us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
               
Aggregate instrinsic value $ 30,876us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstanding
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
$ 24,070us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstanding
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
             
Stock Option Plan                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Shares of common stock transferred between plans       371,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherShareIncreaseDecrease
/ us-gaap_PlanNameAxis
= ahs_StockOptionPlanMember
         
Stock Option Plan | Stock Options                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Number of shares authorized for issuance 4,178,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= ahs_StockOptionPlanMember
               
Stock Option Plan | Stock Options | Vesting Period, Anniversary of Grant Date                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Vesting percentage 25.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= ahs_StockOptionPlanMember
/ us-gaap_VestingAxis
= ahs_VestingPeriodAnniversaryOfGrantDateMember
               
Number of vesting periods 4ahs_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRightsNumberOfPeriods
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= ahs_StockOptionPlanMember
/ us-gaap_VestingAxis
= ahs_VestingPeriodAnniversaryOfGrantDateMember
               
Stock Option Plan | Stock Options and Stock Appreciation Rights                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Equity awards reserved for future issuance 0us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
/ us-gaap_AwardTypeAxis
= ahs_StockOptionsAndStockAppreciationRightsMember
/ us-gaap_PlanNameAxis
= ahs_StockOptionPlanMember
               
Equity Plan | Stock Options and Stock Appreciation Rights                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Number of shares authorized for issuance               723,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_AwardTypeAxis
= ahs_StockOptionsAndStockAppreciationRightsMember
/ us-gaap_PlanNameAxis
= ahs_EquityPlanMember
 
Equity awards reserved for future issuance 2,421,000us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
/ us-gaap_AwardTypeAxis
= ahs_StockOptionsAndStockAppreciationRightsMember
/ us-gaap_PlanNameAxis
= ahs_EquityPlanMember
2,173,000us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
/ us-gaap_AwardTypeAxis
= ahs_StockOptionsAndStockAppreciationRightsMember
/ us-gaap_PlanNameAxis
= ahs_EquityPlanMember
             
Contractual life of stock options and SARs 10 years                
Additional number of shares authorized         2,400,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ us-gaap_AwardTypeAxis
= ahs_StockOptionsAndStockAppreciationRightsMember
/ us-gaap_PlanNameAxis
= ahs_EquityPlanMember
1,850,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ us-gaap_AwardTypeAxis
= ahs_StockOptionsAndStockAppreciationRightsMember
/ us-gaap_PlanNameAxis
= ahs_EquityPlanMember
3,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ us-gaap_AwardTypeAxis
= ahs_StockOptionsAndStockAppreciationRightsMember
/ us-gaap_PlanNameAxis
= ahs_EquityPlanMember
   
2014 Employee Inducement Plan                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Number of shares authorized for issuance                 200us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= ahs_TwoThousandFourteenEmployeeInducementPlanMember
Shares of common stock available for future grants 200us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= ahs_TwoThousandFourteenEmployeeInducementPlanMember