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Common Shares and Stock-Based Compensation - Summary of Incremental Compensation Expense and Capital in Excess of Par Value (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Feb. 28, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Compensation expense $ 10,601am_PostMergerIncrementalCompensationExpense
Capital in excess of par value (13,721)am_AdjustmentsToAdditionalPaidInCapitalSettlementModificationCancellationOfShareBasedCompensationAwards
Settlement Of Stock Options [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Compensation expense 3,226am_PostMergerIncrementalCompensationExpense
/ us-gaap_AwardTypeAxis
= am_SettlementOfStockOptionsMember
Capital in excess of par value (3,933)am_AdjustmentsToAdditionalPaidInCapitalSettlementModificationCancellationOfShareBasedCompensationAwards
/ us-gaap_AwardTypeAxis
= am_SettlementOfStockOptionsMember
Modification And Settlement Of Non Executive Directors Awards [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Compensation expense 512am_PostMergerIncrementalCompensationExpense
/ us-gaap_AwardTypeAxis
= am_ModificationAndSettlementOfNonExecutiveDirectorsAwardsMember
Capital in excess of par value (371)am_AdjustmentsToAdditionalPaidInCapitalSettlementModificationCancellationOfShareBasedCompensationAwards
/ us-gaap_AwardTypeAxis
= am_ModificationAndSettlementOfNonExecutiveDirectorsAwardsMember
Net Tax Deficiency From Settlement And Cancellation Of Stock-Based Awards [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Capital in excess of par value (6,885)am_AdjustmentsToAdditionalPaidInCapitalSettlementModificationCancellationOfShareBasedCompensationAwards
/ us-gaap_AwardTypeAxis
= am_NetTaxDeficiencyFromSettlementOfStockBasedAwardsMember
Conversion Of Performance Share And Restricted Stock Awards To Cash Based Liability Awards [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Compensation expense 2,897am_PostMergerIncrementalCompensationExpense
/ us-gaap_AwardTypeAxis
= am_ConversionOfPerformanceShareAndRestrictedStockAwardsToCashBasedLiabilityAwardsMember
Capital in excess of par value (6,498)am_AdjustmentsToAdditionalPaidInCapitalSettlementModificationCancellationOfShareBasedCompensationAwards
/ us-gaap_AwardTypeAxis
= am_ConversionOfPerformanceShareAndRestrictedStockAwardsToCashBasedLiabilityAwardsMember
Cancellation Of Family Shareholders Performance Share And Restricted Stock Awards [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Compensation expense 3,966am_PostMergerIncrementalCompensationExpense
/ us-gaap_AwardTypeAxis
= am_CancellationOfFamilyShareholdersPerformanceShareAndRestrictedStockAwardsMember
Capital in excess of par value $ 3,966am_AdjustmentsToAdditionalPaidInCapitalSettlementModificationCancellationOfShareBasedCompensationAwards
/ us-gaap_AwardTypeAxis
= am_CancellationOfFamilyShareholdersPerformanceShareAndRestrictedStockAwardsMember