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Shareholders' equity (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified | 3 Months Ended | 12 Months Ended | 15 Months Ended
--- | --- | --- | ---
Mar. 31, 2015 | Dec. 31, 2014 | Mar. 31, 2014 | Dec. 31, 2013 | Mar. 31, 2015
Aggregate intrinsic value |  |  |  |  |
Weighted average remaining life (years) |  | 8 years 9 months 18 days |  | 9 years 3 months 18 days |
Weighted average exercisable (years) | 7 years 9 months 18 days |  | 8 years 6 months |  |
Stock options |  |  |  |  |
Class of Stock |  |  |  |  |
Vesting period | 4 years |  | 4 years |  |
Expiration period | 10 years |  | 10 years |  |
Restricted stock units |  |  |  |  |
Class of Stock |  |  |  |  |
Vesting period |  |  |  |  | 4 years
Expiration period |  |  |  |  | 10 years
Stock Options |  |  |  |  |
Outstanding at beginning of the period (in shares) | 85,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  |  |  |
Granted (in shares) | 42,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  | 92,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  |
Exercised (in shares) | (21,250)us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  |  |  |
Forfeited (in shares) | (6,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  | (2,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  |
Outstanding at end of the period (in shares) | 99,750 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  | 90,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  | 99,750 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember
2012 Equity Incentive Plan | Stock options |  |  |  |  |
Stock Options |  |  |  |  |
Outstanding at beginning of the period (in shares) | 2,165,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 1,190,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 1,190,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember
Granted (in shares) | 553,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 970,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  |
Forfeited (in shares) | (110,500)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | (41,250)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  |
Outstanding at end of the period (in shares) | 2,608,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 2,118,750 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 2,608,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember
Exercisable at end of the period (in shares) | 597,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 160,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 597,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember
Weighted Average Exercise Price |  |  |  |  |
Outstanding at beginning of the period (in dollars per share) | 16.17 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 15.48 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 15.48 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember
Granted (in dollars per share) | 16.48 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 16.63 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  |
Forfeited (in dollars per share) | 16.57 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 16.18 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  |
Outstanding at end of the period (in dollars per share) | 16.22 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 15.99 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 16.22 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember
Exercisable at end of the period (in dollars per share) | 15.80 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 15.00 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 15.80 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember
Aggregate intrinsic value |  |  |  |  |
Weighted average remaining life (years) | 8 years 8 months 12 days |  | 9 years 4 months 24 days |  |
Aggregate intrinsic value | 1,064 us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1 / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember | 1,890 us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1 / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember | 1,532 us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1 / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember | 862 us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1 / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember | 1,064 us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1 / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember
Aggregate intrinsic value exercisable | 466 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 274 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  | 466 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember
2012 Equity Incentive Plan | Restricted stock units |  |  |  |  |
Class of Stock |  |  |  |  |
Stock options granted | 42,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember |  |  |  |
2012 Equity Incentive Plan | Class A common shares |  |  |  |  |
Class of Stock |  |  |  |  |
Stock options granted | 553,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember |  | 970,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod / us-gaap_PlanNameAxis = amh_TwoThousandTwelveEquityIncentivePlanMember / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember |  |

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