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Stock-Based Compensation - Additional Information (Detail) (USD $)
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3 Months Ended |
1 Months Ended |
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Dec. 31, 2014
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Dec. 31, 2013
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Oct. 02, 2014
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Sep. 30, 2014
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Jun. 18, 2013
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Increase In Aggregate Number Of Shares |
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3,000,000arth_IncreaseInAggregateNumberOfShares
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| Percentage of outstanding number of shares |
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4.00%arth_PercentageOfOutstandingNumberOfShares
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| Share-based compensation arrangement by share-based payment award, options, outstanding, weighted average remaining contractual term |
5 years 5 months 8 days
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| Share-based compensation arrangements by share-based payment award, options, grants in period, weighted average exercise price |
$ 0.17us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
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| Share-based compensation arrangement by share-based payment award, fair value assumptions, expected volatility rate, minimum |
77.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum
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| Share-based compensation arrangement by share-based payment award, fair value assumptions, expected volatility rate, maximum |
119.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum
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| Share-based compensation arrangement by share-based payment award, fair value assumptions, risk free interest rate, minimum |
0.25%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum
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| Share-based compensation arrangement by share-based payment award, fair value assumptions, risk free interest rate, maximum |
2.40%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum
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| Share based compensation arrangement by share based payment award fair value assumptions expected forfeiture rate |
0.00%arth_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedForfeitureRate
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| Share-based compensation arrangement by share-based payment award, fair value assumptions, expected dividend rate |
0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
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| Share-based compensation arrangement by share-based payment award, number of shares available for grant |
3,707,544us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
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| Allocated share-based compensation expense |
$ 278,000us-gaap_AllocatedShareBasedCompensationExpense
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$ 132,000us-gaap_AllocatedShareBasedCompensationExpense
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| Common Stock, Shares Authorized |
300,000,000us-gaap_CommonStockSharesAuthorized
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300,000,000us-gaap_CommonStockSharesAuthorized
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| Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross |
537,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
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| Research and Development Expense |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Allocated share-based compensation expense |
121,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
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86,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
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| General and Administrative Expense |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Allocated share-based compensation expense |
157,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
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46,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
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| Maximum |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Share-based compensation arrangement by share-based payment award, fair value assumptions, expected term |
10 years
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| Minimum |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Share-based compensation arrangement by share-based payment award, fair value assumptions, expected term |
9 months 18 days
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| Employees And Directors |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross |
4,102,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_TitleOfIndividualAxis
= arth_EmployeesAndDirectorsMember
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| Consultants |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross |
5,304,212us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_TitleOfIndividualAxis
= arth_ConsultantsMember
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| Employees | Maximum |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Share-based compensation arrangements by share-based payment award, options, grants in period, weighted average exercise price |
$ 0.22us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_TitleOfIndividualAxis
= arth_EmployeesMember
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| Employees | Minimum |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Share-based compensation arrangements by share-based payment award, options, grants in period, weighted average exercise price |
$ 0.17us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_TitleOfIndividualAxis
= arth_EmployeesMember
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| 2013 Stock Incentive Plan |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, total |
$ 801,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
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| Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition |
1 year 9 months 25 days
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| Common Stock, Shares Authorized |
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13,114,256us-gaap_CommonStockSharesAuthorized
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
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10,231,197us-gaap_CommonStockSharesAuthorized
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
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| Share-based compensation arrangement by share-based payment award, number of additional shares authorized |
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2,883,059us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
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| 2013 Stock Incentive Plan | Consultants |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Share-based compensation arrangement by share-based payment award, award vesting period |
4 years
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| 2013 Stock Incentive Plan | Consultants | Maximum |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Share-based compensation arrangement by share-based payment award, options, outstanding, weighted average remaining contractual term |
10 years
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| 2013 Stock Incentive Plan | Consultants | Minimum |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Share-based compensation arrangement by share-based payment award, options, outstanding, weighted average remaining contractual term |
1 year
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