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STOCK-BASED COMPENSATION - Additional Information (Detail) (USD $)
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3 Months Ended |
6 Months Ended |
1 Months Ended |
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Mar. 31, 2015
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Mar. 31, 2014
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Mar. 31, 2015
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Mar. 31, 2014
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Oct. 02, 2014
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Sep. 30, 2014
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Jun. 18, 2013
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Increase In Aggregate Number Of Shares |
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3,000,000arth_IncreaseInAggregateNumberOfShares
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| Share-based compensation arrangement by share-based payment award, options, outstanding, weighted average remaining contractual term |
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5 years 4 months 28 days
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| Share-based compensation arrangements by share-based payment award, options, grants in period, weighted average exercise price |
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$ 0.19us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
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| Share-based compensation arrangement by share-based payment award, fair value assumptions, expected volatility rate, minimum |
76.60%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum
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| Share-based compensation arrangement by share-based payment award, fair value assumptions, expected volatility rate, maximum |
119.40%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 |
957,544us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
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957,544us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
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| Allocated share-based compensation expense |
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$ 372,000us-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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300,000,000us-gaap_CommonStockSharesAuthorized
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| Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross |
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2,987,500us-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 |
153,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
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263,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
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274,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
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349,000us-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 |
178,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
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109,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
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335,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
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154,000us-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 arrangements by share-based payment award, options, grants in period, weighted average exercise price |
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$ 0.22us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
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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 arrangements by share-based payment award, options, grants in period, weighted average exercise price |
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$ 0.17us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
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| Share-based compensation arrangement by share-based payment award, fair value assumptions, expected term |
1 year
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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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| Allocated share-based compensation expense |
331,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= arth_EmployeesAndDirectorsMember
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609,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= arth_EmployeesAndDirectorsMember
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| Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross |
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7,254,212us-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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| Allocated share-based compensation expense |
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503,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= arth_ConsultantsMember
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| Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross |
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4,602,500us-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 |
0.20us-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 |
0.19us-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 |
696,647us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
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$ 696,647us-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 |
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1 year 10 months 6 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 | 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 |
1,950,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= arth_EmployeesAndDirectorsMember
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1,950,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= arth_EmployeesAndDirectorsMember
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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 |
3 years
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3 years
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| Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross |
500,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= arth_ConsultantsMember
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1,037,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= arth_ConsultantsMember
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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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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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