Quarterly report pursuant to Section 13 or 15(d)

STOCK-BASED COMPENSATION - Additional Information (Detail)

v2.4.1.9
STOCK-BASED COMPENSATION - Additional Information (Detail) (USD $)
3 Months Ended 6 Months Ended 1 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2015
Mar. 31, 2014
Oct. 02, 2014
Sep. 30, 2014
Jun. 18, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Increase In Aggregate Number Of Shares             3,000,000arth_IncreaseInAggregateNumberOfShares
Share-based compensation arrangement by share-based payment award, options, outstanding, weighted average remaining contractual term     5 years 4 months 28 days        
Share-based compensation arrangements by share-based payment award, options, grants in period, weighted average exercise price     $ 0.19us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice        
Share-based compensation arrangement by share-based payment award, fair value assumptions, expected volatility rate, minimum 76.60%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum            
Share-based compensation arrangement by share-based payment award, fair value assumptions, expected volatility rate, maximum 119.40%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum            
Share-based compensation arrangement by share-based payment award, fair value assumptions, risk free interest rate, minimum 0.25%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum            
Share-based compensation arrangement by share-based payment award, fair value assumptions, risk free interest rate, maximum 2.40%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum            
Share based compensation arrangement by share based payment award fair value assumptions expected forfeiture rate 0.00%arth_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedForfeitureRate            
Share-based compensation arrangement by share-based payment award, fair value assumptions, expected dividend rate 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate            
Share-based compensation arrangement by share-based payment award, number of shares available for grant 957,544us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant   957,544us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant        
Allocated share-based compensation expense   $ 372,000us-gaap_AllocatedShareBasedCompensationExpense          
Common Stock, Shares Authorized 300,000,000us-gaap_CommonStockSharesAuthorized   300,000,000us-gaap_CommonStockSharesAuthorized     300,000,000us-gaap_CommonStockSharesAuthorized  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross     2,987,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross        
Research and Development Expense              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Allocated share-based compensation expense 153,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
263,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
274,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
349,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_ResearchAndDevelopmentExpenseMember
     
General and Administrative Expense              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Allocated share-based compensation expense 178,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
109,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
335,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
154,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_GeneralAndAdministrativeExpenseMember
     
Maximum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
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
       
Share-based compensation arrangement by share-based payment award, fair value assumptions, expected term 10 years            
Minimum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
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
       
Share-based compensation arrangement by share-based payment award, fair value assumptions, expected term 1 year            
Employees And Directors              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Allocated share-based compensation expense 331,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= arth_EmployeesAndDirectorsMember
  609,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= arth_EmployeesAndDirectorsMember
       
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross     7,254,212us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_TitleOfIndividualAxis
= arth_EmployeesAndDirectorsMember
       
Consultants              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Allocated share-based compensation expense       503,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= arth_ConsultantsMember
     
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross     4,602,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_TitleOfIndividualAxis
= arth_ConsultantsMember
       
Employees | Maximum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
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
           
Employees | Minimum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
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
           
2013 Stock Incentive Plan              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, total 696,647us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
  $ 696,647us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
       
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition     1 year 10 months 6 days        
Common Stock, Shares Authorized         13,114,256us-gaap_CommonStockSharesAuthorized
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
  10,231,197us-gaap_CommonStockSharesAuthorized
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
Share-based compensation arrangement by share-based payment award, number of additional shares authorized         2,883,059us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
   
2013 Stock Incentive Plan | Employees And Directors              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
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
  1,950,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= arth_EmployeesAndDirectorsMember
       
2013 Stock Incentive Plan | Consultants              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based compensation arrangement by share-based payment award, award vesting period 3 years   3 years        
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
  1,037,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= arth_TwoThousandAndThirteenStockIncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= arth_ConsultantsMember
       
2013 Stock Incentive Plan | Consultants | Maximum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based compensation arrangement by share-based payment award, options, outstanding, weighted average remaining contractual term 10 years   10 years        
2013 Stock Incentive Plan | Consultants | Minimum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Share-based compensation arrangement by share-based payment award, options, outstanding, weighted average remaining contractual term 1 year