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Severance Charges - Additional Information (Detail) | Sep. 30, 2017 USD ($) | Aug. 01, 2017 USD ($) SeniorExecutive
--- | --- | ---
Restructuring Cost and Reserve [Line Items] |  |
Number of terminated senior executives | SeniorExecutive |  | 1
Senior Executive [Member] |  |
Restructuring Cost and Reserve [Line Items] |  |
Severance payable | $ | $ 0 | $ 1,200,000

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- Definition Number of terminated senior executives. + References No definition available. + Details
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Namespace Prefix: | achv_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
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- Definition Liability for amount due employees, in addition to wages and any other money that employers owe employees, when their employment ends through a layoff or other termination. For example, a company may provide involuntarily terminated employees with a lump sum payment equal to one week's salary for every year of employment. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |