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Other Assets - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2017
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract] |
Period of not utilizing deferred share issuance costs and prepaid amounts related to insurance | 12 months

X
- Definition Period of not utilizing deferred share issuance costs and prepaid amounts related to insurance. + References No definition available. + Details
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Namespace Prefix: | achv_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_DeferredCostsCapitalizedPrepaidAndOtherAssetsDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration