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Investments - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Available-for-sale, investment securities held with maturity dates more than one year and less than two years	$ 44.2	$ 48.7

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- Definition

Available for sale securities debt maturities rolling year one through two.

+ References

No definition available.

+ Details

Name:	acad_AvailableForSaleSecuritiesDebtMaturitiesRollingYearOneThroughTwo
Namespace Prefix:	acad_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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- References

No definition available.

+ Details

Name:	us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration