This element represents the milestone expenses.

No definition available.

Name:	acrs_MilestoneExpenses
Namespace Prefix:	acrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Future payments that could be paid upon achievement of certain milestones per agreement.

+ References

No definition available.

+ Details

Name:	acrs_PotentialMilestonesPayable
Namespace Prefix:	acrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Future payments that could be received upon achievement of certain milestones per agreement.

+ References

No definition available.

+ Details

Name:	acrs_PotentialMilestonesReceivable
Namespace Prefix:	acrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The minimum period before expiration of the agreement, starting from agreement effective date.

+ References

No definition available.

+ Details

Name:	acrs_TermOfAgreementMinimum
Namespace Prefix:	acrs_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue from upfront payment received during the period.

+ References

No definition available.

+ Details

Name:	acrs_UpfrontPaymentRevenue
Namespace Prefix:	acrs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

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

- Definition

Amount of expense related to royalty payments under a contractual arrangement such as payment for mineral and drilling rights and use of technology or intellectual property.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.3)
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

+ Details

Name:	us-gaap_RoyaltyExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_TypeOfArrangementAxis=acrs_AssignmentAgreementAndFinderSServicesAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=acrs_AchievementOfSpecifiedCommercialMilestonesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=acrs_AchievementOfSpecifiedRegulatoryMilestonesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=acrs_FindersServicesAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=acrs_LicenseAndCollaborationAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=acrs_AchievementOfDevelopmentMilestonesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Agreements Related to Intellectual Property (Details) - USD ($) $ in Thousands		1 Months Ended			9 Months Ended
	Apr. 18, 2018	May 31, 2018	Apr. 30, 2017	Aug. 31, 2012	Sep. 30, 2018
Assignment Agreement and Finder's Services Agreement
Agreements Related to Intellectual Property
Term of agreement, minimum				15 years
Assignment Agreement and Finder's Services Agreement \| Achievement Of Specified Commercial Milestones
Agreements Related to Intellectual Property
Milestone Expenses		$ 1,500
Assignment Agreement and Finder's Services Agreement \| Achievement Of Specified Regulatory Milestones
Agreements Related to Intellectual Property
Milestone Expenses			$ 1,000
Finders Services Agreement \| Achievement Of Specified Commercial Milestones
Agreements Related to Intellectual Property
Potential Milestones Payable					$ 3,000
Aggregate royalty payments					82
License and collaboration agreement
Agreements Related to Intellectual Property
Upfront payment revenue					$ 1,000
Term of agreement, minimum	15 years
License and collaboration agreement \| Achievement Of Specified Commercial Milestones
Agreements Related to Intellectual Property
Potential Milestones Receivable	$ 1,750
License and collaboration agreement \| Achievement Of Development Milestones
Agreements Related to Intellectual Property
Potential Milestones Receivable	$ 1,000