Related Party Transactions (Details) - Board of Directors Chairman [Member] - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Direct sublease agreement
Related Party Transactions
Expenses incurred under related party transactions	$ 254	$ 119	$ 66
Direct sublease agreement \| NST, LLC [Member]
Related Party Transactions
Expenses incurred under related party transactions	387	124	66
Services agreement \| NST, LLC [Member]
Related Party Transactions
Expenses incurred under related party transactions	569	507	467
Other revenue earned from related party transactions	(153)	(553)	(413)
Net expenses (revenues) from related party transactions	416	(46)	54
Amount due to related party	91	0
Payments to related party	325		54
Receipts from related party		(46)
Services agreement \| NST, LLC [Member] \| General and administrative expense.
Related Party Transactions
Expenses incurred under related party transactions	323	455	467
Other revenue earned from related party transactions	(56)	(294)	(158)
Net expenses (revenues) from related party transactions	267	161	309
Services agreement \| NST, LLC [Member] \| Research and development expense.
Related Party Transactions
Expenses incurred under related party transactions	246	52
Other revenue earned from related party transactions	(97)	(259)	(255)
Net expenses (revenues) from related party transactions	$ 149	$ (207)	$ (255)

The amount of payments to related party during the period.

No definition available.

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

- Definition

The amount of cash received from related party during the period.

+ References

No definition available.

+ Details

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

- Definition

Expenses, net of revenues, recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

No definition available.

+ Details

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

- Definition

Receivables to be collected from (obligations owed to) related parties, net as of the balance sheet date where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k)(1))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_RelatedPartyTransactionDueFromToRelatedParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

+ Details

Name:	us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects the sum of all other revenue and income realized from sales and other transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_RelatedPartyTransactionOtherRevenuesFromTransactionsWithRelatedParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_BoardOfDirectorsChairmanMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_RelatedPartyTransactionAxis=acrs_DirectSubleaseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CounterpartyNameAxis=acrs_NstLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_RelatedPartyTransactionAxis=acrs_ServicesAgreementMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_GeneralAndAdministrativeExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_ResearchAndDevelopmentExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: