Related Party Transaction (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Direct sublease agreement
Related Party Transactions
Expenses incurred under related party transactions			$ 178	$ 86
Direct sublease agreement \| NST, LLC [Member]
Related Party Transactions
Expenses incurred under related party transactions	$ 64	$ 44	179	97
Services agreement
Related Party Transactions
Net expenses (revenues) from related party transactions	103	(27)	310	(18)
Services agreement \| General and administrative expense.
Related Party Transactions
Net expenses (revenues) from related party transactions	64	36	192	172
Services agreement \| Research and development expense.
Related Party Transactions
Net expenses (revenues) from related party transactions	39	(63)	118	(190)
Services agreement \| NST, LLC [Member]
Related Party Transactions
Expenses incurred under related party transactions	139	105	418	358
Other revenue earned from related party transactions	(36)	(132)	(108)	(376)
Payments to related party	88		263	13
Receipts from related party		(2)
Services agreement \| NST, LLC [Member] \| General and administrative expense.
Related Party Transactions
Expenses incurred under related party transactions	79	105	237	358
Other revenue earned from related party transactions	(15)	(69)	(45)	(186)
Services agreement \| NST, LLC [Member] \| Research and development expense.
Related Party Transactions
Expenses incurred under related party transactions	60		181
Other revenue earned from related party transactions	(21)	(63)	$ (63)	$ (190)
Director \| Direct sublease agreement
Related Party Transactions
Expenses incurred under related party transactions	$ 66	$ 34

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

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

+ 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 (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ 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_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:
Period Type:

- Details

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

- 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:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_DirectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: