Significant Accounting Polices - Additional Information (Details) - USD ($)			3 Months Ended		6 Months Ended
	Mar. 19, 2021	Jan. 25, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Schedule Of Significant Accounting Policies [Line Items]
Upfront nonrefundable payment		$ 1,000,000.0
Loan in principal amount		$ 4,000,000.0
Issuance and bore interest rate		6.00%
Reimbursement payment	$ 14,000,000.0
Collaboration agreement amount	25,000,000.0
Development payments	10,000,000.0
Deferred collaboration funding, short-term			$ 22,191,292		$ 22,191,292
Material accruals for preclinical or clinical study expense				$ 0		$ 0
Income tax expense (benefit)			$ 0	$ 0	$ 0	$ 0
Accounting Standards Update [Extensible List]					acer:AccountingStandardsUpdate202006Member
Change in accounting principle, accounting standards update, adopted			true		true
Change in accounting principle, accounting standards update, adoption date			Mar. 31, 2021		Mar. 31, 2021
Change in accounting principle, accounting standards update, immaterial effect			true		true
Accounts Payable and Accrued Expenses
Schedule Of Significant Accounting Policies [Line Items]
Preclinical or clinical study expense			$ 400,000		$ 400,000
Cash and Cash Equivalents
Schedule Of Significant Accounting Policies [Line Items]
Investments in money market funds			21,600,000		21,600,000		$ 5,300,000
Performance Obligations
Schedule Of Significant Accounting Policies [Line Items]
Deferred collaboration funding, short-term			22,200,000		22,200,000
Deferred collaboration funding cash received			25,000,000.0		25,000,000.0
Revenue recognized					900,000
Offset to research and development expenses					1,300,000
Offset to general and administrative expenses					600,000
Relief
Schedule Of Significant Accounting Policies [Line Items]
Non-cash reduction recognized in secured loan					4,000,000.0
Collaboration Agreement | Relief
Schedule Of Significant Accounting Policies [Line Items]
Cash payment received	10,000,000.0	$ 10,000,000.0
Reimbursement payment	14,000,000.0	14,000,000.0
Repayment of outstanding balance of prior loan and interest	4,000,000.0	$ 4,000,000.0
Development and commercial launch costs	$ 20,000,000.0
Net profit split ratio based on territory	60.00%	60.00%
Percentage of royalty net sales received	15.00%
Milestone payment to be received	$ 6,000,000.0	$ 6,000,000.0
Percentage of development and commercialization services	60.00%
Percentage of payment net profit territory	60.00%
Upfront non-refundable payment received		1,000,000.0
Collaboration Agreement | Relief | First Development Payment
Schedule Of Significant Accounting Policies [Line Items]
Cash payment received			10,000,000.0
Development payments subject new drug application			$ 10,000,000.0
Collaboration Agreement | Relief | Second Development Payment
Schedule Of Significant Accounting Policies [Line Items]
Development payments subject new drug application	$ 10,000,000.0	$ 10,000,000.0			$ 10,000,000.0
Collaboration And License Agreement
Schedule Of Significant Accounting Policies [Line Items]
Upfront non-refundable payment received	$ 1,000,000.0