Nature of Operations and Basis of Presentation - Additional Information (Details)		3 Months Ended
	Sep. 19, 2017	Mar. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares	May 15, 2018 $ / shares	May 14, 2018 $ / shares	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Organization Consolidation and Presentation of Financial Statement [Line Items]
Cash and cash equivalents | $		$ 31,831,427	$ 41,671,284			$ 12,368,625	$ 15,644,355
Common stock, par value		$ 0.0001	$ 0.0001		$ 0.01
Merger of Private Acer with Opexa Merger Sub Incorporation
Organization Consolidation and Presentation of Financial Statement [Line Items]
Business combination date of completion	Sep. 19, 2017
Business combination date of agreement	Jun. 30, 2017
Reverse stock split ratio	0.09656678989
Delaware Reincorporation and Subsidiary Merger
Organization Consolidation and Presentation of Financial Statement [Line Items]
Merger incorporation description		On May 15, 2018, the Company changed its state of incorporation from the State of Texas to the State of Delaware pursuant to a plan of conversion, dated May 15, 2018. As a result of this reincorporation, the par value of the Company’s common stock was reduced to $0.0001 from $0.01. Immediately following the Reincorporation, we eliminated our holding company structure by merging our wholly-owned subsidiary Private Acer with and into the Company (the “Subsidiary Merger”). The Company was the surviving corporation in connection with the Subsidiary Merger.
Date Of Reincorporation		May 15, 2018
Common stock, par value				$ 0.0001