Nature of Operations and Basis of Presentation - Additional Information (Details)			12 Months Ended
	Sep. 19, 2017 $ / shares shares	Sep. 18, 2017 USD ($) $ / shares	Dec. 31, 2017 USD ($) Patient shares	Dec. 31, 2016 shares
Organization Consolidation and Presentation of Financial Statement [Line Items]
Number of patients unapproved | Patient			7,000
Common stock, shares outstanding | shares	6,500,000		7,497,433	2,450,000
Aggregate common stock issued and sold prior to merger			$ 21,506,842
Shares issued price per share | $ / shares	$ 9.47
Private Acer
Organization Consolidation and Presentation of Financial Statement [Line Items]
Shares issued in exchange of common stock upon merger	1.00%
Percentage of outstanding common stock owned by acquirer's shareholders	89.00%
Percentage of outstanding common stock owned by registrant's shareholders	11.00%
Aggregate common stock issued and sold prior to merger		$ 15,700,000
Shares issued price per share | $ / shares		$ 9.47
Private Acer | Convertible Promissory Notes
Organization Consolidation and Presentation of Financial Statement [Line Items]
Debt conversion, outstanding principal and accrued interest		$ 5,700,000
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