Nature of Operations and Basis of Presentation - Additional Information (Details) - USD ($)				3 Months Ended
	Apr. 30, 2020	Mar. 18, 2020	Sep. 19, 2017	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Organization Consolidation and Presentation of Financial Statement [Line Items]
Accumulated deficit				$ 81,199,219		$ 76,250,512
Cash and cash equivalents				7,007,260		$ 12,077,640
Net cash used in operating activities				$ 5,070,380	$ 9,750,919
Common stock, shares issued				10,101,034		10,095,176
Current liabilities				$ 1,780,436		$ 2,768,913
Merger of Private Acer with opexa therapeutics incorporation and 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
Merger and Reincorporation
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. Immediately following the reincorporation, the holding company structure was eliminated by merging wholly-owned subsidiary Private Acer with and into the Company. The Company was the surviving corporation in connection with the subsidiary merger.
Date of reincorporation				May 15, 2018
Lincoln Park | Subsequent Event
Organization Consolidation and Presentation of Financial Statement [Line Items]
Purchase of common stock	$ 15,000,000
Maximum | Lincoln Park | Subsequent Event
Organization Consolidation and Presentation of Financial Statement [Line Items]
Purchase of common stock	$ 15,000,000
At-the-Market Facility
Organization Consolidation and Presentation of Financial Statement [Line Items]
Common stock, shares issued				0
At-the-Market Facility | Maximum
Organization Consolidation and Presentation of Financial Statement [Line Items]
Aggregate offering price of common stock		$ 50,000,000