Convertible Promissory Notes - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended	119 Months Ended	1 Months Ended					1 Months Ended			12 Months Ended	1 Months Ended
	Jul. 25, 2012	Dec. 31, 2012	Dec. 31, 2012	Jul. 25, 2012 Minimum	Feb. 28, 2013 Conversion of notes to preferred stock then to common stock	Jan. 23, 2013 Subsequent Event	Jan. 29, 2013 Subsequent Event	Jan. 28, 2013 Subsequent Event	Jul. 25, 2012 Conversion of Notes into Series A Preferred Stock	Jul. 25, 2012 Conversion of Notes into Series A Preferred Stock To partially fund, or an option to partner with Opexa	Jul. 25, 2012 Conversion of Notes into Series A Preferred Stock Additional capital from any partner, potential partner or any other source	Dec. 31, 2012 Warrant Liability	Jul. 25, 2012 Conversion of Series A Convertible Preferred Stock into common stock	Jul. 25, 2012 Related Party Transactions	Dec. 31, 2012 Related Party Transactions Warrant Liability
Debt Instrument [Line Items]
Convertible secured promissory notes, principal amount	$ 4,085,000													$ 630,000
Debt Instrument, Maturity Date	Jul. 25, 2014
Debt instrument interest payment date description	Interest is payable semi-annually on June 30 and December 31 in either cash or registered shares of common stock, at Opexa's election.
Convertible debt instrument, effective interest rate	12.00%
Convertible debt, conversion price	$ 100.00
Milestone to elect to convert Notes into Series A convertible preferred stock, minimum										5,000,000	25,000,000
Minimum common stock price required for 20 consecutive trading days to elect to convert									$ 10.00				$ 16.00
Conversion of Notes to Series A convertible preferred stock, description									The Notes can be converted into Series A convertible preferred stock at the option of the investors at a price of $100.00 per share, subject to certain limitations and adjustments. Additionally, Opexa can elect to convert the Notes into Series A convertible preferred stock if (i) Opexa’s common stock closes at or above $10.00 per share for 20 consecutive trading days or (ii) Opexa achieves certain additional funding milestones to continue its clinical trial program. These milestones include (x) executing a strategic agreement with a partner or potential partner by which Opexa will receive a minimum of $5 million to partially fund, or an option to partner with Opexa for, its Phase II clinical trial for Tcelna in patients with SPMS and (y) receiving a minimum of $25 million in additional capital (including the Note offering proceeds) from any partner, potential partner or any other source.
Series A Convertible Preferred Stock, dividend rate	8.00%
Dividend payment description	The Series A convertible preferred stock accrues dividends at the rate of 8%per annum, which are cumulative and payable semi-annually on June 30 and December 31 in either cash or registered shares of common stock at Opexa's election.
Series A Convertible Preferred Stock, Liquidation Preference	$ 100.00
Conversion of preferred stock into common stock, price per share	$ 3.12
Debt Conversion, Description													Additionally, Opexa can elect to convert the Series A convertible preferred stock into common stock if the Company's common stock closes at or above $16.00 per share for 20 consecutive trading days.
Convertible notes, principal amount converted					900,000
Restricted cash		1,000,000	1,000,000				500,000	500,000
Debt instrument, beneficial conversion feature	1,497,634													230,969
Warrants issued	957,422
Warrants exercise price	$ 5.00			$ 2.56		$ 1.24	$ 1.21
Warrants term	5 years					5 years	5 years
Warrant excercise terms subject to antidilution adjustment description	As a result of the antidilution adjustment, the number of warrant shares for which the Series I warrant is exercisable was subject to an aggregate increase to 1,436,121 shares of Opexa’s common stock at an adjusted exercise price of $2.56 per share, subject to certain limitations and adjustments. Opexa can redeem the warrants at $0.01 per share if its common stock closes at or above $10.00 per share for 20 consecutive trading days. As a result, Opexa accounted for these reset provisions in accordance with Accounting Standards Codification (“ASC”) ASC 815-40, which requires Opexa to record the warrants as a derivative liability at the grant date and to record changes in fair value relating to the warrants at each subsequent balance sheet date.
Warrant redemption per share description	Opexa can redeem the warrants at $0.01 per share if its common stock closes at or above $10.00 per share for 20 consecutive trading days.					The Company can redeem the warrants at $0.01 per share if the Company’s common stock closes at or above $10.00 per share for 20 consecutive trading days.	The Company can redeem the warrants at $0.01 per underlying share of common stock if the common stock closes at or above $10.00 per share for 20 consecutive trading days.
Discount on warrant	2,314,635	2,314,635	5,974,372
Amortized debt discount												104,032			16,044
Gain (loss) on derivative instruments		552,978	1,941,826									552,978
Convertible debt, unamortized discount		$ 3,708,237	$ 3,708,237											$ 587,939