Convertible Secured Promissory Notes - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended	9 Months Ended	116 Months Ended	1 Months Ended					1 Months Ended
	Jul. 25, 2012	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2012	Jul. 25, 2012 Warrant redemption per share at the option of the company	Jul. 25, 2012 Minimum	Jul. 25, 2012 Related Party Transactions	Sep. 30, 2012 Related Party Transactions	Dec. 31, 2011 Related Party Transactions	Jul. 25, 2012 Conversion of Series A Convertible Preferred Stock into common stock	Jul. 25, 2012 Conversion of Notes into Series A Preferred Stock	Jul. 25, 2012 Product Financing Arrangement Partial fund Minimum	Jul. 25, 2012 Product Financing Arrangement Additional capital Minimum
Debt Instrument [Line Items]
Convertible secured promissory notes issued	$ 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
Convertible secured promissory notes, conversion description					Opexa can redeem the warrants at $0.01 per share if its common stock closes at or above $2.50 per share for 20 consecutive trading days. In the event Opexa issues shares of common stock or common stock equivalents at a price less than the then current warrant exercise price, then the warrant exercise price will be reduced to the price at which Opexa issues such shares, subject to a warrant exercise floor price of $0.64 per share. If an adjustment to the warrant exercise price would otherwise go below the warrant exercise price floor, but for the floor limit, the number of warrant shares for which the warrant is exercisable may be increased by a factor equal to the warrant exercise price floor dividend by the lower price, subject to an aggregate increase cap of 50% of the original number of warrant shares.					Additionally, Opexa can elect to convert the Series A convertible preferred stock into common stock if Opexa’s common stock closes at or above $4.00 per share for 20 consecutive trading days. If, as of December 31, 2012, Opexa has not entered into a strategic agreement with a partner or potential partner pursuant to which Opexa has or will receive at least $5 million in funding for use toward the clinical development of Tcelna or in return for granting a license, other rights, or an option to license or otherwise acquire rights with respect to Tcelna, the then applicable Series A convertible preferred stock conversion price will be adjusted in the event of the closing of the first down-round financing following July 25, 2012 for the issuance of common stock or common stock equivalents, to the price per share at which Opexa sells securities in such financing, subject to a floor of $0.780625.	Additionally, Opexa can elect to convert the Notes into Series A convertible preferred stock if (i) Opexa’s common stock closes at or above $2.50 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.
Minimum common stock price required for 20 consecutive trading days to elect to convert										$ 4.00	$ 2.50
Milestone to receive under agreement												5,000,000	25,000,000
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	$ 0.80
Restricted cash		1,000,000	1,000,000	1,000,000
Debt Instrument, Beneficial Conversion Feature	1,497,634						230,969
Warrants issued	3,829,689
Warrants exercise price	$ 1.25					$ 0.64
Warrants term	5 years
Discount on warrant	2,314,635		2,314,635	5,974,372
Debt Instrument, Beneficial Conversion Feature	1,497,634		1,497,634	3,303,153
Amortized debt discount		34,600	34,600	6,787,298
Gain (loss) on derivative instruments		(136,889)	(136,889)	1,251,959
Convertible debt, unamortized discount		$ 3,777,668	$ 3,777,668	$ 3,777,668				$ 582,602	$ 0