Convertible Promissory Notes - Additional Information (Detail) (USD $)	1 Months Ended							12 Months Ended				131 Months Ended	1 Months Ended		1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended	1 Months Ended					1 Months Ended					12 Months Ended			1 Months Ended		12 Months Ended						12 Months Ended	1 Months Ended
	Dec. 23, 2013	Sep. 30, 2013	Sep. 24, 2013	Feb. 11, 2013	Jan. 23, 2013	Jan. 31, 2013	Jul. 25, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2010	Dec. 31, 2004	Dec. 31, 2013	Jul. 25, 2012 Minimum	Jul. 25, 2012 Maximum	Feb. 28, 2013 Common Stock	Dec. 31, 2013 Common Stock	Dec. 31, 2010 Common Stock	Dec. 31, 2004 Common Stock	Feb. 28, 2013 January 2013 Notes	Dec. 31, 2013 January 2013 Notes	Feb. 28, 2013 January 2013 Notes Common Stock	Sep. 24, 2013 Amendment	Sep. 23, 2013 Amendment	Sep. 23, 2013 Amendment Minimum	Sep. 23, 2013 Amendment Maximum	Sep. 24, 2013 Amendment Common Stock	Jul. 25, 2012 July 2012 Notes	Jul. 25, 2012 July 2012 Notes Conversion of Notes into Series A Preferred Stock	Jul. 25, 2012 July 2012 Notes Conversion of Notes into Series A Preferred Stock To partially fund, or an option to partner with Opexa	Jul. 25, 2012 July 2012 Notes Conversion of Notes into Series A Preferred Stock Additional capital from any partner, potential partner or any other source	Dec. 31, 2012 Warrant Liability	Dec. 31, 2013 Option and License Agreement	Feb. 04, 2013 Option and License Agreement	Jul. 25, 2012 Conversion of Series A Convertible Preferred Stock into common stock	Jul. 25, 2012 Related Party Transactions	Dec. 31, 2013 Related Party Transactions	Sep. 24, 2013 Related Party Transactions	Jan. 31, 2013 Related Party Transactions	Jul. 25, 2012 Related Party Transactions July 2012 Notes	Sep. 24, 2013 Related Party Transactions Warrant Liability	Dec. 31, 2012 Related Party Transactions Warrant Liability	Dec. 31, 2013 Related Party	Feb. 28, 2013 Convertible debt	Jan. 23, 2013 Convertible debt	Feb. 28, 2013 Convertible debt Common Stock	Jan. 23, 2013 Convertible debt Related Party
Debt Instrument [Line Items]
Convertible secured promissory notes, principal amount							$ 4,085,000																				$ 4,085,000								$ 630,000		$ 647,813	$ 100,000	$ 630,000
Debt Instrument, Maturity Date																											Jul. 25, 2014																	Jan. 23, 2014
Debt instrument interest payment date description																											Interest was 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%																	12.00%
Convertible debt, conversion price																						$ 1.91		$ 1.50	$ 2.25		$ 100.00													$ 1.91				$ 1.30
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 could 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 could elect to convert the Notes into Series A convertible preferred stock if (i) Opexa’s common stock closed at or above $10.00 per share for 20 consecutive trading days or (ii) Opexa achieved certain additional funding milestones to continue its clinical trial program. These milestones included (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 accrued 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
Common stock issuable upon conversion of convertible secured promissory notes into Series A preferred stock														1,308,236
Debt Conversion, Description																																		Additionally, Opexa could 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.
Restricted cash						500,000		0	1,000,000			0
Debt instrument, beneficial conversion feature						141,829	1,497,634	141,829																											230,969	21,820
Amortized debt discount									1,497,634																						104,032										16,044
Warrants issued							957,422
Warrants exercise price				$ 3.00	$ 1.24	$ 1.21	$ 5.00						$ 2.56
Warrants term				4 years	5 years	5 years	5 years
Warrant excercise terms subject to antidilution adjustment description							As a result of anti-dilution adjustments, the number of warrant shares for which the Series I warrants are exercisable increased to an aggregate increase of 1,436,121 shares of Opexa’s common stock at an adjusted exercise price of $2.56 per share, subject to further certain limitations and adjustments. As a result, Opexa accounted for these reset provisions in accordance with FASB 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 the Company's common stock closes at or above $10.00 per share for 20 consecutive trading days.	Opexa 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.	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.
Discount on warrant						195,969	2,314,635	195,969	2,314,635			6,170,341
Gain (loss) on derivative instruments									552,978			1,941,826																			552,978
Convertible debt, unamortized discount			2,432,681						3,708,237																										587,939
Convertible notes, principal amount converted																			100,000																								900,000
Common shares issued	4,738,000	900,000																																											288,229
Aggregate principal amount outstanding			756,141																				3,185,000
Conversion of convertible notes								4,275,053		1,380,091	248,370					20,799	6,900	7,594				3,275,053
Common shares issued, note conversion			1,714,697												365,263	2,079,960	690,045	15,187			77,034					1,714,697
Loss on extinguishment of debt			(2,518,912)					(2,518,912)				(906,472)
Accrued interest			98,053
Unamortized deferred financing cost			86,231						211,479
Gross proceed from the issuance of convertible note																																												650,000		100,000
Minimum receipt of proceeds from sale of equity securities and/or as payments from partners to pay any remaining balance of note payable																																												7,500,000
Number of business days to pay remaining convertible debts																																												5 days
Warrants issued					243,750	243,750
Gross proceeds from sales of common stock and warrants to purchase shares of common stock								3,250,000
Proceeds from up front cash payment																																5,000,000	5,000,000
Principal and interest paid								567,368																																		100,000
Amortization of debt discount to interest expense								$ 1,613,354	$ 104,032			$ 8,470,084								$ 337,798