Consolidated Statements of Changes In Stockholders' Equity (Parenthetical) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2013
Share purchase agreement, value	$ 1.5

Shares To Be Issued Under Securities Purchase Agreement Value

No definition available.

Name:	opxa_SharesToBeIssuedUnderSecuritiesPurchaseAgreementValue
Namespace Prefix:	opxa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration