Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (USD $)	12 Months Ended
Dec. 31, 2014
Statement Of Stockholders Equity [Abstract]
Initial public offering of common stock, per share	$ 12.00us-gaap_EquityIssuancePerShareAmount
Offering costs	$ 3,859,052evok_OfferingCost

Amount per share or per unit assigned to the consideration received of equity securities issued for development stage entities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 915

-SubTopic 215

-Section 45

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6472370&loc=d3e38297-110927

Name:	us-gaap_EquityIssuancePerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration