SUPPLEMENTAL DISCLOSURE WITH RESPECT TO CASH FLOWS (Narrative) (Details)	12 Months Ended
Sep. 30, 2021 shares
SUPPLEMENTAL DISCLOSURE WITH RESPECT TO CASH FLOWS
Number of shares issued upon cashless exercise of pre-funded warrants	81,303
Pre-funded warrants exercised	94,723

Number of common shares issued upon cashless exercise of pre-funded warrants

No definition available.

Name:	epix_StockIssuedDuringPeriodValuePreFundedWarrantsExercised
Namespace Prefix:	epix_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration