Document and Entity Information - shares	6 Months Ended
	Mar. 31, 2017	May 08, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q2
Trading Symbol	ESSA
Entity Registrant Name	ESSA Bancorp, Inc.
Entity Central Index Key	0001382230
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		11,586,202