Document and Entity Information - shares	6 Months Ended
	Mar. 31, 2021	May 05, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
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	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		10,667,401
Entity File Number	001-33384
Entity Tax Identification Number	20-8023072
Entity Address, Address Line One	200 Palmer Street
Entity Address, City or Town	Stroudsburg
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	18360
City Area Code	570
Local Phone Number	421-0531
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	PA
Document Quarterly Report	true
Document Transition Report	false