Fair Value - Summary of Additional Quantitative Information about Assets Measured at Fair Value on Nonrecurring Basis (Detail) - Fair Value, Measurements, Nonrecurring [Member] - Level III [Member] $ in Thousands	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Estimate	$ 16,983	$ 8,128
Servicing Asset Valuation Technique Extensible List	essa:AppraisalOfCollateralMember	essa:AppraisalOfCollateralMember
Servicing Asset, Measurement Input [Extensible List]	essa:AppraisalAdjustmentsMember	essa:AppraisalAdjustmentsMember
Fair value input appraisal adjustments	0.205	0.203
Foreclosed Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Estimate	$ 269	$ 240
Servicing Asset Valuation Technique Extensible List	essa:AppraisalOfCollateralMember	essa:AppraisalOfCollateralMember
Servicing Asset, Measurement Input [Extensible List]	essa:AppraisalAdjustmentsMember	essa:AppraisalAdjustmentsMember
Fair value input appraisal adjustments	0.257	0.266
Minimum [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value input appraisal adjustments	0.00	0.00
Minimum [Member] | Foreclosed Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value input appraisal adjustments	0.20	0.20
Maximum [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value input appraisal adjustments	0.35	0.35
Maximum [Member] | Foreclosed Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value input appraisal adjustments	0.35	0.35