Fair Value of Financial Instruments - Summary of Quantitative Information about Level 3 Fair Value Measurements for Selected Financial Instruments Measured at Fair Value on Non-recurring Basis (Detail) $ in Thousands	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)
Minimum [Member] | Measurement Input, Discount Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range or Rate Used	0.10
Maximum [Member] | Measurement Input, Discount Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range or Rate Used	0.20
Measured on a Non-Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 425	$ 1,417
Measured on a Non-Recurring Basis [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	425	1,417
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Residential [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	316	616
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Residential [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	316	616
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Residential [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Discount Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	316	616
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Commercial Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	101	141
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Commercial Loans [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	101	141
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Commercial Loans [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Discount Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	101	141
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Home Equity Lines Of Credit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	8	7
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Home Equity Lines Of Credit [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	8	7
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Home Equity Lines Of Credit [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Discount Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 8	$ 7
Range or Rate Used	0.063	0.063
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Minimum [Member] | Residential [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Discount Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range or Rate Used	0.054	0.054
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Minimum [Member] | Commercial Loans [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Discount Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range or Rate Used	0.068	0.060
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Maximum [Member] | Residential [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Discount Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range or Rate Used	0.063	0.063
Measured on a Non-Recurring Basis [Member] | Impaired Loans [Member] | Maximum [Member] | Commercial Loans [Member] | Level 3 [Member] | Valuation Technique, Discounted Cash Flow [Member] | Measurement Input, Discount Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range or Rate Used	0.075	0.070
Measured on a Non-Recurring Basis [Member] | Foreclosed Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		$ 653
Measured on a Non-Recurring Basis [Member] | Foreclosed Real Estate [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		$ 653
Debt Securities, Available-for-sale, Valuation Technique [Extensible List]		pcsb:ValuationTechniqueSalesComparisonMember
Debt Securities, Available-for-sale, Measurement Input [Extensible List]		us-gaap:MeasurementInputComparabilityAdjustmentMember
Measured on a Non-Recurring Basis [Member] | Foreclosed Real Estate [Member] | Minimum [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range or Rate Used		(0.080)
Measured on a Non-Recurring Basis [Member] | Foreclosed Real Estate [Member] | Maximum [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range or Rate Used		0.450