Plan of Conversion - Additional Information (Detail) $ / shares in Units, $ in Millions	9 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares
Restructuring Cost and Reserve [Line Items]
Conversion stock offering completion date	Apr. 20, 2017
Gross proceeds from offering	$ 178.3
Converted shares | shares	17,826,408
Expenses related to offering	$ 3.6
Net proceeds from offering	174.7
Amount retained from net proceeds of the offering prior to the contribution	$ 87.3
PCSB Bank Employee Stock Ownership Plan [Member]
Restructuring Cost and Reserve [Line Items]
Common stock shares contributed to affiliate | shares	1,453,209
Stock price | $ / shares	$ 10.00
ESOP borrowing	$ 14.5
PCSB Community Foundation [Member]
Restructuring Cost and Reserve [Line Items]
Contributions in shares | shares	338,702
Contributions in cash	$ 1.6