Parent Company Financial Information - Schedule of condensed statements of financial condition (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2019
ASSETS
Cash on deposit at the Bank	$ 11,102	$ 21,385
Investment in the Bank	157,620	56,755
Other assets	6,312	6,076
TOTAL ASSETS	822,408	736,452
LIABILITIES
Accrued and other liabilities	7,648	10,811
TOTAL LIABILITIES	605,482	640,087
Commitments and contingencies
STOCKHOLDERS' EQUITY
Preferred stock, $.01 par value, 50,000,000 shares authorized; no shares issued
Common Stock, $.01 par value, 150,000,000 shares authorized; 15,170,566 shares issued and outstanding as of June 30, 2021 and $.03 par value, 159,666,500 shares authorized; 15,208,410 shares issued and 14,628,530 shares outstanding as of June 30, 2020	152	467
Additional paid-in capital	168,349	42,932
Treasury Stock, 0 and 579,879 shares at cost at June 30, 2021 and June 30, 2020, respectively		(3,710)
Unearned common stock held by employee stock ownership plan	(10,004)
Retained earnings	58,493	56,600
Accumulated other comprehensive (loss) income	(64)	76
TOTAL WILLIAM PENN BANCORPORATION STOCKHOLDERS' EQUITY	216,926	96,365	$ 76,630
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	822,408	736,452
Parent Company
ASSETS
Cash on deposit at the Bank	57,995	2,861
Investment in the Bank	158,857	93,401
Other assets	103	103
TOTAL ASSETS	216,955	96,365
LIABILITIES
Accrued and other liabilities	29
TOTAL LIABILITIES	29
Commitments and contingencies
STOCKHOLDERS' EQUITY
Common Stock, $.01 par value, 150,000,000 shares authorized; 15,170,566 shares issued and outstanding as of June 30, 2021 and $.03 par value, 159,666,500 shares authorized; 15,208,410 shares issued and 14,628,530 shares outstanding as of June 30, 2020	152	467
Additional paid-in capital	168,349	42,932
Treasury Stock, 0 and 579,879 shares at cost at June 30, 2021 and June 30, 2020, respectively		(3,710)
Unearned common stock held by employee stock ownership plan	(10,004)
Retained earnings	58,493	56,600
Accumulated other comprehensive (loss) income	(64)	76
TOTAL WILLIAM PENN BANCORPORATION STOCKHOLDERS' EQUITY	216,926	96,365
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 216,955	$ 96,365