BORROWED FUNDS - Narrative (Details) - USD ($)					3 Months Ended		12 Months Ended
	Jan. 01, 2022	Jun. 15, 2021	Dec. 03, 2020	Jun. 13, 2016	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2005	Dec. 31, 2021
Repurchase Agreement Counterparty [Line Items]
Securities sold under agreements to repurchase					$ 0			$ 0
Stock in Federal Home Loan Bank (FHLB) of Pittsburgh at cost					8,804,000			6,073,000
Deferred issuance costs					148,000,000
Collateralized borrowings					33,600,000			24,500,000
FHLB advances
Repurchase Agreement Counterparty [Line Items]
Borrowed funds balance					0			0
Federal Reserve Bank of Philadelphia
Repurchase Agreement Counterparty [Line Items]
Loans pledged as collateral					255,600,000			282,100,000
Borrowed funds					$ 0	$ 0
4.50% Senior Unsecured Notes Mature on 2026
Repurchase Agreement Counterparty [Line Items]
Interest rate on unsecured debt percent				4.50%
Senior unsecured notes, percentage of principle amount to be redeemed percent		100.00%
LIBOR Rate
Repurchase Agreement Counterparty [Line Items]
Variable interest rate percentage					2.15%
LIBOR Rate | 4.50% Senior Unsecured Notes Mature on 2026
Repurchase Agreement Counterparty [Line Items]
Variable interest rate percentage				3.30%
WSFS Capital Trust III
Repurchase Agreement Counterparty [Line Items]
Aggregate principal amount of pooled floating rate securities							$ 67,000,000
WSFS Capital Trust III | LIBOR Rate
Repurchase Agreement Counterparty [Line Items]
Variable interest rate percentage							1.77%
Trusts
Repurchase Agreement Counterparty [Line Items]
Aggregate principal amount of pooled floating rate securities	$ 12,500,000
Trust common securities owned	774,000
Floating rate common securities issued	387,000
FHLB advances
Repurchase Agreement Counterparty [Line Items]
Stock in Federal Home Loan Bank (FHLB) of Pittsburgh at cost					$ 8,800,000			$ 6,100,000
Dividends from the FHLB					$ 100,000	$ 100,000
Junior Subordinated Debt
Repurchase Agreement Counterparty [Line Items]
Interest rate on unsecured debt percent					2.98%
Junior Subordinated Debt | Trusts
Repurchase Agreement Counterparty [Line Items]
Trust capital securities issued	11,600,000
Trust capital securities issued net	23,200,000
Senior Notes
Repurchase Agreement Counterparty [Line Items]
Debt instrument, face amount				$ 100,000,000
Senior Notes 2030
Repurchase Agreement Counterparty [Line Items]
Interest rate on unsecured debt percent			2.75%
Debt instrument, face amount			$ 150,000,000
Redemption price, percentage			100.00%
Senior Notes 2030 | LIBOR Rate
Repurchase Agreement Counterparty [Line Items]
Variable interest rate percentage			2.485%
Senior Notes 2025
Repurchase Agreement Counterparty [Line Items]
Debt instrument, face amount	$ 30,000,000
Interest-bearing, interest rate					3.57%
Carrying value of securities purchased under agreements					$ 30,000,000
Senior Notes 2025 | LIBOR Rate
Repurchase Agreement Counterparty [Line Items]
Variable interest rate percentage	3.068%
Senior Notes 2027
Repurchase Agreement Counterparty [Line Items]
Interest rate on unsecured debt percent	4.25%
Debt instrument, face amount	$ 70,000,000
Carrying value of securities purchased under agreements					$ 70,500,000
Senior Notes 2027 | LIBOR Rate
Repurchase Agreement Counterparty [Line Items]
Variable interest rate percentage	2.05%