CHANGE IN ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Components of Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains on securities transactions	$ 0	$ 329
Income before taxes	5,704	86,548
Income taxes	(1,737)	(21,407)
Net income attributable to WSFS	3,804	65,082
Reclassification out of Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income attributable to WSFS	(151)	(393)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Amortization of defined benefit pension plan-related items:
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior service costs (credits)	(19)	(22)
Actuarial (gains) losses	(17)	1
Income before taxes	(36)	(21)
Income taxes	9	5
Net income attributable to WSFS	(27)	(16)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net unrealized gains on terminated cash flow hedges:
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net unrealized gains to income during the period	(52)	(146)
Income taxes	12	35
Net income attributable to WSFS	(40)	(111)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Realized Gains on Securities Transactions | Net change in investment securities available-for-sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains on securities transactions	0	(329)
Income taxes	0	79
Net income attributable to WSFS	0	(250)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Amortization of Net Unrealized Gains to Income During Period | Net change in investment securities available-for-sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net unrealized gains to income during the period	(111)	(21)
Income taxes	27	5
Net income attributable to WSFS	$ (84)	$ (16)