CHANGE IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains on securities transactions	$ 0	$ 0	$ 331
Income taxes	(96,245)	(77,961)	(86,095)
Income before taxes	365,270	300,609	357,700
Reclassification out of Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income attributable to WSFS	16,609	10,822	(796)
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]
Income taxes	83	35	20
Prior service (credits) costs	(76)	(76)	(85)
Actuarial gains	(271)	(68)	0
Income before taxes	(347)	(144)	(85)
Net income attributable to WSFS	(264)	(109)	(65)
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 losses (gains) to income during the period	(141)	(211)	(497)
Income taxes	34	51	119
Net income attributable to WSFS	(107)	(160)	(378)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Securities available-for-sale: | Net change in investment securities available for sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains on securities transactions	0	0	(331)
Income taxes	0	0	79
Net income attributable to WSFS	0	0	(252)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net unrealized holding losses (gains) on securities transferred between available-for-sale and held-to-maturity: | Net change in investment securities available for sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net unrealized losses (gains) to income during the period	22,343	14,593	(133)
Income taxes	(5,363)	(3,502)	32
Net income attributable to WSFS	$ 16,980	$ 11,091	$ (101)