CHANGE IN ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Components of Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains on securities transactions	$ 0	$ 2	$ 0	$ 331
Income taxes	(25,767)	(17,516)	(49,929)	(70,610)
Amortization of net unrealized losses (gains) to income during the period	176,831	104,491	469,004	325,425
Income before taxes	99,111	71,968	188,142	285,814
Net income attributable to WSFS	73,382	54,406	137,926	215,155
Reclassification out of Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income attributable to WSFS	5,899	(158)	5,709	(708)
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	9	5	26	15
Prior service costs (credits)	(19)	(22)	(57)	(66)
Actuarial (gains) losses	(17)	2	(51)	5
Income before taxes	(36)	(20)	(108)	(61)
Net income attributable to WSFS	(27)	(15)	(82)	(46)
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]
Income taxes	13	36	38	106
Amortization of net unrealized gains to income during the period	(54)	(149)	(158)	(442)
Net income attributable to WSFS	(41)	(113)	(120)	(336)
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]
Income taxes	(1,884)	9	(1,866)	23
Amortization of net unrealized losses (gains) to income during the period	7,851	(37)	7,777	(97)
Net income attributable to WSFS	5,967	(28)	5,911	(74)
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	(2)	0	(331)
Income taxes	0	0	0	79
Net income attributable to WSFS	$ 0	$ (2)	$ 0	$ (252)