CHANGE IN ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Components of Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains on securities transactions	$ 0	$ 0	$ 0	$ 329
Income taxes	(22,425)	(31,687)	(24,162)	(53,094)
Income before taxes	83,327	127,298	89,031	213,846
Net income attributable to WSFS	60,740	95,667	64,544	160,749
Reclassification out of Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income attributable to WSFS	(39)	(155)	(191)	(548)
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	17	10
Prior service costs (credits)	(19)	(22)	(38)	(44)
Actuarial (gains) losses	(17)	2	(34)	3
Income before taxes	(36)	(20)	(72)	(41)
Net income attributable to WSFS	(27)	(15)	(55)	(31)
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	(53)	(147)	(105)	(293)
Income taxes	13	35	25	70
Net income attributable to WSFS	(40)	(112)	(80)	(223)
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	37	(37)	(74)	(58)
Income taxes	(9)	9	18	14
Net income attributable to WSFS	$ 28	$ (28)	(56)	(44)
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)