CHANGE IN ACCUMULATED OTHER COMPREHENSIVE LOSS - Components of Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains on securities transactions	$ 15	$ 21
Income taxes	(6,260)	(10,769)
Income before taxes	19,190	48,119
Net income attributable to WSFS	13,023	37,350
Prior service cost (credit), tax adjustment		100
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income attributable to WSFS	(144)	(76)
Reclassification out of Accumulated Other Comprehensive Income \| Net change in defined benefit plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	(8)	11
Prior service costs (credits)	(19)	59
Actuarial gains	(15)	(11)
Income before taxes	(34)	48
Net income attributable to WSFS	(42)	59
Reclassification out of Accumulated Other Comprehensive Income \| 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	(15)	(21)
Income taxes	4	5
Net income attributable to WSFS	(11)	(16)
Reclassification out of Accumulated Other Comprehensive Income \| 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	29	37
Amortization of net unrealized gains to income during the period	(120)	(156)
Net income attributable to WSFS	$ (91)	$ (119)

Amount of unrealized and realized gain (loss) on investment in debt and equity securities.

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