CHANGE IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Components of Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains on securities transactions	$ 63	$ 0		$ 78	$ 21
Income taxes	(10,091)	(6,907)		(16,351)	(17,676)
Interest and dividends on investment securities	142,903	72,151		242,480	139,764
Income before taxes	46,060	35,647		65,250	83,766
Net income attributable to WSFS	36,200	28,740		49,223	66,090
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	(176)	(155)		(320)	(231)
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	(9)	(7)		(17)	4
Prior service costs (credits)	(19)	(19)		(38)	40
Transition obligation				0	0
Actuarial gains	(16)	(12)		(31)	(23)
Income before taxes	(35)	(31)		(69)	17
Net income attributable to WSFS	(44)	(38)		(86)	21
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	(63)	0		(78)	(21)
Income taxes	15	0		19	5
Net income attributable to WSFS	(48)	0		(59)	(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	27	36		56	73
Amortization of net unrealized gains to income during the period	(111)	(153)
Interest and dividends on investment securities				(231)	(309)
Net income attributable to WSFS	$ (84)	$ (117)		$ (175)	$ (236)

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

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