SEGMENT INFORMATION - Details of Segment Information - Statement of Financial Condition (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Cash and cash equivalents	$ 711,089	$ 723,866	$ 855,263	$ 821,923
Goodwill	166,007	166,007
Other segment assets	6,110,835	6,109,667
Total assets	6,987,931	6,999,540
Capital expenditures	2,224	8,994
WSFS Bank
Segment Reporting Information [Line Items]
Cash and cash equivalents	112,124	104,530
Goodwill	145,808	145,808
Other segment assets	5,880,317	5,882,910
Total assets	6,138,249	6,133,248
Capital expenditures	2,070	8,197
Cash Connect
Segment Reporting Information [Line Items]
Cash and cash equivalents	588,862	611,385
Goodwill	0	0
Other segment assets	6,717	6,078
Total assets	595,579	617,463
Capital expenditures	32	184
Wealth Management
Segment Reporting Information [Line Items]
Cash and cash equivalents	10,103	7,951
Goodwill	20,199	20,199
Other segment assets	223,801	220,679
Total assets	254,103	248,829
Capital expenditures	$ 122	$ 613