Stockholders' Equity and Regulatory Capital - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2005	Dec. 31, 2016	Dec. 31, 2015	May 31, 2015
Capital Unit [Line Items]
Ratio of common equity Tier 1 capital to risk-weighted assets	4.50%		4.50%
Ratio of Tier 1 capital to risk-weighted assets	10.70%		10.47%
Ratio of total capital to risk-weighted assets	11.41%		11.20%
Tier 1 leverage ratio	9.15%		9.02%
Common stock outstanding, par value (in dollars per share)	$ 0.01		$ 0.01		$ 0.01
Coupon rate	3.25%
Cash remains at the holding company	$ 37.3
Additional Stock Buyback Program
Capital Unit [Line Items]
Shares authorized to repurchase of common stock (in shares)	255,000
Common stock average repurchase price (in dollars per share)	$ 46.04
Remaining shares authorized to repurchase of common stock (in shares)	699,194
Percentage of remaining shares authorized to repurchase of common stock	2.00%
Shares outstanding (in shares)	31,400,000
Minimum
Capital Unit [Line Items]
Ratio of common equity Tier 1 capital to risk-weighted assets	4.50%
Ratio of Tier 1 capital to risk-weighted assets	6.00%
Ratio of total capital to risk-weighted assets	8.00%
Tier 1 leverage ratio	4.00%
Maximum
Capital Unit [Line Items]
Percentage of common stock shares approved				5.00%
WSFS Capital Trust III
Capital Unit [Line Items]
Pooled floating rate securities, par value		$ 2.0
Pooled floating rate securities issued		$ 67.0
Trust preferred borrowings | LIBOR Rate | WSFS Capital Trust III
Capital Unit [Line Items]
Variable interest rate		1.77%