Acquired Credit Impaired Loans - Schedule of Loans Acquired Through Merger in Accordance with FASB ASC 310-30 (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Contractually required principal and interest at acquisition	$ 6,800	$ 15,000
Penn Liberty
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Contractually required principal and interest at acquisition	16,499
Contractual cash flows not expected to be collected (nonaccretable difference)	3,125
Expected cash flows at acquisition	13,374
Interest component of expected cash flows (accretable yield)	670
Fair value of acquired loans accounted for under FASB ASC 310-30	12,704
Alliance
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Contractually required principal and interest at acquisition	27,469
Contractual cash flows not expected to be collected (nonaccretable difference)	2,377
Expected cash flows at acquisition	25,092
Interest component of expected cash flows (accretable yield)	2,334
Fair value of acquired loans accounted for under FASB ASC 310-30	22,758
First National Bank of Wyoming (FNBW)
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Contractually required principal and interest at acquisition	27,086
Contractual cash flows not expected to be collected (nonaccretable difference)	7,956
Expected cash flows at acquisition	19,130
Interest component of expected cash flows (accretable yield)	1,790
Fair value of acquired loans accounted for under FASB ASC 310-30	17,340
Total
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Contractually required principal and interest at acquisition	71,054
Contractual cash flows not expected to be collected (nonaccretable difference)	13,458
Expected cash flows at acquisition	57,596
Interest component of expected cash flows (accretable yield)	4,794
Fair value of acquired loans accounted for under FASB ASC 310-30	$ 52,802

The aggregate excess of a loan's cash flows expected to be collected over the investor's initial investment in the loan for loans accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

+ Details

Name:	us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYield
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value at acquisition of acquired loans accounted for as debt securities with evidence of deterioration of credit quality.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

+ Details

Name:	us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodAtAcquisitionAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of cash flows expected to be collected at acquisition of acquired loans accounted for as debt securities with evidence of deterioration of credit quality.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

+ Details

Name:	us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodCashFlowsExpectedToBeCollectedAtAcquisition
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of the loan's contractually required payments receivable in excess of the amount of its cash flows expected to be collected. This relates to loans with deteriorating of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

+ References

No definition available.

+ Details

Name:	us-gaap_CertainLoansAcquiredInTransferNonaccretableDifference
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of contractually required payments receivable at acquisition of acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538

+ Details

Name:	us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractuallyRequiredPaymentsReceivableAtAcquisition
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_BusinessAcquisitionAxis=wsfs_PennLibertyFinancialCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=wsfs_AllianceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=wsfs_FirstWyomingFinancialCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=wsfs_BusinessAcquisitionsTotalLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: