Loans - Summary of Portfolio Loans Individually Evaluated for Impairment by Category (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Related Allowance				$ 1,200
Portfolio loans, net
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	$ 3,623	$ 1,533	$ 2,422
Unpaid Contractual Principal Balance				15,660	$ 15,057
Recorded Investment With No Allowance				7,656	3,241
Recorded Investment With Allowance				1,329	12,150
Total Recorded Investment				8,985	15,391
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment				2,417	3,064
Impaired Financing Receivable, Related Allowance				2,374	3,064
Average Recorded Investment				13,290	7,366
Financing Receivable, Allowance for Credit Losses, Write-downs	(6,389)	(171)	(1,236)
Financing Receivable, Allowance for Credit Losses, Recovery	291	221	433
Financing Receivable, Allowance for Credit Losses	36,673	39,148	38,292	38,292	37,565
Portfolio loans, net \| Commercial and industrial
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	2,955	1,835	1,126
Unpaid Contractual Principal Balance				13,981	12,341
Recorded Investment With No Allowance				6,407	566
Recorded Investment With Allowance				1,044	11,791
Total Recorded Investment				7,451	12,357
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment				2,063	2,909
Impaired Financing Receivable, Related Allowance				2,020	2,909
Average Recorded Investment				11,735	4,489
Financing Receivable, Allowance for Credit Losses, Write-downs	(6,035)	(133)	(613)
Financing Receivable, Allowance for Credit Losses, Recovery	57	80	205
Financing Receivable, Allowance for Credit Losses	25,755	28,778	26,473	26,473	26,996
Portfolio loans, net \| Commercial - owner occupied
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	(354)	(249)	245
Unpaid Contractual Principal Balance				0	225
Recorded Investment With No Allowance				0	231
Recorded Investment With Allowance				0	0
Total Recorded Investment				0	231
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment				0	0
Impaired Financing Receivable, Related Allowance				0	0
Average Recorded Investment				0	227
Financing Receivable, Allowance for Credit Losses, Write-downs	(45)	0	(45)
Financing Receivable, Allowance for Credit Losses, Recovery	1	89	6
Financing Receivable, Allowance for Credit Losses	3,040	2,730	3,246	3,246	2,890
Portfolio loans, net \| Commercial - investor owned
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	39	(105)	376
Unpaid Contractual Principal Balance				562	525
Recorded Investment With No Allowance				259	435
Recorded Investment With Allowance				285	0
Total Recorded Investment				544	435
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment				120	0
Impaired Financing Receivable, Related Allowance				120	0
Average Recorded Investment				542	668
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0
Financing Receivable, Allowance for Credit Losses, Recovery	102	9	12
Financing Receivable, Allowance for Credit Losses	3,387	3,324	3,775	3,775	3,420
Portfolio loans, net \| Construction and land development
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	51	(11)	305
Unpaid Contractual Principal Balance				444	1,904
Recorded Investment With No Allowance				322	1,947
Recorded Investment With Allowance				0	359
Total Recorded Investment				322	2,306
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment				186	155
Impaired Financing Receivable, Related Allowance				186	155
Average Recorded Investment				337	1,918
Financing Receivable, Allowance for Credit Losses, Write-downs	(5)	0	0
Financing Receivable, Allowance for Credit Losses, Recovery	49	9	25
Financing Receivable, Allowance for Credit Losses	1,295	1,302	1,625	1,625	1,304
Portfolio loans, net \| Residential real estate
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	451	(3)	299
Unpaid Contractual Principal Balance				673	62
Recorded Investment With No Allowance				668	62
Recorded Investment With Allowance				0	0
Total Recorded Investment				668	62
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment				48	0
Impaired Financing Receivable, Related Allowance				48	0
Average Recorded Investment				676	64
Financing Receivable, Allowance for Credit Losses, Write-downs	(265)	(9)	(503)
Financing Receivable, Allowance for Credit Losses, Recovery	62	25	172
Financing Receivable, Allowance for Credit Losses	2,284	2,036	2,252	2,252	2,023
Portfolio loans, net \| Consumer and other
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	(47)	66	71
Unpaid Contractual Principal Balance				0	0
Recorded Investment With No Allowance				0	0
Recorded Investment With Allowance				0	0
Total Recorded Investment				0	0
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment				0	0
Impaired Financing Receivable, Related Allowance				0	0
Average Recorded Investment				0	0
Financing Receivable, Allowance for Credit Losses, Write-downs	(39)	(29)	(75)
Financing Receivable, Allowance for Credit Losses, Recovery	20	9	13
Financing Receivable, Allowance for Credit Losses	$ 912	$ 978	$ 921	$ 921	$ 932

A valuation allowance for financing receivables that are expected to be uncollectible.

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of direct write-downs of financing receivables charged against the allowance.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953550-111524

+ Details

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

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

+ Details

Name:	us-gaap_ProvisionForLoanLeaseAndOtherLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	efsc_LoansByMajorCategoryAxis=efsc_NoncoveredLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=efsc_CommercialAndIndustrialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=efsc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=efsc_CommercialRealEstateInvestorOwnedFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=efsc_ConstructionAndLandDevelopmentFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=efsc_ResidentialRealEstateFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=efsc_ConsumerAndOtherPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: