Loans - Summary of Portfolio Loans Individually Evaluated for Impairment by Category (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Related Allowance	$ 900		$ 900
Portfolio loans, net
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	(2,385)	$ (1,871)
Unpaid Contractual Principal Balance	24,834		24,834	$ 24,343
Recorded Investment With No Allowance	4,991		4,991	4,856
Recorded Investment With Allowance	9,810		9,810	10,831
Total Recorded Investment	14,801		14,801	15,687
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	3,886		3,886	2,579
Impaired Financing Receivable, Related Allowance	3,886		3,886	2,579
Average Recorded Investment			16,271	19,722
Financing Receivable, Allowance for Credit Losses, Write-downs	(1,027)	(1,035)
Financing Receivable, Allowance for Credit Losses, Recovery	386	1,261
Financing Receivable, Allowance for Credit Losses	42,007	40,263	42,007	38,166
Portfolio loans, net \| Commercial and industrial
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	(2,852)	(780)
Unpaid Contractual Principal Balance	20,915		20,915	20,750
Recorded Investment With No Allowance	1,900		1,900	2,321
Recorded Investment With Allowance	9,326		9,326	10,344
Total Recorded Investment	11,226		11,226	12,665
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	3,667		3,667	2,508
Impaired Financing Receivable, Related Allowance	3,667		3,667	2,508
Average Recorded Investment			12,591	16,270
Financing Receivable, Allowance for Credit Losses, Write-downs	(956)	(732)
Financing Receivable, Allowance for Credit Losses, Recovery	118	956
Financing Receivable, Allowance for Credit Losses	29,424	27,410	29,424	26,406
Portfolio loans, net \| Commercial - investor owned
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	(5)	(648)
Unpaid Contractual Principal Balance	557		557	560
Recorded Investment With No Allowance	410		410	422
Recorded Investment With Allowance	0		0	0
Total Recorded Investment	410		410	422
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0	0
Impaired Financing Receivable, Related Allowance	0		0	0
Average Recorded Investment			415	521
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Financing Receivable, Allowance for Credit Losses, Recovery	10	8
Financing Receivable, Allowance for Credit Losses	4,561	4,546	4,561	3,890
Portfolio loans, net \| Commercial - owner occupied
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	(340)	(190)
Unpaid Contractual Principal Balance	751		751	487
Recorded Investment With No Allowance	259		259	0
Recorded Investment With Allowance	484		484	487
Total Recorded Investment	743		743	487
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	219		219	71
Impaired Financing Receivable, Related Allowance	219		219	71
Average Recorded Investment			750	490
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Financing Receivable, Allowance for Credit Losses, Recovery	3	4
Financing Receivable, Allowance for Credit Losses	3,845	3,502	3,845	3,308
Portfolio loans, net \| Construction and land development
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	206	(35)
Unpaid Contractual Principal Balance	444		444	441
Recorded Investment With No Allowance	435		435	136
Recorded Investment With Allowance	0		0	0
Total Recorded Investment	435		435	136
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0	0
Impaired Financing Receivable, Related Allowance	0		0	0
Average Recorded Investment			494	331
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Financing Receivable, Allowance for Credit Losses, Recovery	168	206
Financing Receivable, Allowance for Credit Losses	1,690	1,728	1,690	1,487
Portfolio loans, net \| Residential real estate
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	573	(259)
Unpaid Contractual Principal Balance	1,835		1,835	1,730
Recorded Investment With No Allowance	1,669		1,669	1,602
Recorded Investment With Allowance	0		0	0
Total Recorded Investment	1,669		1,669	1,602
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0	0
Impaired Financing Receivable, Related Allowance	0		0	0
Average Recorded Investment			1,688	1,735
Financing Receivable, Allowance for Credit Losses, Write-downs	(38)	(254)
Financing Receivable, Allowance for Credit Losses, Recovery	59	73
Financing Receivable, Allowance for Credit Losses	1,763	2,315	1,763	2,237
Portfolio loans, net \| Consumer and other
Financing Receivable, Impaired [Line Items]
Provision for Loan, Lease, and Other Losses	33	41
Unpaid Contractual Principal Balance	332		332	375
Recorded Investment With No Allowance	318		318	375
Recorded Investment With Allowance	0		0	0
Total Recorded Investment	318		318	375
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0	0
Impaired Financing Receivable, Related Allowance	0		0	0
Average Recorded Investment			333	375
Financing Receivable, Allowance for Credit Losses, Write-downs	(33)	(49)
Financing Receivable, Allowance for Credit Losses, Recovery	28	14
Financing Receivable, Allowance for Credit Losses	$ 724	$ 762	$ 724	$ 838

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_CommercialRealEstateInvestorOwnedFinancingReceivableMember
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_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: