Purchase Credit Impaired ("PCI") Loans - Rollforward of Covered Loans, Net of the Allowance for Loan Losses (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 125,100	$ 189,571
Principal reductions and interest payments	(25,261)	(37,421)
Accretion of loan discount	12,323	19,987
Changes in contractual and expected cash flows due to remeasurement	5,262	5,841
Reductions due to disposals	(19,106)	(32,798)
Balance at end of period	98,318	145,180
Contractual Cashflows
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	266,068	386,966
Principal reductions and interest payments	(25,261)	(37,421)
Accretion of loan discount	0	0
Changes in contractual and expected cash flows due to remeasurement	(2,616)	9,216
Reductions due to disposals	(30,334)	(68,953)
Balance at end of period	207,857	289,808
Less: Non-accretable Difference
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	87,438	118,627
Principal reductions and interest payments	0	0
Accretion of loan discount	0	0
Changes in contractual and expected cash flows due to remeasurement	(7,378)	(10,858)
Reductions due to disposals	(7,379)	(23,867)
Balance at end of period	72,681	83,902
Less: Accretable Yield
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	53,530	78,768
Principal reductions and interest payments	0	0
Accretion of loan discount	(12,323)	(19,987)
Changes in contractual and expected cash flows due to remeasurement	(500)	14,233
Reductions due to disposals	(3,849)	(12,288)
Balance at end of period	$ 36,858	$ 60,726

Principal reductions and interest payments

No definition available.

Name:	efsc_Principalreductionsandinterestpayments
Namespace Prefix:	efsc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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

- Definition

Amount of the excess of a loan's cash flows expected to be collected over the investor's initial investment in 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 15

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=27045933&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=6379141&loc=d3e15032-111544

+ Details

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

- Definition

Amount of decrease from accretion of the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

+ References

+ Details

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

- Definition

Amount of reduction, resulting from a sale or transfer of a loan, in the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

+ References

+ Details

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

- Definition

Amount of increase of reclassification from nonaccretable difference to the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

+ References

+ Details

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