RESTRICTIONS ON CASH AND DIVIDENDS (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Restrictions on Subsidiary Dividends, Loans or Advances [Line Items]
Average Restriction on Cash and Due From Bank Accounts	$ 66.7	$ 58.9
Subsidiaries [Member]
Restrictions on Subsidiary Dividends, Loans or Advances [Line Items]
Retained Earnings, Unappropriated	546.5
Amount Available for Dividend Distribution without Affecting Capital Adequacy Requirements	$ 163.1

Average Cash Reserve Required of Subsidiary

No definition available.

Name:	ffbc_AverageCashReserveRequiredOfSubsidiary
Namespace Prefix:	ffbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Restrictions on Subsidiary Dividends, Loans or Advances [Line Items]

+ References

No definition available.

+ Details

Name:	ffbc_RestrictionsOnSubsidiaryDividendsLoansOrAdvancesLineItems
Namespace Prefix:	ffbc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of dividends that can be declared or paid without affecting the banking or savings institution's regulatory capital position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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

- Definition

A segregation of retained earnings which is available for dividend distribution. Earnings not paid out as dividends but instead reinvested in the core business or used to pay off debt. Unappropriated profit is part of shareholder equity. Also called cumulative distributions or earned surplus or accumulated earnings or unappropriated profit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(30)(a)(3)(ii))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(23)(a)(4)(ii))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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

- Details

Name:	us-gaap_ConsolidatedEntitiesAxis=us-gaap_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: