Derivative instruments.

No definition available.

Name:	rnst_DerivativeInstrumentsTextualAbstract
Namespace Prefix:	rnst_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

+ Details

Name:	us-gaap_DerivativeNumberOfInstrumentsHeld
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=rnst_InterestRateContractsWithCorporateCustomersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=rnst_OffsettingInterestRateContractsWithOtherFinancialInstitutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=rnst_InterestRateSwapFloatingRateLiabilityattheBankLevelDerivativeOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=rnst_InterestRateSwapFloatingRateLiabilityattheBankLevelDerivativeTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=rnst_CommitmentsToFundFixedRateResidentialMortgageLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=rnst_CommitmentsToSellResidentialMortgageLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Derivative Instruments - Narrative (Details) $ in Thousands	1 Months Ended
Derivative Instruments - Narrative (Details) $ in Thousands	Jun. 30, 2014 USD ($) derivative_instrument	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Apr. 30, 2018 USD ($)	Apr. 30, 2012 USD ($) derivative_instrument
Interest rate contracts with corporate customers
Derivative Instruments (Textual) [Abstract]
Derivative, notional amount		$ 204,590
Offsetting interest rate contracts with other financial institutions
Derivative Instruments (Textual) [Abstract]
Derivative, notional amount		204,590
Interest rate swaps
Derivative Instruments (Textual) [Abstract]
Number of instruments held \| derivative_instrument	2
Floating rate liability at the bank level, derivative one
Derivative Instruments (Textual) [Abstract]
Derivative, notional amount	$ 15,000
Term of contract	4 years
Floating rate liability at the bank level, derivative two
Derivative Instruments (Textual) [Abstract]
Derivative, notional amount	$ 15,000
Term of contract	5 years
Cash flow hedging
Derivative Instruments (Textual) [Abstract]
Derivative, notional amount				$ 30,000	$ 32,000
Number of instruments held \| derivative_instrument					2
Commitments to fund fixed-rate residential mortgage loans
Derivative Instruments (Textual) [Abstract]
Derivative, notional amount		316,330	$ 159,464
Commitments to sell residential mortgage loans
Derivative Instruments (Textual) [Abstract]
Derivative, notional amount		$ 593,000	$ 281,343