Securities - Narrative (Details)	3 Months Ended
Mar. 31, 2018 USD ($) security institution	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Available for sale debt securities	$ 961,589,000	$ 2,496,000	$ 674,104,000
Sale proceeds		$ 2,496,000
Fair Value	$ 948,365,000		671,488,000
Number of institutions issuing debt (more than) \| institution	160
Trust preferred securities
Schedule of Available-for-sale Securities [Line Items]
Available for sale debt securities	$ 12,429,000		12,442,000
Fair Value	$ 10,045,000		9,388,000
Number of securities representing interests in tranches of trusts (tranches) \| security	2
Impairments	$ 0
Secure government, public and trust deposits
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities pledged as collateral	259,688,000		217,867,000
Short-term borrowings
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities pledged as collateral	20,644,000		25,888,000
Trust preferred securities
Schedule of Available-for-sale Securities [Line Items]
Available for sale debt securities	12,429,000		12,442,000
Fair Value	10,045,000		9,388,000
Government agency mortgage backed securities \| Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available for sale debt securities	416,954,000		196,121,000
Fair Value	409,470,000		193,950,000
Government agency collateralized mortgage obligations \| Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available for sale debt securities	244,213,000		180,258,000
Fair Value	237,666,000		176,639,000
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Available for sale debt securities	222,814,000		228,589,000
Fair Value	$ 226,342,000		$ 234,481,000

Number of institutions issuing debt.

No definition available.

Name:	rnst_NumberOfInstitutionsIssuingDebt
Namespace Prefix:	rnst_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of securities representing interests in tranches of trusts.

+ References

No definition available.

+ Details

Name:	rnst_NumberOfSecuritiesRepresentingInterestsInTranchesOfTrusts
Namespace Prefix:	rnst_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount of debt securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 320
-Section 50
-Paragraph 2
-Subparagraph (b)-(g)
-URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62557-112803

+ Details

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

- Definition

The fair value of available-for-sale securities that serve as collateral for borrowings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

+ Details

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

- Definition

This element represents the amount of loss recognized for other than temporary impairments (OTTI) of investments in debt and equity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 5.M)
-URI http://asc.fasb.org/extlink&oid=65877573&loc=d3e87990-122713

+ Details

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

- Definition

The cash inflow associated with the sale of debt securities classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26853-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

+ Details

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

- Details

Name:	us-gaap_CashAndCashEquivalentsAxis=rnst_TrustPreferredSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=rnst_SecureGovernmentPublicAndTrustDepositsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_ShortTermDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=rnst_TrustPreferredSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=rnst_GovernmentAgencyMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=rnst_GovernmentAgencyCollateralizedMortgageObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: