Purchased Loans - Impact of Modifications Classified as Restructured Loans (Details) - Purchased loans $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019 USD ($) loan	Jun. 30, 2018 USD ($) loan	Jun. 30, 2019 USD ($) loan	Jun. 30, 2018 USD ($) loan
Restructured loans
Number of Loans \| loan	2	1	2	3
Pre- Modification Outstanding Recorded Investment	$ 2,600	$ 18	$ 2,600	$ 74
Post- Modification Outstanding Recorded Investment	$ 2,596	$ 17	$ 2,596	$ 68
Commercial, financial, agricultural
Restructured loans
Number of Loans \| loan	1		1	1
Pre- Modification Outstanding Recorded Investment	$ 2,520		$ 2,520	$ 48
Post- Modification Outstanding Recorded Investment	$ 2,520		$ 2,520	$ 44
Real estate – 1-4 family mortgage
Restructured loans
Number of Loans \| loan		1		1
Pre- Modification Outstanding Recorded Investment		$ 18		$ 18
Post- Modification Outstanding Recorded Investment		$ 17		$ 17
Real estate – commercial mortgage
Restructured loans
Number of Loans \| loan	1		1	1
Pre- Modification Outstanding Recorded Investment	$ 80		$ 80	$ 8
Post- Modification Outstanding Recorded Investment	$ 76		$ 76	$ 7

Troubled Debt Restructuring Financing Receivable Modifications [Abstract]

No definition available.

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=rnst_LoanPortfolioPurchasedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=rnst_RealEstateOneToFourFamilyMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=rnst_CommercialResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: