Purchased Loans - Restructured Loans by Class (Details) - Purchased $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| loan	5	5	28
Pre-Modification Outstanding Recorded Investment	$ 2,931	$ 712	$ 6,859
Post-Modification Outstanding Recorded Investment	$ 2,927	$ 552	$ 5,358
Commercial, financial, agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| loan	2	1
Pre-Modification Outstanding Recorded Investment	$ 2,778	$ 48
Post-Modification Outstanding Recorded Investment	$ 2,778	$ 44
Real estate – 1-4 family mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| loan	2	2	23
Pre-Modification Outstanding Recorded Investment	$ 73	$ 142	$ 3,744
Post-Modification Outstanding Recorded Investment	$ 73	$ 127	$ 3,127
Real estate – commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans \| loan	1	2	5
Pre-Modification Outstanding Recorded Investment	$ 80	$ 522	$ 3,115
Post-Modification Outstanding Recorded Investment	$ 76	$ 381	$ 2,231

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.

No definition available.

+ Details

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
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: