Non Purchased Loans - Impaired Loans Recognized (Details) - Non-Purchased - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impaired loans
Recorded Investment With Allowance	$ 21,040	$ 21,039
Recorded Investment With No Allowance	703	568
Total Recorded Investment	21,743	21,607
Unpaid Principal Balance With Allowance	25,679	26,633
Unpaid Principal Balance With no Allowance	703	1,378
Total Unpaid Principal Balance	26,382	28,011
With Related Allowance	2,567	3,626
With No Related Allowance	0	0
Related Allowance	2,567	3,626
Average Recorded Investment With Related Allowance	21,287	22,206
Average Recorded Investment With No Related Allowance	711	1,003
Average recorded investment in impaired loans	21,998	23,209	$ 34,428
Interest Income Recognized With Related Allowance	544	586
Interest Income Recognized With No Related Allowance	29	38
Interest Income, Total	573	624
Commercial, financial, agricultural
Impaired loans
Recorded Investment With Allowance	2,365	1,175
Recorded Investment With No Allowance	0	0
Unpaid Principal Balance With Allowance	3,043	1,539
Unpaid Principal Balance With no Allowance	0	38
With Related Allowance	138	136
With No Related Allowance	0	0
Average Recorded Investment With Related Allowance	2,861	856
Average Recorded Investment With No Related Allowance	0	24
Interest Income Recognized With Related Allowance	47	28
Interest Income Recognized With No Related Allowance	0	0
Lease financing
Impaired loans
Recorded Investment With Allowance	159	0
Recorded Investment With No Allowance	0	0
Unpaid Principal Balance With Allowance	159	0
Unpaid Principal Balance With no Allowance	0	0
With Related Allowance	2	0
With No Related Allowance	0	0
Average Recorded Investment With Related Allowance	159	0
Average Recorded Investment With No Related Allowance	0	0
Interest Income Recognized With Related Allowance	0	0
Interest Income Recognized With No Related Allowance	0	0
Real estate – construction
Impaired loans
Recorded Investment With Allowance	578	517
Recorded Investment With No Allowance	0	0
Unpaid Principal Balance With Allowance	578	517
Unpaid Principal Balance With no Allowance	0	0
With Related Allowance	4	1
With No Related Allowance	0	0
Average Recorded Investment With Related Allowance	526	469
Average Recorded Investment With No Related Allowance	0	0
Interest Income Recognized With Related Allowance	29	26
Interest Income Recognized With No Related Allowance	0	0
Real estate – 1-4 family mortgage
Impaired loans
Recorded Investment With Allowance	8,169	9,207
Recorded Investment With No Allowance	703	0
Unpaid Principal Balance With Allowance	9,315	10,823
Unpaid Principal Balance With no Allowance	703	0
With Related Allowance	561	1,091
With No Related Allowance	0	0
Average Recorded Investment With Related Allowance	8,295	9,603
Average Recorded Investment With No Related Allowance	711	41
Interest Income Recognized With Related Allowance	259	225
Interest Income Recognized With No Related Allowance	29	0
Real estate – commercial mortgage
Impaired loans
Recorded Investment With Allowance	9,652	10,053
Recorded Investment With No Allowance	0	568
Unpaid Principal Balance With Allowance	12,463	13,667
Unpaid Principal Balance With no Allowance	0	1,340
With Related Allowance	1,861	2,397
With No Related Allowance	0	0
Average Recorded Investment With Related Allowance	9,316	11,180
Average Recorded Investment With No Related Allowance	0	938
Interest Income Recognized With Related Allowance	206	305
Interest Income Recognized With No Related Allowance	0	38
Installment loans to individuals
Impaired loans
Recorded Investment With Allowance	117	87
Recorded Investment With No Allowance	0	0
Unpaid Principal Balance With Allowance	121	87
Unpaid Principal Balance With no Allowance	0	0
With Related Allowance	1	1
With No Related Allowance	0	0
Average Recorded Investment With Related Allowance	130	98
Average Recorded Investment With No Related Allowance	0	0
Interest Income Recognized With Related Allowance	3	2
Interest Income Recognized With No Related Allowance	$ 0	$ 0

Impaired financing receivable with no related allowance.

No definition available.

Name:	rnst_ImpairedFinancingReceivableWithNoRelatedAllowance
Namespace Prefix:	rnst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Impaired financing receivable with related allowance.

+ References

No definition available.

+ Details

Name:	rnst_ImpairedFinancingReceivableWithRelatedAllowance
Namespace Prefix:	rnst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

+ Details

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

- Definition

Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953550-111524

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

+ Details

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

- Definition

Amount of interest income, recognized on cash basis, on financing receivables, for which there is no related allowance for credit losses and are recognized as impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of interest income on financing receivables, for which there is a related allowance for credit losses, recognized on a cash-basis method of accounting that the financing receivables were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
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:

- Details

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