Purchased Loans - Impaired Loans and Average Recorded Investment and Interest Income Recognized (Details) - Purchased - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Impaired loans
Unpaid Contractual Principal Balance	$ 8,677		$ 9,203
Recorded Investment With Allowance	3,366		2,892
Recorded Investment With No Allowance	4,654		5,672
Total Recorded Investment	8,020		8,564
Related Allowance	170		107
Average Recorded Investment	8,737	$ 9,197
Interest Income Recognized	62	58
Receivables Acquired with Deteriorated Credit Quality
Impaired loans
Unpaid Contractual Principal Balance	262,379		277,709
Recorded Investment With Allowance	86,243		87,484
Recorded Investment With No Allowance	128,067		139,776
Total Recorded Investment	214,310		227,260
Related Allowance	1,817		1,777
Average Recorded Investment	244,700	291,340
Interest Income Recognized	2,888	3,452
Commercial, financial, agricultural
Impaired loans
Unpaid Contractual Principal Balance	421		757
Recorded Investment With Allowance	336		625
Recorded Investment With No Allowance	21		74
Total Recorded Investment	357		699
Related Allowance	49		52
Average Recorded Investment	363	541
Interest Income Recognized	3	2
Commercial, financial, agricultural \| Receivables Acquired with Deteriorated Credit Quality
Impaired loans
Unpaid Contractual Principal Balance	21,363		24,179
Recorded Investment With Allowance	5,414		5,768
Recorded Investment With No Allowance	7,519		9,547
Total Recorded Investment	12,933		15,315
Related Allowance	305		312
Average Recorded Investment	16,899	14,088
Interest Income Recognized	225	247
Real estate – construction
Impaired loans
Unpaid Contractual Principal Balance	252		1,207
Recorded Investment With Allowance	0		0
Recorded Investment With No Allowance	249		1,199
Total Recorded Investment	249		1,199
Related Allowance	0		0
Average Recorded Investment	252	0
Interest Income Recognized	1	0
Real estate – 1-4 family mortgage
Impaired loans
Unpaid Contractual Principal Balance	6,195		6,173
Recorded Investment With Allowance	1,493		1,385
Recorded Investment With No Allowance	4,133		4,225
Total Recorded Investment	5,626		5,610
Related Allowance	47		45
Average Recorded Investment	6,320	5,481
Interest Income Recognized	40	21
Real estate – 1-4 family mortgage \| Receivables Acquired with Deteriorated Credit Quality
Impaired loans
Unpaid Contractual Principal Balance	60,590		65,049
Recorded Investment With Allowance	16,093		15,910
Recorded Investment With No Allowance	34,103		38,059
Total Recorded Investment	50,196		53,969
Related Allowance	486		572
Average Recorded Investment	58,749	78,341
Interest Income Recognized	673	865
Real estate – commercial mortgage
Impaired loans
Unpaid Contractual Principal Balance	1,647		901
Recorded Investment With Allowance	1,384		728
Recorded Investment With No Allowance	245		165
Total Recorded Investment	1,629		893
Related Allowance	70		6
Average Recorded Investment	1,642	3,090
Interest Income Recognized	18	35
Real estate – commercial mortgage \| Receivables Acquired with Deteriorated Credit Quality
Impaired loans
Unpaid Contractual Principal Balance	178,682		186,720
Recorded Investment With Allowance	63,979		65,108
Recorded Investment With No Allowance	85,568		91,230
Total Recorded Investment	149,547		156,338
Related Allowance	1,023		892
Average Recorded Investment	167,365	196,807
Interest Income Recognized	1,972	2,319
Installment loans to individuals
Impaired loans
Unpaid Contractual Principal Balance	162		165
Recorded Investment With Allowance	153		154
Recorded Investment With No Allowance	6		9
Total Recorded Investment	159		163
Related Allowance	4		4
Average Recorded Investment	160	85
Interest Income Recognized	0	0
Installment loans to individuals \| Receivables Acquired with Deteriorated Credit Quality
Impaired loans
Unpaid Contractual Principal Balance	1,744		1,761
Recorded Investment With Allowance	757		698
Recorded Investment With No Allowance	877		940
Total Recorded Investment	1,634		1,638
Related Allowance	3		$ 1
Average Recorded Investment	1,687	2,104
Interest Income Recognized	$ 18	$ 21

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

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 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 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

- Details

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

- Details

Name:	us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis=us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
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=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: