Investments in Qualified Affordable Housing Projects - Components of Qualified Affordable Housing Projects Included in Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Tax credit amortization	$ 394	$ 262
Tax credits and other benefits	(572)	(460)
Total	$ (178)	$ (198)

Affordable Housing Tax Credits and Other Benefits, Net of Amortization

No definition available.

Name:	rnst_AffordableHousingTaxCreditsandOtherBenefitsNetofAmortization
Namespace Prefix:	rnst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of affordable housing tax credits and other tax benefits recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=64813897&loc=SL49122993-202985

+ Details

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

- Definition

Amount of amortization expense of investment in qualified affordable housing projects.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64813897&loc=SL49122993-202985

+ Details

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

- References

No definition available.

+ Details

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