Securities (Details Textual) (USD $)	12 Months Ended
Dec. 31, 2014 Tranche Institution	Dec. 31, 2013	Dec. 31, 2012
Securities (Additional Textual) [Abstract]
Carrying value of securities held to maturity		$ 4,292,000
Net gain recognized on sale of securities held to maturity		169,000
Securities classified as held to maturity	0rnst_HeldToMaturitiesSecuritiesSold		0rnst_HeldToMaturitiesSecuritiesSold
Securities (Textual) [Abstract]
Investments in pooled trust preferred securities, cost basis	553,770,000
Fair Value	553,584,000us-gaap_AvailableForSaleSecurities	501,254,000us-gaap_AvailableForSaleSecurities
Number of securities representing interests in tranches of trusts (tranches)	4
Number of institutions issuing debt (institutions)	320rnst_NumberOfInstitutionsIssuingDebt
Other than temporary impairment losses	0	0
Trust preferred securities
Securities (Textual) [Abstract]
Investments in pooled trust preferred securities, cost basis	26,400,000	27,531,000
Fair Value	19,756,000	17,671,000
Other than temporary impairment losses	0	0	0
Secure government, public and trust deposits
Securities (Textual) [Abstract]
Available for sale securities pledged as collateral	617,189,000	604,571,000
Short-term borrowings
Securities (Textual) [Abstract]
Available for sale securities pledged as collateral	$ 16,410,000	$ 7,626,000

Held to maturities securities sold.

No definition available.

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- Definition

Number of institutions issuing debt.

+ References

No definition available.

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- Definition

Number of securities representing interests in tranches of trusts.

+ References

No definition available.

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- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

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- Definition

The fair value of available-for-sale securities that serve as collateral for borrowings.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 5

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- Definition

For any sales of securities categorized as held-to-maturity, this item represents the net carrying amount of the sold security.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

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-Paragraph 10

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- Definition

This item represents the gain (loss) realized on the sale of held-to-maturity securities disposed of during the period. Additionally, this item may include, if not separately presented, any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt securities which are being or have been recognized in earnings during the period.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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- Definition

This element represents the amount of loss recognized for other than temporary impairments (OTTI) of investments in debt and equity securities.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

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-Paragraph 1

-Subparagraph (SAB TOPIC 5.M)

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