Earnings Per Share (Computation Of Basic And Diluted Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net (loss) income (attributable) available to RenaissanceRe common shareholders	$ (504,812)	$ 146,825	$ (241,318)	$ 411,145
Amount allocated to participating common shareholders	(116)	(1,770)	(344)	(4,939)
Net (loss) income allocated to RenaissanceRe common shareholders	$ (504,928)	$ 145,055	$ (241,662)	$ 406,206
Denominator:
Denominator for basic (loss) income per RenaissanceRe common share - weighted average common shares	39,591	40,513	39,979	41,594
Per common share equivalents of employee stock options and restricted shares (in shares)	0	220	0	248
Denominator for diluted (loss) income per RenaissanceRe common share - adjusted weighted average common shares and assumed conversions	39,591	40,733	39,979	41,842
Net (loss) income (attributable) available to RenaissanceRe common shareholders per common share – basic (in dollars per share)	$ (12.75)	$ 3.58	$ (6.04)	$ 9.77
Net (loss) income (attributable) available to RenaissanceRe common shareholders per common share – diluted (in dollars per share)	$ (12.75)	$ 3.56	$ (6.04)	$ 9.71

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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The earnings that is allocated to common stock and participating securities to the extent that each security may share in earnings as if all of the earnings for the period had been distributed.

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Amount of undistributed earnings (loss) allocated to participating securities for the basic earnings (loss) per share or per unit calculation under the two-class method.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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