Noncontrolling Interests (Schedule of Redeemable Noncontrolling Interest) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Activity in redeemable noncontrolling interest
Beginning balance			$ 1,296,506
Net income (loss) attributable to redeemable noncontrolling interest	$ 6,440	$ (204,277)	90,822	$ (132,338)
Ending balance	1,533,978		1,533,978		$ 1,296,506
DaVinciRe Holdings Ltd.
Activity in redeemable noncontrolling interest
Beginning balance	1,082,425	1,019,918	1,011,659	994,458	994,458
Redemption of shares from redeemable noncontrolling interest, net of adjustments	(170)	(12,068)	(609)	(78,870)
Sale of shares to redeemable noncontrolling interests	0	0	0	23,921
Net income (loss) attributable to redeemable noncontrolling interest	3,730	(195,508)	74,935	(127,167)
Ending balance	1,085,985	812,342	1,085,985	812,342	1,011,659
RenaissanceRe Medici Fund Ltd.
Activity in redeemable noncontrolling interest
Beginning balance	411,003	222,165	284,847	181,136	181,136
Redemption of shares from redeemable noncontrolling interest, net of adjustments	(8,720)	(1,400)	(52,223)	(27,310)	(48,000)
Sale of shares to redeemable noncontrolling interests	43,000	9,391	199,482	72,732	149,200
Net income (loss) attributable to redeemable noncontrolling interest	2,710	(8,769)	15,887	(5,171)
Ending balance	$ 447,993	$ 221,387	$ 447,993	$ 221,387	$ 284,847

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Decrease in noncontrolling interest (for example, but not limited to, redeeming or purchasing the interests of noncontrolling shareholders, issuance of shares (interests) by the non-wholly owned subsidiary to the parent entity for other than cash, and a buyback of shares (interest) by the non-wholly owned subsidiary from the noncontrolling interests).

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Amount of Net Income (Loss) attributable to redeemable noncontrolling interest.

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Amount of increase in noncontrolling interest from subsidiary issuance of equity interests to noncontrolling interest holders.

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As of the reporting date, the aggregate carrying amount of all noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. This item includes noncontrolling interest holder's ownership (or holders' ownership) regardless of the type of equity interest (common, preferred, other) including all potential organizational (legal) forms of the investee entity.

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