Segment Reporting (Schedule Of Significant Components Of The Company's Revenues And Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Gross premiums written	$ 407,766	$ 640,269	$ 827,415	$ 922,090	$ 323,091	$ 430,224	$ 759,128	$ 862,133	$ 2,797,540	$ 2,374,576	$ 2,011,310
Net premiums written	288,223	483,221	555,745	544,136	219,499	284,222	519,916	511,675	1,871,325	1,535,312	1,416,183
Net premiums earned	421,473	547,792	382,265	366,045	351,901	346,521	351,402	353,606	1,717,575	1,403,430	1,400,551
Net claims and claim expenses incurred	304,064	1,221,696	142,587	193,081	123,901	112,575	167,750	126,605	1,861,428	530,831	448,238
Acquisition expenses	98,598	76,761	88,251	83,282	74,146	80,580	69,005	65,592	346,892	289,323	238,592
Operational expenses	29,192	42,537	41,766	47,283	49,948	40,493	51,073	56,235	160,778	197,749	219,112
Underwriting (loss) income									(651,523)	385,527	494,609
Net investment income	73,464	40,257	54,163	54,325	47,316	51,423	54,124	28,863	222,209	181,726	152,567
Net foreign exchange gains (losses)	(490)	(156)	3,109	8,165	(5,420)	(5,986)	(690)	(1,692)	10,628	(13,788)	(3,051)
Equity in (losses) earnings of other ventures	2,200	1,794	5,543	(1,507)	4,960	(11,630)	6,022	1,611	8,030	963	20,481
Other income	2,362	2,996	2,392	1,665	5,177	2,268	2,654	4,079	9,415	14,178	13,472
Net realized and unrealized gains (losses) on investments	(7,716)	42,052	58,113	43,373	(49,967)	59,870	69,772	61,653	135,822	141,328	(68,918)
Corporate expenses	(4,237)	(4,413)	(4,636)	(5,286)	(11,888)	(11,537)	(5,752)	(8,225)	(18,572)	(37,402)	(76,514)
Interest expense	(11,777)	(11,799)	(10,091)	(10,526)	(10,534)	(10,536)	(10,536)	(10,538)	(44,193)	(42,144)	(36,270)
(Loss) income before taxes	43,425	(722,471)	218,254	132,608	83,550	186,745	179,168	180,925	(328,184)	630,388	496,376
Income tax (expense) benefit	(41,226)	18,977	(3,904)	(334)	7,700	1,316	(6,612)	(2,744)	(26,487)	(340)	45,866
Net (income) loss attributable to redeemable noncontrolling interests	(56)	204,277	(37,612)	(34,327)	(16,219)	(35,641)	(30,635)	(44,591)	132,282	(127,086)	(111,050)
Dividends on preference shares	(5,595)	(5,595)	(5,596)	(5,595)	(5,595)	(5,595)	(5,596)	(5,595)	(22,381)	(22,381)	(22,381)
Net (loss) income (attributable) available to RenaissanceRe common shareholders	$ (3,452)	$ (504,812)	$ 171,142	$ 92,352	$ 69,436	$ 146,825	$ 136,325	$ 127,995	(244,770)	480,581	408,811
Net claims and claim expenses incurred – current accident year									1,902,424	694,957	610,685
Net claims and claim expenses incurred – prior accident years									(40,996)	(164,126)	(162,447)
Total net incurred									$ 1,861,428	$ 530,831	$ 448,238
Net claims and claim expense ratio – current accident year									110.80%	49.50%	43.60%
Net claims and claim expense ratio – prior accident years									(2.40%)	(11.70%)	(11.60%)
Net claims and claim expense ratio – calendar year									108.40%	37.80%	32.00%
Underwriting expense ratio									29.50%	34.70%	32.70%
Combined ratio									137.90%	72.50%	64.70%
Other
Segment Reporting Information [Line Items]
Gross premiums written									$ (7)	$ 0	$ (90)
Net premiums written									4	143	(48)
Net premiums earned									4	142	(48)
Net claims and claim expenses incurred									(1,583)	(1,110)	(870)
Acquisition expenses									(1)	0	248
Operational expenses									36	123	266
Underwriting (loss) income									1,552	1,129	308
Net investment income									222,209	181,726	152,567
Net foreign exchange gains (losses)									10,628	(13,788)	(3,051)
Equity in (losses) earnings of other ventures									8,030	963	20,481
Other income									9,415	14,178	13,472
Net realized and unrealized gains (losses) on investments									135,822	141,328	(68,918)
Corporate expenses									(18,572)	(37,402)	(76,514)
Interest expense									(44,193)	(42,144)	(36,270)
Income tax (expense) benefit									(26,487)	(340)	45,866
Net (income) loss attributable to redeemable noncontrolling interests									132,282	(127,086)	(111,050)
Dividends on preference shares									(22,381)	(22,381)	(22,381)
Net claims and claim expenses incurred – current accident year									0	0	0
Net claims and claim expenses incurred – prior accident years									(1,583)	(1,110)	(870)
Total net incurred									(1,583)	(1,110)	(870)
Property
Segment Reporting Information [Line Items]
Gross premiums written									1,440,437	1,111,263	1,072,159
Net claims and claim expenses incurred – prior accident years									(45,596)	(104,876)	(93,786)
Property | Operating Segments
Segment Reporting Information [Line Items]
Gross premiums written									1,440,437	1,111,263	1,072,159
Net premiums written									978,014	725,321	726,145
Net premiums earned									931,070	720,951	805,985
Net claims and claim expenses incurred									1,297,985	151,545	128,290
Acquisition expenses									113,816	97,594	94,249
Operational expenses									94,194	108,642	118,666
Underwriting (loss) income									(574,925)	363,170	464,780
Net claims and claim expenses incurred – current accident year									1,343,581	256,421	222,076
Net claims and claim expenses incurred – prior accident years									(45,596)	(104,876)	(93,786)
Total net incurred									$ 1,297,985	$ 151,545	$ 128,290
Net claims and claim expense ratio – current accident year									144.30%	35.60%	27.60%
Net claims and claim expense ratio – prior accident years									(4.90%)	(14.60%)	(11.70%)
Net claims and claim expense ratio – calendar year									139.40%	21.00%	15.90%
Underwriting expense ratio									22.30%	28.60%	26.40%
Combined ratio									161.70%	49.60%	42.30%
Casualty and Specialty
Segment Reporting Information [Line Items]
Gross premiums written									$ 1,357,110	$ 1,263,313	$ 939,241
Net claims and claim expenses incurred – prior accident years									6,183	(58,140)	(67,791)
Casualty and Specialty | Operating Segments
Segment Reporting Information [Line Items]
Gross premiums written									1,357,110	1,263,313	939,241
Net premiums written									893,307	809,848	690,086
Net premiums earned									786,501	682,337	594,614
Net claims and claim expenses incurred									565,026	380,396	320,818
Acquisition expenses									233,077	191,729	144,095
Operational expenses									66,548	88,984	100,180
Underwriting (loss) income									(78,150)	21,228	29,521
Net claims and claim expenses incurred – current accident year									558,843	438,536	388,609
Net claims and claim expenses incurred – prior accident years									6,183	(58,140)	(67,791)
Total net incurred									$ 565,026	$ 380,396	$ 320,818
Net claims and claim expense ratio – current accident year									71.10%	64.30%	65.40%
Net claims and claim expense ratio – prior accident years									0.70%	(8.60%)	(11.40%)
Net claims and claim expense ratio – calendar year									71.80%	55.70%	54.00%
Underwriting expense ratio									38.10%	41.20%	41.00%
Combined ratio									109.90%	96.90%	95.00%