Segment Reporting (Schedule Of Significant Components Of The Company's Revenues And Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Gross premiums written	$ 1,159,652	$ 922,090
Net premiums written	663,044	544,136
Net premiums earned	440,282	366,045
Net claims and claim expenses incurred	171,703	193,081
Acquisition expenses	97,711	83,282
Operational expenses	41,272	47,283
Underwriting income (loss)	129,596	42,399
Net investment income	56,476	54,325
Net foreign exchange gains	3,757	8,165
Equity in earnings (losses) of other ventures	857	(1,507)
Other (loss) income	(1,242)	1,665
Net realized and unrealized (losses) gains on investments	(82,144)	43,373
Corporate expenses	(6,733)	(5,286)
Interest expense	(11,767)	(10,526)
Income before taxes	88,800	132,608
Income tax benefit (expense)	3,407	(334)
Net income attributable to redeemable noncontrolling interests	(29,899)	(34,327)
Dividends on preference shares	(5,595)	(5,595)
Net income available to RenaissanceRe common shareholders	56,713	92,352
Net claims and claim expenses incurred – current accident year	203,038	164,075
Net claims and claim expenses incurred – prior accident years	(31,335)	29,006
Total net incurred	$ 171,703	$ 193,081
Net claims and claim expense ratio – current accident year	46.10%	44.80%
Net claims and claim expense ratio – prior accident years	(7.10%)	7.90%
Net claims and claim expense ratio – calendar year	39.00%	52.70%
Underwriting expense ratio	31.60%	35.70%
Combined ratio	70.60%	88.40%
Other
Segment Reporting Information [Line Items]
Gross premiums written	$ 0	$ 0
Net premiums written	0	0
Net premiums earned	0	(2)
Net claims and claim expenses incurred	18	(328)
Acquisition expenses	0	0
Operational expenses	133	11
Underwriting income (loss)	(151)	315
Net investment income	56,476	54,325
Net foreign exchange gains	3,757	8,165
Equity in earnings (losses) of other ventures	857	(1,507)
Other (loss) income	(1,242)	1,665
Net realized and unrealized (losses) gains on investments	(82,144)	43,373
Corporate expenses	(6,733)	(5,286)
Interest expense	(11,767)	(10,526)
Income tax benefit (expense)	3,407	(334)
Net income attributable to redeemable noncontrolling interests	(29,899)	(34,327)
Dividends on preference shares	(5,595)	(5,595)
Net claims and claim expenses incurred – current accident year	0	0
Net claims and claim expenses incurred – prior accident years	18	(328)
Total net incurred	18	(328)
Property
Segment Reporting Information [Line Items]
Net claims and claim expenses incurred – prior accident years	(27,562)	(928)
Property | Operating Segments
Segment Reporting Information [Line Items]
Gross premiums written	706,968	520,529
Net premiums written	354,077	289,871
Net premiums earned	225,049	186,988
Net claims and claim expenses incurred	30,607	38,838
Acquisition expenses	40,721	29,103
Operational expenses	26,546	27,665
Underwriting income (loss)	127,175	91,382
Net claims and claim expenses incurred – current accident year	58,169	39,766
Net claims and claim expenses incurred – prior accident years	(27,562)	(928)
Total net incurred	$ 30,607	$ 38,838
Net claims and claim expense ratio – current accident year	25.80%	21.30%
Net claims and claim expense ratio – prior accident years	(12.20%)	(0.50%)
Net claims and claim expense ratio – calendar year	13.60%	20.80%
Underwriting expense ratio	29.90%	30.30%
Combined ratio	43.50%	51.10%
Casualty and Specialty
Segment Reporting Information [Line Items]
Net claims and claim expenses incurred – prior accident years	$ (3,791)	$ 30,262
Casualty and Specialty | Operating Segments
Segment Reporting Information [Line Items]
Gross premiums written	452,684	401,561
Net premiums written	308,967	254,265
Net premiums earned	215,233	179,059
Net claims and claim expenses incurred	141,078	154,571
Acquisition expenses	56,990	54,179
Operational expenses	14,593	19,607
Underwriting income (loss)	2,572	(49,298)
Net claims and claim expenses incurred – current accident year	144,869	124,309
Net claims and claim expenses incurred – prior accident years	(3,791)	30,262
Total net incurred	$ 141,078	$ 154,571
Net claims and claim expense ratio – current accident year	67.30%	69.40%
Net claims and claim expense ratio – prior accident years	(1.80%)	16.90%
Net claims and claim expense ratio – calendar year	65.50%	86.30%
Underwriting expense ratio	33.30%	41.20%
Combined ratio	98.80%	127.50%