Segment Reporting (Schedule Of Underwriting Results For Operating Segments) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Premiums earned	$ 1,332,398	$ 1,272,317	$ 2,639,475	$ 2,416,807
Incurred losses and LAE	790,661	735,697	1,513,126	1,355,106
Commission and brokerage	294,917	283,687	582,084	529,689
Other underwriting expenses	63,951	58,414	124,615	109,052
Underwriting gain (loss)	182,869	194,519	419,650	422,960
U.S. Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross written premium	421,810	437,475	927,357	933,116
Net written premiums	388,006	423,279	872,409	921,036
Premiums earned	480,848	489,129	991,942	918,770
Incurred losses and LAE	228,745	239,014	473,631	452,469
Commission and brokerage	120,171	122,766	242,955	215,734
Other underwriting expenses	11,807	11,454	23,336	20,936
Underwriting gain (loss)	120,125	115,895	252,020	229,631
International [Member]
Segment Reporting Information [Line Items]
Gross written premium	292,775	454,017	611,220	775,259
Net written premiums	316,656	315,590	578,394	624,627
Premiums earned	338,263	319,998	643,832	638,379
Incurred losses and LAE	222,087	204,433	401,739	367,607
Commission and brokerage	84,813	71,599	155,427	142,573
Other underwriting expenses	8,049	8,088	16,164	15,925
Underwriting gain (loss)	23,314	35,878	70,502	112,274
Bermuda [Member]
Segment Reporting Information [Line Items]
Gross written premium	162,536	185,036	338,330	368,451
Net written premiums	131,209	176,193	305,775	358,763
Premiums earned	198,297	191,259	394,001	364,945
Incurred losses and LAE	108,230	107,133	218,245	201,641
Commission and brokerage	47,243	46,839	98,376	92,547
Other underwriting expenses	8,788	8,159	17,588	16,445
Underwriting gain (loss)	34,036	29,128	59,792	54,312
U.S Insurance [Member]
Segment Reporting Information [Line Items]
Gross written premium	343,630	316,481	683,888	547,131
Net written premiums	299,848	280,073	603,429	491,741
Premiums earned	267,848	248,283	527,969	451,520
Incurred losses and LAE	219,123	175,033	399,724	317,224
Commission and brokerage	38,294	39,908	76,857	74,117
Other underwriting expenses	33,258	29,128	63,555	52,361
Underwriting gain (loss)	(22,827)	4,214	(12,167)	7,818
Mt. Logan Re [Member]
Segment Reporting Information [Line Items]
Gross written premium	37,497	22,353	111,494	58,829
Net written premiums	32,777	22,352	92,378	48,909
Premiums earned	47,142	23,648	81,731	43,193
Incurred losses and LAE	12,476	10,084	19,787	16,165
Commission and brokerage	4,396	2,575	8,469	4,718
Other underwriting expenses	2,049	1,585	3,972	3,385
Underwriting gain (loss)	$ 28,221	$ 9,404	$ 49,503	$ 18,925