Segment Reporting (Schedule Of Underwriting Results For Operating Segments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Premiums earned	$ 1,218,867	$ 1,272,488
Incurred losses and LAE	700,749	715,155
Commission and brokerage	275,006	283,094
Other underwriting expenses	72,110	58,741
U.S. Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross written premium	536,706	562,647
Net written premiums	470,691	484,403
Premiums earned	486,541	511,094
Incurred losses and LAE	236,444	244,886
Commission and brokerage	117,317	122,784
Other underwriting expenses	13,459	11,529
Underwriting gain (loss)	119,321	131,895
International [Member]
Segment Reporting Information [Line Items]
Gross written premium	235,591	326,998
Net written premiums	202,500	261,738
Premiums earned	250,450	305,569
Incurred losses and LAE	147,535	179,652
Commission and brokerage	64,286	70,614
Other underwriting expenses	7,823	8,115
Underwriting gain (loss)	30,806	47,188
Bermuda [Member]
Segment Reporting Information [Line Items]
Gross written premium	204,732	188,121
Net written premiums	184,314	174,566
Premiums earned	194,428	195,704
Incurred losses and LAE	111,521	110,015
Commission and brokerage	49,922	51,133
Other underwriting expenses	9,185	8,800
Underwriting gain (loss)	23,800	25,756
Insurance [Member]
Segment Reporting Information [Line Items]
Gross written premium	376,160	340,258
Net written premiums	323,952	303,581
Premiums earned	287,448	260,121
Incurred losses and LAE	205,249	180,601
Commission and brokerage	43,481	38,563
Other underwriting expenses	41,643	30,297
Underwriting gain (loss)	$ (2,925)	$ 10,660