Segment Reporting (Schedule Of Underwriting Results For Operating Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting Information [Line Items]
Premiums earned	$ 1,144,490	$ 1,088,759
Incurred losses and LAE	619,409	592,644
Commission and brokerage	246,002	233,046
Other underwriting expenses	50,638	52,946
Underwriting gain (loss)	228,441	210,123
U.S. Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross written premiums	495,641	434,791
Net written premiums	497,757	434,639
Premiums earned	429,641	392,616
Incurred losses and LAE	213,455	198,158
Commission and brokerage	92,968	87,326
Other underwriting expenses	9,482	10,534
Underwriting gain (loss)	113,736	96,598
International [Member]
Segment Reporting Information [Line Items]
Gross written premiums	321,242	297,560
Net written premiums	309,037	293,982
Premiums earned	318,381	311,978
Incurred losses and LAE	163,174	161,199
Commission and brokerage	70,974	71,444
Other underwriting expenses	7,837	7,930
Underwriting gain (loss)	76,396	71,405
Bermuda [Member]
Segment Reporting Information [Line Items]
Gross written premiums	183,415	195,758
Net written premiums	182,570	195,823
Premiums earned	173,686	185,333
Incurred losses and LAE	94,508	91,996
Commission and brokerage	45,708	43,651
Other underwriting expenses	8,286	7,759
Underwriting gain (loss)	25,184	41,927
U.S Insurance [Member]
Segment Reporting Information [Line Items]
Gross written premiums	230,650	252,681
Net written premiums	211,668	225,249
Premiums earned	203,237	198,832
Incurred losses and LAE	142,191	141,291
Commission and brokerage	34,209	30,625
Other underwriting expenses	23,233	26,723
Underwriting gain (loss)	3,604	193
Mt. Logan Re [Member]
Segment Reporting Information [Line Items]
Gross written premiums	36,476
Net written premiums	26,557
Premiums earned	19,545
Incurred losses and LAE	6,081
Commission and brokerage	2,143
Other underwriting expenses	1,800
Underwriting gain (loss)	$ 9,521