Schedule IV - Reinsurance (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Amount	$ 5,626,172	$ 4,964,069	$ 4,370,092
Ceded to Other Companies	1,010,918	881,340	719,945
Assumed from Other Companies	884,919	815,810	707,221
Total net premiums written	5,500,173	4,898,539	4,357,368
Percentage of Amount Assumed to Net	16.10%	16.70%	16.30%
Insurance-Domestic
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Amount	4,699,348	4,133,960	3,664,780
Ceded to Other Companies	809,368	691,284	556,743
Assumed from Other Companies	104,407	127,207	130,083
Total net premiums written	3,994,387	3,569,883	3,238,120
Percentage of Amount Assumed to Net	2.60%	3.60%	4.10%
Insurance-International
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Amount	887,027	798,750	681,423
Ceded to Other Companies	142,591	137,598	129,513
Assumed from Other Companies	11,749	3,307	0
Total net premiums written	756,185	664,459	551,910
Percentage of Amount Assumed to Net	1.60%	0.50%	0.00%
Reinsurance-Global
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Amount	39,797	31,359	23,889
Ceded to Other Companies	58,959	52,458	33,689
Assumed from Other Companies	768,763	685,296	577,138
Total net premiums written	$ 749,601	$ 664,197	$ 567,338
Percentage of Amount Assumed to Net	102.60%	103.20%	101.70%