Schedule IV - Reinsurance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Amount	$ 6,412,533	$ 6,185,242	$ 5,626,172
Ceded to Other Companies	1,060,478	1,065,891	1,010,918
Assumed from Other Companies	837,460	877,596	884,919
Total net premiums written	$ 6,189,515	$ 5,996,947	$ 5,500,173
Percentage of Amount Assumed to Net	13.50%	14.60%	16.10%
Insurance-Domestic
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Amount	$ 5,521,447	$ 5,214,849	$ 4,699,348
Ceded to Other Companies	871,358	866,092	809,368
Assumed from Other Companies	162,741	168,830	104,407
Total net premiums written	$ 4,812,830	$ 4,517,587	$ 3,994,387
Percentage of Amount Assumed to Net	3.40%	3.70%	2.60%
Insurance-International
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Amount	$ 874,359	$ 927,799	$ 887,027
Ceded to Other Companies	144,737	156,195	142,591
Assumed from Other Companies	48,945	56,472	11,749
Total net premiums written	$ 778,567	$ 828,076	$ 756,185
Percentage of Amount Assumed to Net	6.30%	6.80%	1.60%
Reinsurance-Global
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct Amount	$ 16,727	$ 42,594	$ 39,797
Ceded to Other Companies	44,383	43,604	58,959
Assumed from Other Companies	625,774	652,294	768,763
Total net premiums written	$ 598,118	$ 651,284	$ 749,601
Percentage of Amount Assumed to Net	104.60%	100.20%	102.60%