Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Balance Sheet) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
ASSETS:
Investments	$ 7,868,682	$ 7,712,036
Cash and cash equivalents	589,339	531,936	681,879	633,996	633,996
Insurance balances receivable	664,815	588,632
Funds held	724,021	632,430
Reinsurance recoverable	1,340,256	1,234,504	1,141,110	1,002,919
Reinsurance recoverable on paid losses	86,075	76,099
Net deferred acquisition costs	151,546	126,661
Goodwill and intangible assets	324,556	317,207
Balances receivable on sale of investments	47,149	76,544
Investments in subsidiaries	0	0
Due from subsidiaries	0	0
Other assets	625,124	649,781
Total assets	12,421,563	11,945,830
LIABILITIES:
Reserve for losses and loss expenses	5,881,165	5,766,529	5,645,549	5,225,143
Unearned premiums	1,555,313	1,396,256
Reinsurance balances payable	180,060	173,023
Balances due on purchases of investments	5,428	104,740
Senior notes	798,802	798,499
Other long-term debt	19,213	0
Due to subsidiaries	0	0
Other liabilities	203,291	186,957
Total liabilities	8,643,272	8,426,004
Total shareholders' equity	3,778,291	3,519,826	3,326,335	3,149,022
Total liabilities and shareholders' equity	12,421,563	11,945,830
Consolidating Adjustments
ASSETS:
Investments	0	0
Cash and cash equivalents	0	0	0	0
Insurance balances receivable	0	0
Funds held	0	0
Reinsurance recoverable	0	0
Reinsurance recoverable on paid losses		0
Net deferred acquisition costs	0	0
Goodwill and intangible assets	0	0
Balances receivable on sale of investments	0	0
Investments in subsidiaries	(7,847,329)	(7,431,620)
Due from subsidiaries	(180,658)	(357,497)
Other assets	0	0
Total assets	(8,027,987)	(7,789,117)
LIABILITIES:
Reserve for losses and loss expenses	0	0
Unearned premiums	0	0
Reinsurance balances payable	0	0
Balances due on purchases of investments	0	0
Senior notes	0	0
Other long-term debt	0
Due to subsidiaries	(180,658)	(357,497)
Other liabilities	0	0
Total liabilities	(180,658)	(357,497)
Total shareholders' equity	(7,847,329)	(7,431,620)
Total liabilities and shareholders' equity	(8,027,987)	(7,789,117)
Allied World Switzerland (Parent Guarantor)
ASSETS:
Investments	0	0
Cash and cash equivalents	32,579	10,790	19,997	112,672
Insurance balances receivable	0	0
Funds held	0	0
Reinsurance recoverable	0	0
Reinsurance recoverable on paid losses	0	0
Net deferred acquisition costs	0	0
Goodwill and intangible assets	0	0
Balances receivable on sale of investments	0	0
Investments in subsidiaries	3,629,301	3,413,001
Due from subsidiaries	147,072	111,172
Other assets	1,470	1,757
Total assets	3,810,422	3,536,720
LIABILITIES:
Reserve for losses and loss expenses	0	0
Unearned premiums	0	0
Reinsurance balances payable	0	0
Balances due on purchases of investments	0	0
Senior notes	0	0
Other long-term debt	0
Due to subsidiaries	7,599	12,945
Other liabilities	24,532	3,949
Total liabilities	32,131	16,894
Total shareholders' equity	3,778,291	3,519,826
Total liabilities and shareholders' equity	3,810,422	3,536,720
Allied World Bermuda (Subsidiary Issuer)
ASSETS:
Investments	0	0
Cash and cash equivalents	1,734	2,775	11,324	8,886
Insurance balances receivable	0	0
Funds held	0	0
Reinsurance recoverable	0	0
Reinsurance recoverable on paid losses	0	0
Net deferred acquisition costs	0	0
Goodwill and intangible assets	0	0
Balances receivable on sale of investments	0	0
Investments in subsidiaries	4,218,028	4,018,619
Due from subsidiaries	19,190	122,846
Other assets	3,192	4,671
Total assets	4,242,144	4,148,911
LIABILITIES:
Reserve for losses and loss expenses	0	0
Unearned premiums	0	0
Reinsurance balances payable	0	0
Balances due on purchases of investments		0
Senior notes	798,802	798,499
Other long-term debt	0
Due to subsidiaries	6,797	110,534
Other liabilities	19,618	17,797
Total liabilities	825,217	926,830
Total shareholders' equity	3,416,927	3,222,081
Total liabilities and shareholders' equity	4,242,144	4,148,911
Other Allied World Subsidiaries
ASSETS:
Investments	7,868,682	7,712,036
Cash and cash equivalents	555,026	518,371	650,558	512,438
Insurance balances receivable	664,815	588,632
Funds held	724,021	632,430
Reinsurance recoverable	1,340,256	1,234,504
Reinsurance recoverable on paid losses	86,075	76,099
Net deferred acquisition costs	151,546	126,661
Goodwill and intangible assets	324,556	317,207
Balances receivable on sale of investments	47,149	76,544
Investments in subsidiaries	0	0
Due from subsidiaries	14,396	123,479
Other assets	620,462	643,353
Total assets	12,396,984	12,049,316
LIABILITIES:
Reserve for losses and loss expenses	5,881,165	5,766,529
Unearned premiums	1,555,313	1,396,256
Reinsurance balances payable	180,060	173,023
Balances due on purchases of investments	5,428	104,740
Senior notes	0	0
Other long-term debt	19,213
Due to subsidiaries	166,262	234,018
Other liabilities	159,141	165,211
Total liabilities	7,966,582	7,839,777
Total shareholders' equity	4,430,402	4,209,539
Total liabilities and shareholders' equity	$ 12,396,984	$ 12,049,316