Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
ASSETS:
Investments	$ 8,179,810		$ 7,868,682
Cash and cash equivalents	603,810		589,339	$ 831,270		$ 531,936
Insurance balances receivable	905,401		664,815
Funds held	443,670		724,021
Reinsurance recoverable	1,449,832	$ 1,433,109	1,340,256	1,349,009	$ 1,301,742	1,234,504
Reinsurance recoverable on paid losses	117,110		86,075
Net deferred acquisition costs	201,313		151,546
Goodwill and intangible assets	485,393		324,556
Balances receivable on sale of investments	29,461		47,149
Investments in subsidiaries	0		0
Due from subsidiaries	0		0
Other assets	781,779		625,124
Total assets	13,197,579		12,421,563
LIABILITIES:
Reserve for losses and loss expenses	6,436,579	$ 6,363,948	5,881,165	6,052,263	$ 5,935,678	5,766,529
Unearned premiums	1,835,527		1,555,313
Reinsurance balances payable	260,225		180,060
Balances due on purchases of investments	108,337		5,428
Senior notes	799,043		798,802
Other long-term debt	23,328		19,213
Due to subsidiaries	0		0
Other liabilities	179,135		203,291
Total liabilities	9,642,174		8,643,272
Total shareholders’ equity	3,555,405		3,778,291	3,673,599		3,519,826
Total liabilities and shareholders’ equity	$ 13,197,579		12,421,563
Percentage ownership of Subsidiary Issuer	100.00%
Consolidation, Eliminations [Member]
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		0
Net deferred acquisition costs	0		0
Goodwill and intangible assets	0		0
Balances receivable on sale of investments	0		0
Investments in subsidiaries	(7,219,643)		(7,847,329)
Due from subsidiaries	(276,097)		(180,658)
Other assets	0		0
Total assets	(7,495,740)		(8,027,987)
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		0
Due to subsidiaries	(276,097)		(180,658)
Other liabilities	0		0
Total liabilities	(276,097)		(180,658)
Total shareholders’ equity	(7,219,643)		(7,847,329)
Total liabilities and shareholders’ equity	(7,495,740)		(8,027,987)
Allied World Switzerland (Parent Guarantor) [Member]
ASSETS:
Investments	0		0
Cash and cash equivalents	30,561		32,579	38,196		10,790
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	3,337,480		3,629,301
Due from subsidiaries	216,992		147,072
Other assets	2,402		1,470
Total assets	3,587,435		3,810,422
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		0
Due to subsidiaries	6,559		7,599
Other liabilities	25,471		24,532
Total liabilities	32,030		32,131
Total shareholders’ equity	3,555,405		3,778,291
Total liabilities and shareholders’ equity	3,587,435		3,810,422
Allied World Bermuda (Subsidiary Issuer) [Member]
ASSETS:
Investments	0		0
Cash and cash equivalents	1,462		1,734	2,329		2,775
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	3,882,163		4,218,028
Due from subsidiaries	45,005		19,190
Other assets	2,298		3,192
Total assets	3,930,928		4,242,144
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	799,043		798,802
Other long-term debt	0		0
Due to subsidiaries	7,541		6,797
Other liabilities	12,477		19,618
Total liabilities	819,061		825,217
Total shareholders’ equity	3,111,867		3,416,927
Total liabilities and shareholders’ equity	3,930,928		4,242,144
Other Allied World Subsidiaries [Member]
ASSETS:
Investments	8,179,810		7,868,682
Cash and cash equivalents	571,787		555,026	$ 790,745		$ 518,371
Insurance balances receivable	905,401		664,815
Funds held	443,670		724,021
Reinsurance recoverable	1,449,832		1,340,256
Reinsurance recoverable on paid losses	117,110		86,075
Net deferred acquisition costs	201,313		151,546
Goodwill and intangible assets	485,393		324,556
Balances receivable on sale of investments	29,461		47,149
Investments in subsidiaries	0		0
Due from subsidiaries	14,100		14,396
Other assets	777,079		620,462
Total assets	13,174,956		12,396,984
LIABILITIES:
Reserve for losses and loss expenses	6,436,579		5,881,165
Unearned premiums	1,835,527		1,555,313
Reinsurance balances payable	260,225		180,060
Balances due on purchases of investments	108,337		5,428
Senior notes	0		0
Other long-term debt	23,328		19,213
Due to subsidiaries	261,997		166,262
Other liabilities	141,187		159,141
Total liabilities	9,067,180		7,966,582
Total shareholders’ equity	4,107,776		4,430,402
Total liabilities and shareholders’ equity	$ 13,174,956		$ 12,396,984