Subsequent events	9 Months Ended
Sep. 30, 2012
Subsequent Events [Abstract]
Subsequent events	15. SUBSEQUENT EVENTS On October 9, 2012, the Company announced plans to expand its asset management business through a strategic partnership between MatlinPatterson Asset Management L.P. (“MatlinPatterson”) and Allied World Financial Services, Ltd (a subsidiary of the Company that was formed in the third quarter 2012 to expand our asset management expertise, invest in strategic business opportunities and diversify the Company's earnings stream with business relationships that complement the Company's core property and casualty business). Under the terms of the transaction, the Company will become a minority owner of MatlinPatterson and will provide growth capital for the continued expansion of their asset management platform. Additionally, MatlinPatterson will manage $500 million of the Company's investment portfolio, over time, in existing and future liquid credit strategies. In late October, Hurricane Sandy impacted the Mid-Atlantic and Northeast coasts of the United States, ultimately making landfall in New Jersey, with tropical storm force or greater winds. In addition, Hurricane Sandy generated significant storm surge, which contributed to widespread power outages, significant disruptions to travel and devastating flooding throughout a number of states, including New York and New Jersey. The Company is currently assessing its potential claims related to this event, but information as of this filing is not sufficient to arrive at a reasonable estimate.

Subsequent events

9 Months Ended

Sep. 30, 2012

15. SUBSEQUENT EVENTS

On October 9, 2012, the Company announced plans to expand its asset management business through a strategic partnership between MatlinPatterson Asset Management L.P. (“MatlinPatterson”) and Allied World Financial Services, Ltd (a subsidiary of the Company that was formed in the third quarter 2012 to expand our asset management expertise, invest in strategic business opportunities and diversify the Company's earnings stream with business relationships that complement the Company's core property and casualty business). Under the terms of the transaction, the Company will become a minority owner of MatlinPatterson and will provide growth capital for the continued expansion of their asset management platform. Additionally, MatlinPatterson will manage $500 million of the Company's investment portfolio, over time, in existing and future liquid credit strategies.

In late October, Hurricane Sandy impacted the Mid-Atlantic and Northeast coasts of the United States, ultimately making landfall in New Jersey, with tropical storm force or greater winds. In addition, Hurricane Sandy generated significant storm surge, which contributed to widespread power outages, significant disruptions to travel and devastating flooding throughout a number of states, including New York and New Jersey. The Company is currently assessing its potential claims related to this event, but information as of this filing is not sufficient to arrive at a reasonable estimate.