Segment Information (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Jul. 02, 2012	Dec. 31, 2011
Financial data about the geographic locations
Income tax expense	$ 1,350	$ 1,169	$ 2,222	$ 588
Net (loss) earnings attributable to American Safety Insurance Holdings, Ltd.	6,206	5,797	12,429	17,750
Assets	1,368,588	1,277,399	1,368,588	1,277,399	31,911	1,286,532
Equity	355,809	339,949	355,809	339,949		334,680
United States [Member]
Financial data about the geographic locations
Income tax expense	1,350	1,169	2,222	588
Net (loss) earnings attributable to American Safety Insurance Holdings, Ltd.	2,702	2,198	3,968	799
Assets	680,844	664,526	680,844	664,526
Equity	138,576	111,130	138,576	111,130
Bermuda [Member]
Financial data about the geographic locations
Income tax expense
Net (loss) earnings attributable to American Safety Insurance Holdings, Ltd.	3,504	3,599	8,461	16,951
Assets	687,744	612,873	687,744	612,873
Equity	$ 210,673	$ 228,819	$ 210,673	$ 228,819