Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Financial data by segment
Gross written premiums	$ 87,549	$ 82,879	$ 161,314	$ 157,224
Net written premiums	69,917	66,416	130,769	126,426
Net earned premiums	62,017	59,150	123,429	113,518
Fee & other income	729	798	1,410	1,674
Losses & loss adjustment expenses	40,819	39,869	78,100	82,129
Acquisition & other underwriting expenses	26,350	23,410	51,845	45,364
Underwriting profit (loss)	(4,423)	(3,331)	(5,106)	(12,301)
Net investment income	7,402	8,050	15,214	15,486
Pre-tax operating income (loss)	2,979	4,719	10,108	3,185
Net realized gains (loss)	(13)	194	39	11,302
Interest and corporate expenses	1,215	1,380	2,889	2,592
Earnings before income taxes	1,751	3,533	7,258	11,895
Income tax benefit	(234)	(549)	872	(581)
Net earnings	1,985	4,082	6,386	12,476
Less: Net losses attributable to the non-controlling interest	(182)	30	163	523
Net earnings attributable to American Safety Insurance Holdings, Ltd.	2,167	4,052	6,223	11,953
Loss ratio	65.80%	67.40%	63.30%	72.30%
Expense ratio	41.30%	38.20%	40.90%	38.50%
Combined ratio	107.10%	105.60%	104.20%	110.80%
E & S [Member]
Financial data by segment
Gross written premiums	50,448	43,929	89,059	79,924
Net written premiums	39,735	34,413	70,468	64,015
Net earned premiums	33,600	29,085	64,750	57,079
Fee & other income		(5)
Losses & loss adjustment expenses	20,221	17,885	39,138	35,638
Acquisition & other underwriting expenses	15,140	12,412	29,057	24,633
Underwriting profit (loss)	(1,761)	(1,217)	(3,445)	(3,192)
Net investment income	4,285	5,081	8,910	9,896
Pre-tax operating income (loss)	2,524	3,864	5,465	6,704
Loss ratio	60.20%	61.50%	60.40%	62.40%
Expense ratio	45.10%	42.70%	44.90%	43.20%
Combined ratio	105.30%	104.20%	105.30%	105.60%
ART [Member]
Financial data by segment
Gross written premiums	21,498	23,923	42,676	45,801
Net written premiums	14,579	17,140	30,722	32,046
Net earned premiums	13,157	15,616	29,501	29,971
Fee & other income	738	770	1,402	1,630
Losses & loss adjustment expenses	11,875	12,830	21,862	21,844
Acquisition & other underwriting expenses	5,865	5,916	12,253	11,964
Underwriting profit (loss)	(3,845)	(2,360)	(3,212)	(2,207)
Net investment income	1,348	1,232	2,778	2,352
Pre-tax operating income (loss)	(2,497)	(1,128)	(434)	145
Loss ratio	90.30%	82.20%	74.10%	72.90%
Expense ratio	39.00%	33.00%	36.80%	34.50%
Combined ratio	129.30%	115.20%	110.90%	107.40%
Reinsurance [Member]
Financial data by segment
Gross written premiums	15,603	15,028	29,579	31,500
Net written premiums	15,603	14,864	29,579	30,366
Net earned premiums	15,260	14,450	29,178	26,469
Losses & loss adjustment expenses	8,751	9,153	17,100	24,647
Acquisition & other underwriting expenses	4,471	4,249	8,801	7,114
Underwriting profit (loss)	2,038	1,048	3,277	(5,292)
Net investment income	1,595	1,586	3,216	2,935
Pre-tax operating income (loss)	3,633	2,634	6,493	(2,357)
Loss ratio	57.30%	63.30%	58.60%	93.10%
Expense ratio	29.30%	29.40%	30.20%	26.90%
Combined ratio	86.60%	92.70%	88.80%	120.00%
Run-off [Member]
Financial data by segment
Gross written premiums		(1)		(1)
Net written premiums		(1)		(1)
Net earned premiums		(1)		(1)
Fee & other income	(9)	33	8	44
Losses & loss adjustment expenses	(28)	1
Acquisition & other underwriting expenses	874	833	1,734	1,653
Underwriting profit (loss)	(855)	(802)	(1,726)	(1,610)
Net investment income	174	151	310	303
Pre-tax operating income (loss)	$ (681)	$ (651)	$ (1,416)	$ (1,307)