Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Financial data by segment
Gross written premiums	$ 83,860	$ 87,549	$ 165,059	$ 161,314
Net written premiums	60,310	69,917	124,379	130,769
Net earned premiums	62,192	62,017	124,116	123,429
Fee & other income	347	729	1,587	1,410
Losses & loss adjustment expenses	37,673	40,819	75,636	78,100
Acquisition & other underwriting expenses	26,196	26,350	53,091	51,845
Underwriting profit (loss)	(1,330)	(4,423)	(3,024)	(5,106)
Net investment income	5,582	7,402	13,214	15,214
Pre-tax operating income (loss)	4,252	2,979	10,190	10,108
Net realized gains	37,482	(13)	38,936	39
Interest and corporate expenses	1,013	1,215	2,148	2,889
Earnings before income taxes	40,721	1,751	46,978	7,258
Income tax expense	5,900	(234)	6,577	872
Net earnings	34,821	1,985	40,401	6,386
Less: Net earnings (loss) attributable to the non-controlling interest	10	(182)	98	163
Net earnings attributable to American Safety Insurance Holdings, Ltd.	34,811	2,167	40,303	6,223
Loss ratio	60.60%	65.80%	60.90%	63.30%
Expense ratio	41.60%	41.30%	41.50%	40.90%
Combined ratio	102.20%	107.10%	102.40%	104.20%
E & S [Member]
Financial data by segment
Gross written premiums	52,063	50,448	100,016	89,059
Net written premiums	41,669	39,735	79,215	70,468
Net earned premiums	38,844	33,600	75,385	64,750
Fee & other income	(362)		(30)
Losses & loss adjustment expenses	23,317	20,221	45,344	39,138
Acquisition & other underwriting expenses	17,275	15,140	33,871	29,057
Underwriting profit (loss)	(2,110)	(1,761)	(3,860)	(3,445)
Net investment income	3,380	4,285	7,978	8,910
Pre-tax operating income (loss)	1,270	2,524	4,118	5,465
Loss ratio	60.00%	60.20%	60.10%	60.40%
Expense ratio	45.40%	45.10%	45.00%	44.90%
Combined ratio	105.40%	105.30%	105.10%	105.30%
ART [Member]
Financial data by segment
Gross written premiums	16,156	21,498	32,758	42,676
Net written premiums	3,000	14,579	12,879	30,722
Net earned premiums	8,093	13,157	19,255	29,501
Fee & other income	697	738	1,468	1,402
Losses & loss adjustment expenses	5,226	11,875	12,619	21,862
Acquisition & other underwriting expenses	3,528	5,865	8,358	12,253
Underwriting profit (loss)	36	(3,845)	(254)	(3,212)
Net investment income	815	1,348	2,045	2,778
Pre-tax operating income (loss)	851	(2,497)	1,791	(434)
Loss ratio	64.60%	90.30%	65.50%	74.10%
Expense ratio	35.00%	39.00%	35.80%	36.80%
Combined ratio	99.60%	129.30%	101.30%	110.90%
Reinsurance [Member]
Financial data by segment
Gross written premiums	15,641	15,603	32,285	29,579
Net written premiums	15,641	15,603	32,285	29,579
Net earned premiums	15,255	15,260	29,476	29,178
Fee & other income
Losses & loss adjustment expenses	9,130	8,751	17,673	17,100
Acquisition & other underwriting expenses	4,623	4,471	9,272	8,801
Underwriting profit (loss)	1,502	2,038	2,531	3,277
Net investment income	1,304	1,595	2,974	3,216
Pre-tax operating income (loss)	2,806	3,633	5,505	6,493
Loss ratio	59.80%	57.30%	60.00%	58.60%
Expense ratio	30.30%	29.30%	31.50%	30.20%
Combined ratio	90.10%	86.60%	91.50%	88.80%
Other Run-off [Member]
Financial data by segment
Gross written premiums
Net written premiums
Net earned premiums
Fee & other income	12	(9)	149	8
Losses & loss adjustment expenses		(28)
Acquisition & other underwriting expenses	770	874	1,590	1,734
Underwriting profit (loss)	(758)	(855)	(1,441)	(1,726)
Net investment income	83	174	217	310
Pre-tax operating income (loss)	$ (675)	$ (681)	$ (1,224)	$ (1,416)