Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Financial data by segment
Gross written premiums	$ 81,199	$ 73,765
Net written premiums	64,069	60,852
Net earned premiums	61,924	61,413
Fee & other income	1,240	680
Losses & loss adjustment expenses	37,964	37,281
Acquisition & other underwriting expenses	26,893	25,496
Underwriting profit (loss)	(1,693)	(684)
Net investment income	7,632	7,811
Pre-tax operating income (loss)	5,939	7,127
Net realized gains	1,454	53
Interest and corporate expenses	1,135	1,673
Earnings before income taxes	6,258	5,507
Income tax expense	677	1,106
Net earnings	5,581	4,401
Less: Net earnings attributable to the non-controlling interest	88	345
Net earnings attributable to American Safety Insurance Holdings, Ltd.	5,493	4,056
Loss ratio	61.30%	60.70%
Expense ratio	41.40%	40.40%
Combined ratio	102.70%	101.10%
E & S [Member]
Financial data by segment
Gross written premiums	47,953	38,611
Net written premiums	37,546	30,733
Net earned premiums	36,541	31,150
Fee & other income	332
Losses & loss adjustment expenses	22,028	18,917
Acquisition & other underwriting expenses	16,595	13,916
Underwriting profit (loss)	(1,750)	(1,683)
Net investment income	4,598	4,625
Pre-tax operating income (loss)	2,848	2,942
Loss ratio	60.30%	60.70%
Expense ratio	44.50%	44.70%
Combined ratio	104.80%	105.40%
ART [Member]
Financial data by segment
Gross written premiums	16,602	21,178
Net written premiums	9,879	16,143
Net earned premiums	11,162	16,344
Fee & other income	771	663
Losses & loss adjustment expenses	7,393	9,987
Acquisition & other underwriting expenses	4,830	6,388
Underwriting profit (loss)	(290)	632
Net investment income	1,230	1,429
Pre-tax operating income (loss)	940	2,061
Loss ratio	66.20%	61.10%
Expense ratio	36.40%	35.00%
Combined ratio	102.60%	96.10%
Reinsurance [Member]
Financial data by segment
Gross written premiums	16,644	13,976
Net written premiums	16,644	13,976
Net earned premiums	14,221	13,919
Fee & other income
Losses & loss adjustment expenses	8,543	8,349
Acquisition & other underwriting expenses	4,648	4,330
Underwriting profit (loss)	1,030	1,240
Net investment income	1,670	1,621
Pre-tax operating income (loss)	2,700	2,861
Loss ratio	60.10%	60.00%
Expense ratio	32.70%	31.10%
Combined ratio	92.80%	91.10%
Other Run-off [Member]
Financial data by segment
Gross written premiums
Net written premiums
Net earned premiums
Fee & other income	137	17
Losses & loss adjustment expenses		28
Acquisition & other underwriting expenses	820	862
Underwriting profit (loss)	(683)	(873)
Net investment income	134	136
Pre-tax operating income (loss)	$ (549)	$ (737)