Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Financial data by segment
Gross written premiums	$ 79,145	$ 73,246	$ 240,459	$ 230,470
Net written premiums	61,582	60,220	192,351	186,646
Net earned premiums	63,095	58,992	186,524	172,511
Fee & other income	1,263	855	2,673	2,529
Losses & loss adjustment expenses	40,289	35,867	118,389	117,997
Acquisition & other underwriting expenses	28,367	24,628	80,211	69,992
Underwriting profit (loss)	(4,298)	(648)	(9,403)	(12,949)
Net investment income	7,364	8,196	22,577	23,682
Pre-tax operating income (loss)	3,066	7,548	13,174	10,733
Net realized gains	5,693	10	5,732	11,311
Interest and corporate expenses	1,331	661	4,220	3,252
Earnings before income taxes	7,428	6,897	14,686	18,792
Income tax expense	1,350	1,169	2,222	588
Net earnings	6,078	5,728	12,464	18,204
Less: Net losses attributable to the non-controlling interest	(128)	(69)	35	454
Net earnings attributable to ASIH, Ltd.	6,206	5,797	12,429	17,750
Loss ratio	63.90%	60.80%	63.50%	68.40%
Expense ratio	43.00%	40.30%	41.60%	39.10%
Combined ratio	106.90%	101.10%	105.10%	107.50%
E & S [Member]
Financial data by segment
Gross written premiums	49,192	39,782	138,251	119,706
Net written premiums	39,004	31,621	109,472	95,636
Net earned premiums	35,650	30,752	100,400	87,831
Fee & other income	294	(8)	294	(8)
Losses & loss adjustment expenses	20,979	19,019	60,117	54,657
Acquisition & other underwriting expenses	16,812	12,778	45,869	37,411
Underwriting profit (loss)	(1,847)	(1,053)	(5,292)	(4,245)
Net investment income	4,452	5,280	13,362	15,176
Pre-tax operating income (loss)	2,605	4,227	8,070	10,931
Net realized gains
Interest and corporate expenses
Earnings before income taxes
Income tax expense
Net earnings
Less: Net losses attributable to the non-controlling interest
Net earnings attributable to ASIH, Ltd.
Loss ratio	58.80%	61.80%	59.90%	62.20%
Expense ratio	46.30%	41.60%	45.40%	42.60%
Combined ratio	105.20%	103.40%	105.30%	104.80%
ART [Member]
Financial data by segment
Gross written premiums	16,146	18,952	58,822	64,753
Net written premiums	8,772	14,040	39,494	46,086
Net earned premiums	13,295	15,552	42,796	45,523
Fee & other income	915	806	2,317	2,436
Losses & loss adjustment expenses	10,423	8,466	32,285	30,310
Acquisition & other underwriting expenses	6,280	6,464	18,533	18,428
Underwriting profit (loss)	(2,493)	1,428	(5,705)	(779)
Net investment income	1,030	1,186	3,807	3,538
Pre-tax operating income (loss)	(1,463)	2,614	(1,898)	2,759
Net realized gains
Interest and corporate expenses
Earnings before income taxes
Income tax expense
Net earnings
Less: Net losses attributable to the non-controlling interest
Net earnings attributable to ASIH, Ltd.
Loss ratio	78.40%	54.40%	75.40%	66.60%
Expense ratio	40.40%	36.40%	37.90%	35.10%
Combined ratio	118.80%	90.80%	113.30%	101.70%
Reinsurance [Member]
Financial data by segment
Gross written premiums	13,807	14,512	43,386	46,012
Net written premiums	13,806	14,559	43,385	44,925
Net earned premiums	14,150	12,688	43,328	39,158
Fee & other income
Losses & loss adjustment expenses	8,887	8,382	25,987	33,030
Acquisition & other underwriting expenses	4,303	4,491	13,104	11,605
Underwriting profit (loss)	960	(185)	4,237	(5,477)
Net investment income	1,745	1,593	4,961	4,528
Pre-tax operating income (loss)	2,705	1,408	9,198	(949)
Net realized gains
Interest and corporate expenses
Earnings before income taxes
Income tax expense
Net earnings
Less: Net losses attributable to the non-controlling interest
Net earnings attributable to ASIH, Ltd.
Loss ratio	62.80%	66.10%	60.00%	84.40%
Expense ratio	30.40%	35.40%	30.20%	29.60%
Combined ratio	93.20%	101.50%	90.20%	114.00%
Run-off [Member]
Financial data by segment
Gross written premiums				(1)
Net written premiums				(1)
Net earned premiums				(1)
Fee & other income	54	57	62	101
Losses & loss adjustment expenses
Acquisition & other underwriting expenses	972	895	2,705	2,548
Underwriting profit (loss)	(918)	(838)	(2,643)	(2,448)
Net investment income	137	137	447	440
Pre-tax operating income (loss)	(781)	(701)	(2,196)	(2,008)
Net realized gains
Interest and corporate expenses
Earnings before income taxes
Income tax expense
Net earnings
Less: Net losses attributable to the non-controlling interest
Net earnings attributable to ASIH, Ltd.