Income Before Income Taxes From its Non-U.S. Subsidiaries and U.S. Subsidiaries (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Revenues:
Gross premiums written	$ 67,632	$ 94,962	$ 125,390	$ 182,628
Net premiums written	61,135	86,407	111,416	169,515
Net premiums earned	57,859	78,055	122,329	154,024
Net investment income	11,071	13,930	22,488	28,344
Net realized investment gains	1,941	8,386	3,702	20,383
Other income	(40)	375	(392)	12,167
Total revenues	70,831	100,746	148,127	214,918
Losses and Expenses:
Net losses and loss adjustment expenses	36,158	61,753	78,167	120,095
Acquisition costs and other underwriting expenses	23,760	30,089	46,927	59,483
Corporate and other operating expenses	2,336	4,899	4,824	7,802
Interest expense	1,470	1,743	2,948	3,495
Income (loss) before income taxes	7,107	2,262	15,261	24,043
Non-U.S. Subsidiaries
Revenues:
Gross premiums written	39,177	56,758	70,588	115,455
Net premiums written	39,177	56,758	70,040	114,953
Net premiums earned	37,086	50,837	78,841	100,463
Net investment income	9,271	11,297	19,059	22,946
Net realized investment gains	539	2,371	331	5,786
Other income	(199)	212	(705)	335
Total revenues	46,697	64,717	97,526	129,530
Losses and Expenses:
Net losses and loss adjustment expenses	23,239	38,685	50,283	79,536
Acquisition costs and other underwriting expenses	14,126	20,013	29,575	38,750
Corporate and other operating expenses	1,764	3,687	4,385	5,450
Income (loss) before income taxes	7,568	2,332	13,283	5,794
U.S. Subsidiaries
Revenues:
Gross premiums written	52,371	70,375	100,205	126,842
Net premiums written	21,958	29,649	41,376	54,562
Net premiums earned	20,773	27,218	43,488	53,561
Net investment income	6,385	7,230	12,599	14,543
Net realized investment gains	1,402	6,015	3,371	14,597
Other income	159	163	313	11,832
Total revenues	28,719	40,626	59,771	94,533
Losses and Expenses:
Net losses and loss adjustment expenses	12,919	23,068	27,884	40,559
Acquisition costs and other underwriting expenses	9,634	10,076	17,352	20,733
Corporate and other operating expenses	572	1,212	439	2,352
Interest expense	6,055	6,340	12,118	12,640
Income (loss) before income taxes	(461)	(70)	1,978	18,249
Eliminations
Revenues:
Gross premiums written	(23,916)	(32,171)	(45,403)	(59,669)
Net investment income	(4,585)	(4,597)	(9,170)	(9,145)
Total revenues	(4,585)	(4,597)	(9,170)	(9,145)
Losses and Expenses:
Interest expense	$ (4,585)	$ (4,597)	$ (9,170)	$ (9,145)