Segment Results (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010		Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Segment Reporting Information [Line Items]
Gross written premiums	$ 277,901		$ 255,318	$ 278,714	$ 296,283	$ 229,850		$ 233,638	$ 253,568	$ 270,145	$ 1,108,216		$ 987,201		$ 1,044,918
Net written premiums	202,002		175,357	183,363	193,076	141,809		157,807	165,005	189,317	753,798		653,938		701,255
Net earned premiums	191,757		173,633	173,777	152,478	166,158		168,233	161,471	164,069	691,645		659,931		683,363
Net losses and loss adjustment expenses	(136,104)		(110,242)	(113,863)	(116,788)	(110,022)		(107,463)	(99,863)	(103,807)	(476,997)		(421,155)		(435,998)
Commission expenses	(30,273)		(25,934)	(28,030)	(26,200)	(32,935)		(25,185)	(25,677)	(25,316)	(110,437)		(109,113)		(98,908)
Other operating expenses											(138,029)		(139,743)		(132,697)
Other income (expense)											1,229		5,186		3,691
Underwriting profit (loss)											(32,589)		(4,894)		19,451
Net investment income	12,428		16,259	17,429	17,384	17,998		17,839	17,853	17,972	63,500		71,662		75,512
Net realized gains (losses)											10,011		40,239		(2,660)
Gain on debt repurchase															3,000
Interest expense	(2,048)		(2,047)	(2,047)	(2,046)	(2,045)		(2,045)	(2,044)	(2,044)	(8,188)		(8,178)		(8,455)
Income (loss) before income taxes	12,210		18,374	14,536	(12,386)	24,930		23,316	27,193	23,390	32,734		98,829		86,848
Income tax expense (benefit)	2,122		4,476	5,032	(4,493)	7,592		7,091	8,223	6,345	7,137		29,251		23,690
Net income (loss)	10,088		13,898	9,504	(7,893)	17,338		16,225	18,970	17,045	25,597		69,578		63,158
Identifiable assets	3,670,007					3,531,459					3,670,007		3,531,459		3,453,994
Losses and loss adjustment expenses ratio											69.00%		63.80%		63.80%
Commission expense ratio											16.00%		16.50%		14.50%
Other operating expense ratio											19.70%	[1]	20.40%	[1]	18.90%	[1]
Combined ratio	102.50%		99.10%	101.90%	117.10%	106.30%		97.80%	99.70%	99.10%	104.70%		100.70%		97.20%
Insurance Companies
Segment Reporting Information [Line Items]
Gross written premiums											788,419		665,505		730,776
Net written premiums											542,391		429,355		477,673
Net earned premiums											472,463		438,851		479,121
Net losses and loss adjustment expenses											(341,625)		(280,120)		(304,672)
Commission expenses											(64,165)		(59,122)		(61,949)
Other operating expenses											(101,517)		(106,631)		(104,801)
Other income (expense)											3,955		1,698		3,498
Underwriting profit (loss)											(30,889)		(5,324)		11,197
Net investment income											54,164		62,792		65,717
Net realized gains (losses)											12,151		36,057		533
Income (loss) before income taxes											35,426		93,525		77,447
Income tax expense (benefit)											8,271		27,219		19,819
Net income (loss)											27,155		66,306		57,628
Identifiable assets	2,768,930					2,623,871					2,768,930		2,623,871		2,576,643
Losses and loss adjustment expenses ratio											72.30%		63.80%		63.60%
Commission expense ratio											13.60%		13.50%		12.90%
Other operating expense ratio											20.60%	[1]	23.90%	[1]	21.10%	[1]
Combined ratio											106.50%		101.20%		97.60%
Lloyd's Operations
Segment Reporting Information [Line Items]
Gross written premiums											319,797		321,696		314,142
Net written premiums											211,407		224,583		223,582
Net earned premiums											219,182		221,080		204,242
Net losses and loss adjustment expenses											(135,372)		(141,035)		(131,326)
Commission expenses											(48,341)		(49,991)		(37,727)
Other operating expenses											(36,512)		(33,112)		(27,896)
Other income (expense)											(657)		3,488		961
Underwriting profit (loss)											(1,700)		430		8,254
Net investment income											8,955		8,286		9,229
Net realized gains (losses)											(2,354)		3,323		(3,193)
Income (loss) before income taxes											4,901		12,039		14,290
Income tax expense (benefit)											1,523		4,389		5,582
Net income (loss)											3,378		7,650		8,708
Identifiable assets	865,230					838,047					865,230		838,047		791,143
Losses and loss adjustment expenses ratio											61.80%		63.80%		64.30%
Commission expense ratio											22.10%		22.60%		18.50%
Other operating expense ratio											16.90%	[1]	13.40%	[1]	13.20%	[1]
Combined ratio											100.80%		99.80%		96.00%
Corporate
Segment Reporting Information [Line Items]
Commission expenses											2,069	[2]			768	[2]
Other income (expense)											(2,069)	[2]			(768)	[2]
Net investment income											381	[2]	584	[2]	566	[2]
Net realized gains (losses)											214	[2]	859	[2]
Gain on debt repurchase															3,000	[2]
Interest expense											(8,188)	[2]	(8,178)	[2]	(8,455)	[2]
Income (loss) before income taxes											(7,593)	[2]	(6,735)	[2]	(4,889)	[2]
Income tax expense (benefit)											(2,657)	[2]	(2,357)	[2]	(1,711)	[2]
Net income (loss)											(4,936)	[2]	(4,378)	[2]	(3,178)	[2]
Identifiable assets	$ 35,847	[2]				$ 69,541	[2]				$ 35,847	[2]	$ 69,541	[2]	$ 86,208	[2]

[1] Includes Other operating expenses and Other income.

[2] Includes Corporate segment intercompany eliminations.