Financial Data by Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Segment Reporting Information [Line Items]
Gross written premiums	$ 396,460		$ 422,790
Ceded written premiums	(107,502)		(110,940)
Net written premiums	288,958		311,850
Net earned premiums	236,132		225,272
Net losses and LAE	(130,198)		(135,067)
Commission expenses	(32,905)		(25,727)
Other operating expenses	(54,909)		(47,146)
Other underwriting income (expense)	55		155
Underwriting profit (loss)	18,175		17,487
Net investment income	16,253		16,610
Net realized gains (losses)	5,596		833
Interest expense	(3,855)		(3,852)
Other income	2,187		10,244
Income before income taxes	38,356		41,322
Income tax (expense) benefit	(12,427)		(13,354)
Net income (loss)	25,929		27,968
Losses and LAE ratio	55.10%		60.00%
Commission expense ratio	13.90%		11.40%
Other operating expense ratio	23.30%	[1]	20.80%	[1]
Combined ratio	92.30%		92.20%
U.S.Insurance
Segment Reporting Information [Line Items]
Gross written premiums	199,327		198,348
Ceded written premiums	(68,730)		(65,066)
Net written premiums	130,597		133,282
Net earned premiums	131,091		115,190
Net losses and LAE	(77,799)		(72,964)
Commission expenses	(14,345)		(9,509)
Other operating expenses	(33,688)		(27,993)
Other underwriting income (expense)	196		513
Underwriting profit (loss)	5,455		5,237
Income before income taxes	5,455		5,237
Losses and LAE ratio	59.30%		63.30%
Commission expense ratio	10.90%		8.30%
Other operating expense ratio	25.60%	[1]	23.90%	[1]
Combined ratio	95.80%		95.50%
International Insurance
Segment Reporting Information [Line Items]
Gross written premiums	122,427		119,192
Ceded written premiums	(34,256)		(42,582)
Net written premiums	88,171		76,610
Net earned premiums	65,525		62,054
Net losses and LAE	(29,691)		(31,220)
Commission expenses	(11,413)		(8,855)
Other operating expenses	(17,009)		(15,059)
Other underwriting income (expense)			6
Underwriting profit (loss)	7,412		6,926
Income before income taxes	7,412		6,926
Losses and LAE ratio	45.30%		50.30%
Commission expense ratio	17.40%		14.30%
Other operating expense ratio	26.00%	[1]	24.20%	[1]
Combined ratio	88.70%		88.80%
Global Reinsurance
Segment Reporting Information [Line Items]
Gross written premiums	74,706		105,250
Ceded written premiums	(4,516)		(3,292)
Net written premiums	70,190		101,958
Net earned premiums	39,516		48,028
Net losses and LAE	(22,708)		(30,883)
Commission expenses	(7,298)		(7,872)
Other operating expenses	(4,212)		(4,094)
Other underwriting income (expense)	10		145
Underwriting profit (loss)	5,308		5,324
Income before income taxes	5,308		5,324
Losses and LAE ratio	57.50%		64.30%
Commission expense ratio	18.50%		16.40%
Other operating expense ratio	10.60%	[1]	8.20%	[1]
Combined ratio	86.60%		88.90%
Corporate
Segment Reporting Information [Line Items]
Commission expenses	151	[2]	509	[2]
Other underwriting income (expense)	(151)	[2]	(509)	[2]
Net investment income	16,253	[2]	16,610	[2]
Net realized gains (losses)	5,596	[2]	833	[2]
Interest expense	(3,855)	[2]	(3,852)	[2]
Other income	2,187	[2]	10,244	[2]
Income before income taxes	20,181	[2]	23,835	[2]
Income tax (expense) benefit	$ (12,427)	[2]	$ (13,354)	[2]

[1] Includes Other operating expenses and Other underwriting income.

[2] Includes Corporate segment intercompany eliminations.