Financial Data by Segment (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Net earned premiums		$ 254,082	$ 245,367	$ 732,542	$ 701,723
Net losses and LAE		(146,546)	(135,284)	(418,717)	(410,571)
Commission expenses		(34,253)	(33,943)	(98,638)	(91,820)
Other operating expenses		(56,599)	(50,388)	(164,297)	(145,526)
Other underwriting income (expense)		19	107	99	497
Underwriting profit (loss)		16,703	25,859	50,989	54,303
Net investment income		17,371	15,839	50,219	48,097
Net realized gains (losses)		(757)	6,718	8,755	12,024
Interest expense		(3,856)	(3,388)	(11,567)	(11,559)
Other income (loss)		(2,537)	1,229	(4,737)	9,573
Income before income taxes		26,924	46,257	93,659	112,438
Income tax (expense) benefit		(8,723)	(15,032)	(30,345)	(36,384)
Net income (loss)		$ 18,201	$ 31,225	$ 63,314	$ 76,054
Losses and LAE ratio		57.70%	55.10%	57.20%	58.50%
Commission expense ratio		13.50%	13.80%	13.50%	13.10%
Other operating expense ratio	[1]	22.20%	20.60%	22.30%	20.70%
Combined ratio		93.40%	89.50%	93.00%	92.30%
U.S.Insurance
Segment Reporting Information [Line Items]
Net earned premiums		$ 142,409	$ 130,420	$ 410,804	$ 370,864
Net losses and LAE		(85,140)	(80,722)	(247,094)	(226,817)
Commission expenses		(15,157)	(12,870)	(41,777)	(35,598)
Other operating expenses		(32,948)	(29,160)	(98,010)	(85,993)
Other underwriting income (expense)		1,013	534	1,330	1,783
Underwriting profit (loss)		10,177	8,202	25,253	24,239
Income before income taxes		$ 10,177	$ 8,202	$ 25,253	$ 24,239
Losses and LAE ratio		59.80%	61.90%	60.10%	61.20%
Commission expense ratio		10.60%	9.90%	10.20%	9.60%
Other operating expense ratio	[1]	22.50%	21.90%	23.60%	22.70%
Combined ratio		92.90%	93.70%	93.90%	93.50%
International Insurance
Segment Reporting Information [Line Items]
Net earned premiums		$ 68,533	$ 66,278	$ 197,244	$ 187,993
Net losses and LAE		(39,182)	(24,910)	(101,236)	(91,423)
Commission expenses		(12,780)	(12,792)	(35,491)	(32,656)
Other operating expenses		(19,937)	(17,288)	(54,312)	(47,783)
Other underwriting income (expense)			1		18
Underwriting profit (loss)		(3,366)	11,289	6,205	16,149
Income before income taxes		$ (3,366)	$ 11,289	$ 6,205	$ 16,149
Losses and LAE ratio		57.20%	37.60%	51.30%	48.60%
Commission expense ratio		18.60%	19.30%	18.00%	17.40%
Other operating expense ratio	[1]	29.10%	26.10%	27.60%	25.40%
Combined ratio		104.90%	83.00%	96.90%	91.40%
Global Reinsurance
Segment Reporting Information [Line Items]
Net earned premiums		$ 43,140	$ 48,669	$ 124,494	$ 142,866
Net losses and LAE		(22,224)	(29,652)	(70,387)	(92,331)
Commission expenses		(7,705)	(8,831)	(23,042)	(25,171)
Other operating expenses		(3,714)	(3,940)	(11,975)	(11,750)
Other underwriting income (expense)		395	122	441	301
Underwriting profit (loss)		9,892	6,368	19,531	13,915
Income before income taxes		$ 9,892	$ 6,368	$ 19,531	$ 13,915
Losses and LAE ratio		51.50%	60.90%	56.50%	64.60%
Commission expense ratio		17.90%	18.10%	18.50%	17.60%
Other operating expense ratio	[1]	7.70%	7.90%	9.30%	8.10%
Combined ratio		77.10%	86.90%	84.30%	90.30%
Corporate
Segment Reporting Information [Line Items]
Commission expenses	[2]	$ 1,389	$ 550	$ 1,672	$ 1,605
Other underwriting income (expense)	[2]	(1,389)	(550)	(1,672)	(1,605)
Net investment income	[2]	17,371	15,839	50,219	48,097
Net realized gains (losses)	[2]	(757)	6,718	8,755	12,024
Interest expense	[2]	(3,856)	(3,388)	(11,567)	(11,559)
Other income (loss)	[2]	(2,537)	1,229	(4,737)	9,573
Income before income taxes	[2]	10,221	20,398	42,670	58,135
Income tax (expense) benefit	[2]	$ (8,723)	$ (15,032)	$ (30,345)	$ (36,384)

[1] Includes Other operating expenses and Other underwriting income (expense).

[2] Includes Corporate segment intercompany eliminations.