Financial Data by Segment (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Net earned premiums		$ 284,010	$ 254,082	$ 816,360	$ 732,542
Net losses and LAE		(172,793)	(146,546)	(492,955)	(418,717)
Commission expenses		(42,611)	(34,253)	(120,891)	(98,638)
Other operating expenses		(56,137)	(56,599)	(176,020)	(164,297)
Other underwriting income (expense)		44	19	117	99
Underwriting profit (loss)		12,513	16,703	26,611	50,989
Net investment income		19,875	17,371	59,344	50,219
Net realized gains (losses)		1,586	(757)	4,993	8,755
Interest expense		(3,859)	(3,856)	(11,575)	(11,567)
Other income (loss)		(227)	(2,537)	6,679	(4,737)
Income before income taxes		29,888	26,924	86,052	93,659
Income tax (expense) benefit		(7,875)	(8,723)	(24,917)	(30,345)
Net income		$ 22,013	$ 18,201	$ 61,135	$ 63,314
Losses and LAE ratio		60.80%	57.70%	60.40%	57.20%
Commission expense ratio		15.00%	13.50%	14.80%	13.50%
Other operating expense ratio	[1]	19.80%	22.20%	21.50%	22.30%
Combined ratio		95.60%	93.40%	96.70%	93.00%
U.S.Insurance
Segment Reporting Information [Line Items]
Net earned premiums		$ 161,722	$ 142,409	$ 462,446	$ 410,804
Net losses and LAE		(106,320)	(85,140)	(291,260)	(247,094)
Commission expenses		(18,630)	(15,157)	(50,379)	(41,777)
Other operating expenses		(31,517)	(32,948)	(96,848)	(98,010)
Other underwriting income (expense)		240	1,013	943	1,330
Underwriting profit (loss)		5,495	10,177	24,902	25,253
Income before income taxes		$ 5,495	$ 10,177	$ 24,902	$ 25,253
Losses and LAE ratio		65.70%	59.80%	63.00%	60.10%
Commission expense ratio		11.50%	10.60%	10.90%	10.20%
Other operating expense ratio	[1]	19.40%	22.50%	20.70%	23.60%
Combined ratio		96.60%	92.90%	94.60%	93.90%
International Insurance
Segment Reporting Information [Line Items]
Net earned premiums		$ 79,761	$ 68,533	$ 235,602	$ 197,244
Net losses and LAE		(45,043)	(39,182)	(133,519)	(101,236)
Commission expenses		(15,348)	(12,780)	(47,524)	(35,491)
Other operating expenses		(20,183)	(19,937)	(64,997)	(54,312)
Underwriting profit (loss)		(813)	(3,366)	(10,438)	6,205
Income before income taxes		$ (813)	$ (3,366)	$ (10,438)	$ 6,205
Losses and LAE ratio		56.50%	57.20%	56.70%	51.30%
Commission expense ratio		19.20%	18.60%	20.20%	18.00%
Other operating expense ratio	[1]	25.30%	29.10%	27.50%	27.60%
Combined ratio		101.00%	104.90%	104.40%	96.90%
Global Reinsurance
Segment Reporting Information [Line Items]
Net earned premiums		$ 42,527	$ 43,140	$ 118,312	$ 124,494
Net losses and LAE		(21,430)	(22,224)	(68,176)	(70,387)
Commission expenses		(8,951)	(7,705)	(24,188)	(23,042)
Other operating expenses		(4,437)	(3,714)	(14,175)	(11,975)
Other underwriting income (expense)		122	395	374	441
Underwriting profit (loss)		7,831	9,892	12,147	19,531
Income before income taxes		$ 7,831	$ 9,892	$ 12,147	$ 19,531
Losses and LAE ratio		50.40%	51.50%	57.60%	56.50%
Commission expense ratio		21.00%	17.90%	20.40%	18.50%
Other operating expense ratio	[1]	10.20%	7.70%	11.70%	9.30%
Combined ratio		81.60%	77.10%	89.70%	84.30%
Corporate
Segment Reporting Information [Line Items]
Commission expenses	[2]	$ 318	$ 1,389	$ 1,200	$ 1,672
Other underwriting income (expense)	[2]	(318)	(1,389)	(1,200)	(1,672)
Net investment income	[2]	19,875	17,371	59,344	50,219
Net realized gains (losses)	[2]	1,586	(757)	4,993	8,755
Interest expense	[2]	(3,859)	(3,856)	(11,575)	(11,567)
Other income (loss)	[2]	(227)	(2,537)	6,679	(4,737)
Income before income taxes	[2]	17,375	10,221	59,441	42,670
Income tax (expense) benefit	[2]	$ (7,875)	$ (8,723)	$ (24,917)	$ (30,345)

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

[2] Includes Corporate segment intercompany eliminations.