Financial Data by Segment (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Net earned premiums		$ 267,992	$ 242,328	$ 532,350	$ 478,460
Net losses and LAE		(167,206)	(141,973)	(320,162)	(272,171)
Commission expenses		(40,726)	(31,480)	(78,280)	(64,385)
Other operating expenses		(59,074)	(52,789)	(119,883)	(107,698)
Other underwriting income (expense)		64	25	73	80
Underwriting profit (loss)		1,050	16,111	14,098	34,286
Net investment income		19,875	16,595	39,469	32,848
Net realized gains (losses)		1,810	3,916	3,407	9,512
Interest expense		(3,858)	(3,856)	(7,716)	(7,711)
Other income (loss)		4,366	(4,387)	6,906	(2,200)
Income before income taxes		23,243	28,379	56,164	66,735
Income tax (expense) benefit		(7,053)	(9,195)	(17,042)	(21,622)
Net income		$ 16,190	$ 19,184	$ 39,122	$ 45,113
Losses and LAE ratio		62.40%	58.60%	60.10%	56.90%
Commission expense ratio		15.20%	13.00%	14.70%	13.50%
Other operating expense ratio	[1]	22.00%	21.80%	22.60%	22.40%
Combined ratio		99.60%	93.40%	97.40%	92.80%
U.S.Insurance
Segment Reporting Information [Line Items]
Net earned premiums		$ 152,384	$ 137,304	$ 300,724	$ 268,395
Net losses and LAE		(93,428)	(84,155)	(184,940)	(161,954)
Commission expenses		(16,894)	(12,275)	(31,749)	(26,620)
Other operating expenses		(31,570)	(31,374)	(65,331)	(65,062)
Other underwriting income (expense)		342	121	703	317
Underwriting profit (loss)		10,834	9,621	19,407	15,076
Income before income taxes		$ 10,834	$ 9,621	$ 19,407	$ 15,076
Losses and LAE ratio		61.30%	61.30%	61.50%	60.30%
Commission expense ratio		11.10%	8.90%	10.60%	9.90%
Other operating expense ratio	[1]	20.50%	22.80%	21.40%	24.20%
Combined ratio		92.90%	93.00%	93.50%	94.40%
International Insurance
Segment Reporting Information [Line Items]
Net earned premiums		$ 77,833	$ 63,186	$ 155,841	$ 128,711
Net losses and LAE		(48,066)	(32,363)	(88,476)	(62,054)
Commission expenses		(16,821)	(11,298)	(32,176)	(22,711)
Other operating expenses		(23,043)	(17,366)	(44,814)	(34,375)
Underwriting profit (loss)		(10,097)	2,159	(9,625)	9,571
Income before income taxes		$ (10,097)	$ 2,159	$ (9,625)	$ 9,571
Losses and LAE ratio		61.80%	51.20%	56.80%	48.20%
Commission expense ratio		21.60%	17.90%	20.60%	17.60%
Other operating expense ratio	[1]	29.60%	27.50%	28.80%	26.80%
Combined ratio		113.00%	96.60%	106.20%	92.60%
Global Reinsurance
Segment Reporting Information [Line Items]
Net earned premiums		$ 37,775	$ 41,838	$ 75,785	$ 81,354
Net losses and LAE		(25,712)	(25,455)	(46,746)	(48,163)
Commission expenses		(7,492)	(8,039)	(15,237)	(15,337)
Other operating expenses		(4,461)	(4,049)	(9,738)	(8,261)
Other underwriting income (expense)		203	36	252	46
Underwriting profit (loss)		313	4,331	4,316	9,639
Income before income taxes		$ 313	$ 4,331	$ 4,316	$ 9,639
Losses and LAE ratio		68.10%	60.80%	61.70%	59.20%
Commission expense ratio		19.80%	19.20%	20.10%	18.90%
Other operating expense ratio	[1]	11.30%	9.60%	12.50%	10.10%
Combined ratio		99.20%	89.60%	94.30%	88.20%
Corporate
Segment Reporting Information [Line Items]
Commission expenses	[2]	$ 481	$ 132	$ 882	$ 283
Other underwriting income (expense)	[2]	(481)	(132)	(882)	(283)
Net investment income	[2]	19,875	16,595	39,469	32,848
Net realized gains (losses)	[2]	1,810	3,916	3,407	9,512
Interest expense	[2]	(3,858)	(3,856)	(7,716)	(7,711)
Other income (loss)	[2]	4,366	(4,387)	6,906	(2,200)
Income before income taxes	[2]	22,193	12,268	42,066	32,449
Income tax (expense) benefit	[2]	$ (7,053)	$ (9,195)	$ (17,042)	$ (21,622)

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

[2] Includes Corporate segment intercompany eliminations.