Financial Data by Segment (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Net earned premiums		$ 242,328	$ 231,084	$ 478,460	$ 456,356
Net losses and LAE		(141,973)	(140,220)	(272,171)	(275,287)
Commission expenses		(31,480)	(32,150)	(64,385)	(57,877)
Other operating expenses		(52,789)	(47,992)	(107,698)	(95,138)
Other underwriting income (expense)		25	235	80	390
Underwriting profit (loss)		16,111	10,957	34,286	28,444
Net investment income		16,595	15,648	32,848	32,258
Net realized gains (losses)		3,916	4,473	9,512	5,306
Interest expense		(3,856)	(4,319)	(7,711)	(8,171)
Other income (loss)		(4,387)	(1,900)	(2,200)	8,344
Income (loss) before income taxes		28,379	24,859	66,735	66,181
Income tax (expense) benefit		(9,195)	(7,998)	(21,622)	(21,352)
Net income (loss)		$ 19,184	$ 16,861	$ 45,113	$ 44,829
Losses and LAE ratio		58.60%	60.70%	56.90%	60.30%
Commission expense ratio		13.00%	13.90%	13.50%	12.70%
Other operating expense ratio	[1]	21.80%	20.70%	22.40%	20.80%
Combined ratio		93.40%	95.30%	92.80%	93.80%
U.S.Insurance
Segment Reporting Information [Line Items]
Net earned premiums		$ 137,304	$ 125,254	$ 268,395	$ 240,444
Net losses and LAE		(84,155)	(73,131)	(161,954)	(146,095)
Commission expenses		(12,275)	(13,219)	(26,620)	(22,728)
Other operating expenses		(31,374)	(28,840)	(65,062)	(56,833)
Other underwriting income (expense)		121	736	317	1,249
Underwriting profit (loss)		9,621	10,800	15,076	16,037
Income (loss) before income taxes		$ 9,621	$ 10,800	$ 15,076	$ 16,037
Losses and LAE ratio		61.30%	58.40%	60.30%	60.80%
Commission expense ratio		8.90%	10.60%	9.90%	9.50%
Other operating expense ratio	[1]	22.80%	22.40%	24.20%	23.00%
Combined ratio		93.00%	91.40%	94.40%	93.30%
International Insurance
Segment Reporting Information [Line Items]
Net earned premiums		$ 63,186	$ 59,661	$ 128,711	$ 121,715
Net losses and LAE		(32,363)	(35,293)	(62,054)	(66,513)
Commission expenses		(11,298)	(11,009)	(22,711)	(19,864)
Other operating expenses		(17,366)	(15,436)	(34,375)	(30,495)
Other underwriting income (expense)			11		17
Underwriting profit (loss)		2,159	(2,066)	9,571	4,860
Income (loss) before income taxes		$ 2,159	$ (2,066)	$ 9,571	$ 4,860
Losses and LAE ratio		51.20%	59.20%	48.20%	54.60%
Commission expense ratio		17.90%	18.50%	17.60%	16.30%
Other operating expense ratio	[1]	27.50%	25.80%	26.80%	25.10%
Combined ratio		96.60%	103.50%	92.60%	96.00%
Global Reinsurance
Segment Reporting Information [Line Items]
Net earned premiums		$ 41,838	$ 46,169	$ 81,354	$ 94,197
Net losses and LAE		(25,455)	(31,796)	(48,163)	(62,679)
Commission expenses		(8,039)	(8,468)	(15,337)	(16,340)
Other operating expenses		(4,049)	(3,716)	(8,261)	(7,810)
Other underwriting income (expense)		36	34	46	179
Underwriting profit (loss)		4,331	2,223	9,639	7,547
Income (loss) before income taxes		$ 4,331	$ 2,223	$ 9,639	$ 7,547
Losses and LAE ratio		60.80%	68.90%	59.20%	66.50%
Commission expense ratio		19.20%	18.30%	18.90%	17.30%
Other operating expense ratio	[1]	9.60%	8.00%	10.10%	8.20%
Combined ratio		89.60%	95.20%	88.20%	92.00%
Corporate
Segment Reporting Information [Line Items]
Commission expenses	[2]	$ 132	$ 546	$ 283	$ 1,055
Other underwriting income (expense)	[2]	(132)	(546)	(283)	(1,055)
Net investment income	[2]	16,595	15,648	32,848	32,258
Net realized gains (losses)	[2]	3,916	4,473	9,512	5,306
Interest expense	[2]	(3,856)	(4,319)	(7,711)	(8,171)
Other income (loss)	[2]	(4,387)	(1,900)	(2,200)	8,344
Income (loss) before income taxes	[2]	12,268	13,902	32,449	37,737
Income tax (expense) benefit	[2]	$ (9,195)	$ (7,998)	$ (21,622)	$ (21,352)

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

[2] Includes Corporate segment intercompany eliminations.