Financial Data by Segment (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Net Earned Premiums		$ 293,835	$ 267,992	$ 579,966	$ 532,350
Net Losses and LAE		(177,110)	(167,206)	(346,710)	(320,162)
Commission Expenses		(48,173)	(40,726)	(96,017)	(78,280)
Other Operating Expenses		(60,766)	(59,074)	(119,304)	(119,883)
Other Underwriting Income (Expense)		11	64	32	73
Underwriting Profit (Loss)		7,797	1,050	17,967	14,098
Net Investment Income		22,265	19,875	43,713	39,469
Net Realized Gains		1,694	1,810	1,650	3,407
Interest Expense		(3,861)	(3,858)	(7,722)	(7,716)
Other Income (Loss)		(422)	4,366	625	6,906
Income Before Income Taxes		27,473	23,243	56,233	56,164
Income Tax Expense		(6,971)	(7,053)	(14,621)	(17,042)
Net Income		$ 20,502	$ 16,190	$ 41,612	$ 39,122
Losses and LAE Ratio		60.30%	62.40%	59.80%	60.10%
Commission Expense Ratio		16.40%	15.20%	16.60%	14.70%
Other Operating Expense Ratio	[1]	20.60%	22.00%	20.50%	22.60%
Combined Ratio		97.30%	99.60%	96.90%	97.40%
U.S.Insurance
Segment Reporting Information [Line Items]
Net Earned Premiums		$ 167,087	$ 152,384	$ 331,091	$ 300,724
Net Losses and LAE		(105,270)	(93,428)	(204,096)	(184,940)
Commission Expenses		(20,460)	(16,894)	(40,844)	(31,749)
Other Operating Expenses		(33,140)	(31,570)	(66,612)	(65,331)
Other Underwriting Income (Expense)		100	342	210	703
Underwriting Profit (Loss)		8,317	10,834	19,749	19,407
Income Before Income Taxes		$ 8,317	$ 10,834	$ 19,749	$ 19,407
Losses and LAE Ratio		63.00%	61.30%	61.60%	61.50%
Commission Expense Ratio		12.20%	11.10%	12.30%	10.60%
Other Operating Expense Ratio	[1]	19.80%	20.50%	20.10%	21.40%
Combined Ratio		95.00%	92.90%	94.00%	93.50%
International Insurance
Segment Reporting Information [Line Items]
Net Earned Premiums		$ 82,100	$ 77,833	$ 166,186	$ 155,841
Net Losses and LAE		(44,095)	(48,066)	(94,800)	(88,476)
Commission Expenses		(19,001)	(16,821)	(38,234)	(32,176)
Other Operating Expenses		(22,506)	(23,043)	(42,299)	(44,814)
Underwriting Profit (Loss)		(3,502)	(10,097)	(9,147)	(9,625)
Income Before Income Taxes		$ (3,502)	$ (10,097)	$ (9,147)	$ (9,625)
Losses and LAE Ratio		53.70%	61.80%	57.00%	56.80%
Commission Expense Ratio		23.10%	21.60%	23.00%	20.60%
Other Operating Expense Ratio	[1]	27.50%	29.60%	25.50%	28.80%
Combined Ratio		104.30%	113.00%	105.50%	106.20%
Global Reinsurance
Segment Reporting Information [Line Items]
Net Earned Premiums		$ 44,648	$ 37,775	$ 82,689	$ 75,785
Net Losses and LAE		(27,745)	(25,712)	(47,814)	(46,746)
Commission Expenses		(8,970)	(7,492)	(17,462)	(15,237)
Other Operating Expenses		(5,120)	(4,461)	(10,393)	(9,738)
Other Underwriting Income (Expense)		169	203	345	252
Underwriting Profit (Loss)		2,982	313	7,365	4,316
Income Before Income Taxes		$ 2,982	$ 313	$ 7,365	$ 4,316
Losses and LAE Ratio		62.10%	68.10%	57.80%	61.70%
Commission Expense Ratio		20.10%	19.80%	21.10%	20.10%
Other Operating Expense Ratio	[1]	11.10%	11.30%	12.20%	12.50%
Combined Ratio		93.30%	99.20%	91.10%	94.30%
Corporate
Segment Reporting Information [Line Items]
Net Investment Income	[2]	$ 22,265	$ 19,875	$ 43,713	$ 39,469
Net Realized Gains	[2]	1,694	1,810	1,650	3,407
Interest Expense	[2]	(3,861)	(3,858)	(7,722)	(7,716)
Other Income (Loss)	[2]	(422)	4,366	625	6,906
Income Before Income Taxes	[2]	19,676	22,193	38,266	42,066
Income Tax Expense	[2]	(6,971)	(7,053)	(14,621)	(17,042)
Intersegment Elimination
Segment Reporting Information [Line Items]
Commission Expenses	[2]	258	481	523	882
Other Underwriting Income (Expense)	[2]	$ (258)	$ (481)	$ (523)	$ (882)

[1] Includes Other Operating Expenses and Other Underwriting Income (Expense).

[2] Includes Corporate segment intercompany eliminations.