Supplementary Insurance Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	$ 67,007		$ 61,005		$ 63,984
Reserve for losses and loss adjustment expenses	2,045,071		2,097,048		2,082,679
Unearned premiums	714,606		642,407		532,628
Other policy claims and benefits payable
Net earned premiums	841,939		781,964		691,645
Net investment income	56,243	[1]	54,100	[1]	63,119	[1]
Losses and loss adjustment expenses incurred	518,961		497,433		476,997
Amortization of deferred policy acquisition costs	115,842	[2]	123,819	[2]	112,506	[2]
Other operating expenses	164,434	[1]	159,079	[1]	138,029	[1]
Net written premiums	887,922		833,655		753,798
Insurance
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	54,984		48,294		47,298
Reserve for losses and loss adjustment expenses	1,523,175		1,567,045		1,517,331
Unearned premiums	536,303		470,425		384,596
Other policy claims and benefits payable
Net earned premiums	639,338		571,439		472,463
Net investment income	49,083	[1]	46,549	[1]	54,164	[1]
Losses and loss adjustment expenses incurred	415,413		417,082		341,625
Amortization of deferred policy acquisition costs	81,132	[2]	81,370	[2]	64,165	[2]
Other operating expenses	119,920	[1]	113,625	[1]	101,517	[1]
Net written premiums	680,008		622,956		542,391
Lloyd's
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	12,023		12,711		16,686
Reserve for losses and loss adjustment expenses	521,896		530,003		565,348
Unearned premiums	178,303		171,982		148,032
Other policy claims and benefits payable
Net earned premiums	202,601		210,525		219,182
Net investment income	7,160	[1]	7,551	[1]	8,955	[1]
Losses and loss adjustment expenses incurred	103,548		80,351		135,372
Amortization of deferred policy acquisition costs	34,710	[2]	42,449	[2]	48,341	[2]
Other operating expenses	44,514	[1]	45,454	[1]	36,512	[1]
Net written premiums	$ 207,914		$ 210,699		$ 211,407

[1] Net investment income and Other operating expenses reflect only such amounts attributable to the Company's insurance operations.

[2] Amortization of deferred policy acquisition costs reflects only such amounts attributable to the Company's insurance operations. A portion of these costs is eliminated in consolidation.