Supplementary Information Concerning P&C Insurance Operations (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Information For Property Casualty Insurance Underwriters [Abstract]
Deferred policy acquisition costs		$ 91,983	$ 79,452	$ 67,007
Reserve for losses and LAE		2,202,644	2,159,634	2,045,071
Unearned premiums		820,676	766,167	714,606
Net earned premiums		984,087	935,895	841,939
Net investment income	[1]	68,571	64,092	56,243
Losses and LAE expenses incurred related to Current year		637,267	601,041	520,227
Losses and LAE expenses incurred related to Prior years		(64,669)	(55,812)	(1,266)
Amortization of deferred policy acquisition costs	[2]	129,977	127,695	115,842
Other operating expenses	[1]	220,643	196,825	164,434
Net written premiums		$ 1,043,860	$ 1,000,138	$ 887,922

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

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