Reinsurance Balances Recoverable - Additional Information (Detail) (USD $)	3 Months Ended			3 Months Ended		3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2014 Non-Life Run-Off [Member]	Dec. 31, 2013 Non-Life Run-Off [Member]	Mar. 31, 2014 Ceded Credit Risk, Concentrated Credit Risk [Member] One Reinsurer Accounting for More than 10% of Total Reinsurance Balances Receivable [Member]	Dec. 31, 2013 Ceded Credit Risk, Concentrated Credit Risk [Member] One Reinsurer Accounting for More than 10% of Total Reinsurance Balances Receivable [Member]	Mar. 31, 2014 Ceded Credit Risk, Concentrated Credit Risk [Member] Top Ten Reinsurers [Member]	Dec. 31, 2013 Ceded Credit Risk, Concentrated Credit Risk [Member] Top Ten Reinsurers [Member]	Mar. 31, 2014 Ceded Credit Risk, Concentrated Credit Risk [Member] One BBB+ Rated [Member] Standard & Poor's, BBB+ Rating [Member]	Dec. 31, 2012 Ceded Credit Risk, Concentrated Credit Risk [Member] One BBB+ Rated [Member] Standard & Poor's, BBB+ Rating [Member]	Mar. 31, 2014 Ceded Credit Risk, Concentrated Credit Risk [Member] Non-Rated Reinsurer [Member]	Dec. 31, 2012 Ceded Credit Risk, Concentrated Credit Risk [Member] Non-Rated Reinsurer [Member]
Effects of Reinsurance [Line Items]
Reinsurance balances recoverable	$ 1,256,230,000		$ 1,363,819,000	$ 1,196,918,000	$ 1,298,992,000	$ 229,300,000	$ 256,200,000	$ 862,124,000	$ 930,943,000	$ 32,400,000	$ 41,400,000	$ 229,300,000	$ 256,200,000
Reinsurance balance recoverable	(107,994,000)	(49,885,000)		(108,200,000)
Provision for uncollectible reinsurance recoverable relating to total reinsurance recoverable	339,800,000		338,600,000
Ratio of provision for uncollectible reinsurance recoverable to reinsurance balances receivable	21.30%		19.90%
Percentage of top ten reinsurers reinsurance balances recoverable	100.00%		100.00%					68.60%	68.30%
Losses incurred but not reported	$ 359,068,000		$ 413,344,000	$ 346,518,000	$ 402,675,000			$ 253,400,000	$ 290,100,000
Reinsurance recoverable major reinsurer						10.00%