Losses and Loss Adjustment Expenses - Losses Incurred and Paid Reflected Net of Reinsurance Recoverables (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Effects of Reinsurance [Line Items]
Less: total reinsurance reserves recoverable	$ 1,175,926
Net (reduction) increase in ultimate losses and loss adjustment expense liabilities:
Losses incurred - non-life run-off	(29,182)
Total net (reduction) increase in ultimate losses and loss adjustment expense liabilities	(12,051)	9,161
Net losses paid:
Total net losses paid	(100,522)	(83,674)
Plus: total reinsurance reserves recoverable	1,082,711
Active Underwriting [Member]
Effects of Reinsurance [Line Items]
Balance as at January 1	215,392
Less: total reinsurance reserves recoverable	25,055
Reinsurance reserves recoverable	190,337
Net (reduction) increase in ultimate losses and loss adjustment expense liabilities:
Losses incurred - non-life run-off	21,314
Prior periods	(4,183)
Total net (reduction) increase in ultimate losses and loss adjustment expense liabilities	17,131
Net losses paid:
Current period	(4,684)
Prior periods	(8,151)
Total net losses paid	(12,835)
Effect of exchange rate movement	(7)
Net balance as at March 31	194,626
Plus: total reinsurance reserves recoverable	25,626
Balance as at March 31	220,252
Non-Life Run-Off Segment [Member]
Effects of Reinsurance [Line Items]
Balance as at January 1	4,004,513	3,650,127
Less: total reinsurance reserves recoverable	1,121,533	876,220
Reinsurance reserves recoverable	2,882,980	2,773,907
Net (reduction) increase in ultimate losses and loss adjustment expense liabilities:
Losses incurred - non-life run-off	1,432	28,533
Prior periods	(30,614)	(19,372)
Total net (reduction) increase in ultimate losses and loss adjustment expense liabilities	(29,182)	9,161
Net losses paid:
Current period	(532)	(2,540)
Prior periods	(87,155)	(81,134)
Total net losses paid	(87,687)	(83,674)
Effect of exchange rate movement	(1,025)	(25,952)
Acquired on purchase of subsidiaries		479,982
Assumed business	28,630	42,624
Net balance as at March 31	2,793,716	3,196,048
Plus: total reinsurance reserves recoverable	1,028,162	947,750
Balance as at March 31	$ 3,821,878	$ 4,143,798