Liability for Unpaid Loss and Loss Adjustment Expense (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract
Reserves at beginning of year	$ 3,902,132	$ 3,767,850
Less reinsurance recoverables on reserves	1,122,731	1,018,047
Net reserves at beginning of period	2,779,401	2,749,803
Foreign currency adjustment	2,552	(21,729)
Net loss and loss adjustment expense:
Net loss and loss adjustment expense	321,844	332,697
Net loss and loss adjustment expense payments for claims occurring during:
Net loss and loss adjustment expense payments	(354,956)	(299,529)
Net reserves at end of period	2,748,841	2,761,242
Plus reinsurance recoverables on reserves	1,098,576	1,012,920
Reserves at end of period	$ 3,847,417	$ 3,774,162