Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities
Net income	$ 787,996	$ 397,517
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of net premium on investments	82,519	119,468
Amortization of intangible assets	21,007	21,136
Net realized and unrealized investment (gains) losses	(273,468)	260,154
Changes in:
Reinsurance balances, net	(565,187)	(592,380)
Reinsurance recoverable on paid and unpaid losses, net of ceded premiums payable	32,421	65,593
Funds held by reinsured companies and funds held – directly managed	138,659	76,159
Deferred acquisition costs	(83,758)	(111,562)
Net tax assets and liabilities	(27,792)	(83,379)
Unpaid losses and loss expenses including life policy benefits	144,663	(65,725)
Unearned premiums	336,384	433,740
Other net changes in operating assets and liabilities	(10,207)	63,014
Net cash provided by operating activities	583,237	583,735
Payments/ proceeds from trading securities [Line Items]
Redemptions of fixed maturities	527,367	1,002,991
Sales and redemptions of short-term investments	70,750	290,011
Purchases of short-term investments	(95,168)	(176,339)
Other, net	(4,822)	98,813
Net cash (used in) provided by investing activities	(2,579)	584,512
Cash flows from financing activities
Dividends paid to common and preferred shareholders	(144,004)	(151,869)
Repurchase of common shares	(374,557)	(619,534)
Issuance of common shares, net of taxes paid	12,639	37,193
Net proceeds from issuance of preferred shares	0	241,265
Repurchase of preferred shares	0	(290,000)
(Distribution) sale of shares to noncontrolling interests	(14,265)	47,136
Net cash used in financing activities	(520,187)	(735,809)
Effect of foreign exchange rate changes on cash	(37,669)	(3,081)
Increase in cash and cash equivalents	22,802	429,357
Cash and cash equivalents—beginning of period	1,496,485	1,121,705
Cash and cash equivalents—end of period	1,519,287	1,551,062
Supplemental cash flow information:
Taxes paid	243,396	148,522
Interest paid	24,630	24,630
Fixed maturities [Member]
Payments/ proceeds from trading securities [Line Items]
Sales of fixed maturities and sales of equities	6,227,896	5,831,364
Purchases of fixed maturities and purchases of equities	(6,990,492)	(6,501,873)
Equities [Member]
Payments/ proceeds from trading securities [Line Items]
Sales of fixed maturities and sales of equities	464,212	595,848
Purchases of fixed maturities and purchases of equities	$ (202,322)	$ (556,303)