Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities
Net (loss) income	$ (520,291)	$ 852,552	$ 1,536,854
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Amortization of net premium on investments	91,339	78,620	17,312
Amortization of intangible assets	36,405	31,461	(6,133)
Net realized and unrealized investment gains	(66,692)	(401,482)	(591,707)
Net realized gain on purchase of capital efficient notes	0	0	(88,427)
Changes in:
Reinsurance balances, net	(21,036)	217,066	170,986
Reinsurance recoverable on paid and unpaid losses, net of ceded premiums payable	625	(30,033)	(20,836)
Funds held by reinsured companies and funds held - directly managed	606,266	296,174	54,416
Deferred acquisition costs	52,069	35,317	67,899
Net tax assets and liabilities	(58,970)	(56,599)	208,052
Unpaid losses and loss expenses including life policy benefits	606,698	227,240	(112,108)
Unearned premiums	(161,425)	(71,355)	(171,121)
Other, net	8,647	47,959	33,414
Net cash provided by operating activities	573,635	1,226,920	1,098,601
Cash flows from investing activities
Redemptions Of Fixed Maturities	1,211,016	1,272,885	1,065,353
Payments/ proceeds from trading securities [Line Items]
Sales and redemptions of short-term investments	336,456	270,087	201,479
Purchases of short-term investments	(331,432)	(141,157)	(182,211)
Cash acquired related to the acquisition of Paris Re	0	0	492,466	[1]
Other, net	(186,823)	(185,965)	(118,473)
Net cash (used in) provided by investing activities	(1,080,378)	1,102,508	(446,676)
Cash flows from financing activities
Cash dividends paid to shareholders	(205,784)	(192,156)	(151,851)
Net Proceeds From Issuance Of Preferred Stock And Preference Stock	361,722	0	0
Proceeds from issuance of senior notes	0	500,000	0
Repurchase of common shares	(413,737)	(1,065,121)	0
Issuance of common shares	16,041	37,682	16,034
Contract fees on forward sale agreement	0	(2,638)	(5,070)
Repayment of debt	0	(200,000)	(200,000)
Share capital repayment paid to former shareholders of Paris Re	0	0	(330,103)
Purchase of capital efficient notes	0	0	(94,241)
Net cash used in financing activities	(241,758)	(922,233)	(765,231)
Effect of foreign exchange rate changes on cash	(20,326)	(34,420)	13,335
(Decrease) increase in cash and cash equivalents	(768,827)	1,372,775	(99,971)
Cash and cash equivalents - beginning of year	2,111,084	738,309	838,280
Cash and cash equivalents - end of year	1,342,257	2,111,084	738,309
Supplemental cash flow information:
Taxes paid	197,610	199,838	118,174
Interest paid	49,259	42,995	32,476
[FixedMaturitiesMember]
Payments/ proceeds from trading securities [Line Items]
Sales	8,328,352	8,621,227	7,271,909
Purchases	10,549,343	8,572,471	9,039,313
[EquitySecuritiesMember]
Payments/ proceeds from trading securities [Line Items]
Sales	730,929	607,459	688,360
Purchases	$ 619,533	$ 769,557	$ 826,246

[1] The acquisition of Paris Re's assets and liabilities involved non-cash share for share transactions, which have been excluded from the Consolidated Statements of Cash Flows.