Unaudited Condensed Consolidated Statements of Cash Flows (USD $) In Thousands	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Cash flows from operating activities
Net (loss) income	$ (682,771)	$ 270,581
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Amortization of net premium on investments	37,494	37,518
Amortization of intangible assets	17,992	12,636
Net realized and unrealized investment gains (losses)	34,000	(191,519)
Changes in:
Reinsurance balances, net	(361,501)	(443,469)
Reinsurance recoverable on paid and unpaid losses, net of ceded premiums payable	11,481	7,542
Funds held by reinsured companies and funds held - directly managed	552,361	189,635
Deferred acquisition costs	(31,484)	(80,901)
Net tax assets and liabilities	(32,493)	(66,175)
Unpaid losses and loss expenses including life policy benefits	853,057	194,878
Unearned premiums	354,853	638,489
Other net changes in operating assets and liabilities	(10,651)	(8,671)
Net cash provided by operating activities	742,338	560,544
Redemptions of fixed maturities	801,285	561,593
Sales and redemptions of short-term investments	76,061	94,045
Purchases of short-term investments	(240,207)	(69,056)
Other, net	(17,820)	(138,272)
Net cash (used in) provided by investing activities	(1,307,078)	33,090
Cash flows from financing activities
Cash dividends paid to shareholders	(95,009)	(96,608)
Net proceeds from issuance of preferred shares	361,722	0
Repurchase of common shares	(244,222)	(600,086)
Issuance of common shares	13,125	15,013
Proceeds from issuance of senior notes	0	500,000
Contract fees on forward sale agreement	0	(2,638)
Net cash provided by (used in) financing activities	35,616	(184,319)
Effect of foreign exchange rate changes on cash	24,882	(62,299)
(Decrease) increase in cash and cash equivalents	(504,242)	347,016
Cash and cash equivalents - beginning of period	2,111,084	738,309
Cash and cash equivalents - end of period	1,606,842	1,085,325
Supplemental cash flow information:
Taxes paid	103,965	109,841
Interest paid	24,630	17,866
Fixed maturities [Member]
Changes in:
Sales	2,713,137	4,003,008
Purchases	4,766,381	4,248,444
Equity securities [Member]
Changes in:
Sales	457,170	171,643
Purchases	$ 330,323	$ 341,427