Unaudited Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities
Net income (loss)	$ 1,022,994	$ (502,648)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Amortization of net premium on investments	99,722	63,268
Amortization of intangible assets	26,679	27,512
Net realized and unrealized investment (gains) losses	(488,296)	7,860
Changes in:
Reinsurance balances, net	(202,270)	(228,133)
Reinsurance recoverable on paid and unpaid losses, net of ceded premiums payable	59,536	(1,923)
Funds held by reinsured companies and funds held - directly managed	110,096	573,220
Deferred acquisition costs	(51,722)	8,716
Net tax assets and liabilities	89,900	(2,893)
Unpaid losses and loss expenses including life policy benefits	(557,411)	500,038
Unearned premiums	334,772	140,091
Other net changes in operating assets and liabilities	25,355	(1,176)
Net cash provided by operating activities	469,355	583,932
Cash flows from investing activities
Redemptions Of Fixed Maturities	705,423	967,020
Payments/ proceeds from trading securities [Line Items]
Sales and redemptions of short-term investments	61,903	242,234
Purchases of short-term investments	(176,068)	(292,833)
Other, net	33,891	(131,989)
Net cash used in investing activities	(11,210)	(1,599,055)
Cash flows from financing activities
Cash dividends paid to shareholders	(164,368)	(150,006)
Net proceeds from issuance of preferred shares	0	361,722
Repurchase of common shares	(312,291)	(244,222)
Issuance of common shares	19,117	13,219
Net cash used in financing activities	(457,542)	(19,287)
Effect of foreign exchange rate changes on cash	(6,498)	(3,242)
Decrease in cash and cash equivalents	(5,895)	(1,037,652)
Cash and cash equivalents - beginning of period	1,342,257	2,111,084
Cash and cash equivalents - end of period	1,336,362	1,073,432
Supplemental cash flow information:
Taxes paid	105,059	136,188
Interest paid	24,630	24,630
[FixedMaturitiesMember]
Payments/ proceeds from trading securities [Line Items]
Sales	5,016,192	5,049,822
Purchases	(5,649,511)	(7,412,275)
[EquitySecuritiesMember]
Payments/ proceeds from trading securities [Line Items]
Sales	574,612	492,491
Purchases	$ (577,652)	$ (513,525)