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 PROVIDED BY OPERATING ACTIVITIES:
Net income	$ 274,548	$ 665,005	$ 606,887
Adjustments to reconcile net income to cash provided by operating activities:
Net realized gains on sales of investments	(82,764)	(217,661)	(94,466)
Mark to market adjustments	22,654	(71,909)	(31,886)
Net impairment charges recognized in earnings		168	49,577
Stock compensation expense	22,294	34,243	40,399
Insurance balances receivable	(122,231)	(134,306)	(47,680)
Prepaid reinsurance	(39,434)	(677)	5,972
Reinsurance recoverable	(75,331)	(7,597)	(31,677)
Accrued investment income	2,257	12,526	(2,375)
Net deferred acquisition costs	(3,531)	(8,982)	(1,640)
Net deferred tax assets	129	12,364	(507)
Other assets	22,421	3,390	(26,966)
Reserve for losses and loss expenses	345,955	117,416	184,944
Unearned premiums	116,209	33,584	(1,739)
Reinsurance balances payable	24,807	(3,105)	7,708
Accounts payable and accrued liabilities	10,053	13,969	5,035
Other items, net	30,072	2,836	6,603
Net cash provided by operating activities	548,108	451,264	668,189
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:
Purchases of fixed maturity investments - available for sale	(727)	(133,079)	(6,504,094)
Purchases of fixed maturity investments-trading	(7,472,926)	(12,637,892)	(4,338,454)
Purchases of equity securities	(381,127)	(178,451)	(9,541)
Purchases of other invested assets	(281,957)	(165,505)	(157,307)
Sales of fixed maturity investments-available for sale	609,833	2,687,129	8,346,180
Sales of fixed maturity investments-trading	6,757,787	10,917,962	1,818,736
Sales of equity securities	184,504	18,539	97,505
Sales of other invested assets	71,543	9,746	35,552
Changes in securities lending collateral received			171,026
Purchases of fixed assets	(9,819)	(9,576)	(5,075)
Change in restricted cash	13,765	(8,810)	(37,124)
Net cash (used in) provided by investing activities	(509,124)	500,063	(582,596)
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid		(47,712)	(36,689)
Partial par value reduction	(28,600)
Proceeds from the exercise of stock options	6,837	9,598	7,442
Share repurchase	(86,700)	(674,662)
Proceeds from senior notes		298,632	(243,750)
Debt issuance costs		(1,950)
Purchase of founder warrants	(53,620)	(70,016)
Repayment of syndicated loan			(243,750)
Changes in securities lending collateral		(71,966)	(177,010)
Net cash used in financing activities	(162,083)	(486,110)	(450,007)
Effect of exchange rate changes on foreign currency cash	100	(410)	774
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(122,999)	464,807	(363,640)
CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR	756,995	292,188	655,828
CASH AND CASH EQUIVALENTS, END OF YEAR	633,996	756,995	292,188
Supplemental disclosure of cash flow information:
- Cash paid for income taxes	14,132	22,556	42,170
- Cash paid for interest expense	$ 54,000	$ 37,500	$ 39,115