Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CASH FLOWS PROVIDED BY OPERATING ACTIVITIES:
Net income	$ 493,007	$ 274,548	$ 665,005
Adjustments to reconcile net income to cash provided by operating activities:
Net realized gains (losses) on sales of investments	55,865	(82,764)	(217,661)
Mark to market adjustments	(180,380)	22,654	(71,909)
Stock compensation expense	17,642	22,294	34,243
Net impairment charges recognized in earnings	0	0	168
Changes in:
Reserve for losses and loss expenses, net of reinsurance recoverables	282,215	270,624	109,819
Unearned premiums, net of prepaid reinsurance	88,924	76,775	32,907
Insurance balances receivable	(194,742)	(122,231)	(134,306)
Reinsurance balances payable	11,725	24,807	(3,105)
Net deferred acquisition costs	(7,676)	(3,531)	(8,982)
Net deferred tax assets	200	129	12,364
Accounts payable and accrued liabilities	27,815	10,053	13,969
Other items, net	34,843	54,750	18,752
Net cash provided by operating activities	629,438	548,108	451,264
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:
Purchases of available for sale securities	0	(727)	(133,079)
Purchases of trading securities	(8,006,237)	(7,854,053)	(12,816,343)
Purchases of other invested assets	(333,031)	(281,957)	(165,505)
Sales of available for sale securities	236,978	609,833	2,687,129
Sales of trading securities	7,892,907	6,942,291	10,936,501
Sales of other invested assets	53,741	71,543	9,746
Purchases of fixed assets	(3,214)	(9,819)	(9,576)
Change in restricted cash	(100,877)	13,765	(8,810)
Net cash (used in) provided by investing activities	(259,733)	(509,124)	500,063
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid - par value reduction	(67,825)	(28,600)	0
Dividends paid	0	0	(47,712)
Proceeds from the exercise of stock options	10,527	6,837	9,598
Share repurchases	(263,942)	(86,700)	(674,662)
Repurchase of founder warrants	0	(53,620)	(70,016)
Proceeds from senior notes	0	0	296,682
Net cash used in financing activities	(321,240)	(162,083)	(486,110)
Effect of exchange rate changes on foreign currency cash	(582)	100	(410)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	47,883	(122,999)	464,807
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	633,996	756,995	292,188
CASH AND CASH EQUIVALENTS, END OF PERIOD	681,879	633,996	756,995
Supplemental disclosure of cash flow information:
- Cash paid for income taxes	23,957	14,132	22,556
- Cash paid for interest expense	$ 54,000	$ 54,000	$ 37,500