Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
CASH FLOWS PROVIDED BY OPERATING ACTIVITIES:
Net income	$ 417,880	$ 493,007	$ 274,548
Adjustments to reconcile net income to cash provided by operating activities:
Net realized (gains) losses on sales of investments	(109,084)	55,865	(82,764)
Mark to market adjustments	48,147	(180,380)	22,654
Stock compensation expense	13,969	17,642	22,294
Undistributed income of equity method investments	(11,923)	0	0
Changes in:
Reserve for losses and loss expenses, net of reinsurance recoverables	27,586	282,215	270,624
Unearned premiums, net of prepaid reinsurance	114,649	88,924	76,775
Insurance balances receivable	(154,199)	(83,194)	(66,401)
Funds held	(296,062)	(111,548)	(55,830)
Reinsurance balances payable	36,759	11,725	24,807
Net deferred acquisition costs	(18,651)	(7,676)	(3,531)
Net deferred tax assets	(11,889)	200	129
Accounts payable and accrued liabilities	22,917	27,815	10,053
Other items, net	34,332	34,843	54,750
Net cash provided by operating activities	114,431	629,438	548,108
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of available for sale securities	0	0	(727)
Purchases of trading securities	(7,527,670)	(8,006,237)	(7,854,053)
Purchases of other invested assets	(276,926)	(333,031)	(281,957)
Sales of available for sale securities	0	236,978	609,833
Sales of trading securities	7,540,194	7,892,907	6,942,291
Sales of other invested assets	187,477	53,741	71,543
Purchases of fixed assets	(5,310)	(3,214)	(9,819)
Change in restricted cash	34,092	(100,877)	13,765
Net cash used in investing activities	(48,143)	(259,733)	(509,124)
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid — par value reduction	(12,981)	(67,825)	(28,600)
Dividends paid	(34,059)	0	0
Proceeds from the exercise of stock options	12,137	10,527	6,837
Share repurchases	(173,006)	(263,942)	(86,700)
Repurchase of founder warrants	0	0	(53,620)
Net cash used in financing activities	(207,909)	(321,240)	(162,083)
Effect of Exchange Rate on Cash and Cash Equivalents, Continuing Operations	(8,322)	(582)	100
NET(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(149,943)	47,883	(122,999)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	681,879	633,996	756,995
CASH AND CASH EQUIVALENTS, END OF PERIOD	531,936	681,879	633,996
Supplemental disclosure of cash flow information:
Cash paid for income taxes	22,604	23,957	14,132
Cash paid for interest expense	$ 54,000	$ 54,000	$ 54,000