Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
CASH FLOWS PROVIDED BY OPERATING ACTIVITIES:
Net income	$ 490,259	$ 417,880	$ 493,007
Adjustments to reconcile net income to cash provided by operating activities:
Net realized (gains) losses on sales of investments	(144,972)	(109,084)	55,865
Mark to market adjustments	21,984	48,147	(180,380)
Stock compensation expense	14,245	13,969	17,642
Undistributed income of equity method investments	13,851	(11,923)	0
Changes in:
Reserve for losses and loss expenses, net of reinsurance recoverables	8,884	27,586	282,215
Unearned premiums, net of prepaid reinsurance	139,317	114,649	88,924
Insurance balances receivable	(76,825)	(108,412)	(81,600)
Reinsurance recoverable on paid losses	(8,509)	(45,787)	(1,594)
Funds held	(91,591)	(296,062)	(111,548)
Reinsurance balances payable	7,037	36,759	11,725
Net deferred acquisition costs	(24,885)	(18,651)	(7,676)
Net deferred tax assets	4,186	(11,889)	200
Accounts payable and accrued liabilities	8,039	22,917	27,815
Other items, net	55,829	34,332	34,843
Net cash provided by operating activities	416,849	114,431	629,438
CASH FLOWS USED IN INVESTING ACTIVITIES:
Purchases of trading securities	(7,630,034)	(7,527,670)	(8,006,237)
Purchases of other invested assets	(307,955)	(276,926)	(333,031)
Sales of available for sale securities	0	0	236,978
Sales of trading securities	7,536,936	7,540,194	7,892,907
Sales of other invested assets	267,885	187,477	53,741
Purchases of fixed assets	(59,656)	(5,310)	(3,214)
Net cash paid for acquisitions	(2,565)	0	0
Change in restricted cash	68,422	34,092	(100,877)
Net cash used in investing activities	(126,967)	(48,143)	(259,733)
CASH FLOWS USED IN FINANCING ACTIVITIES:
Dividends paid — par value reduction	0	(12,981)	(67,825)
Dividends paid	(76,750)	(34,059)	0
Proceeds from the exercise of stock options	10,027	12,137	10,527
Proceeds from other long-term debt	19,213	0	0
Share repurchases	(175,910)	(173,006)	(263,942)
Net cash used in financing activities	(223,420)	(207,909)	(321,240)
Effect of exchange rate changes on foreign currency cash	(9,059)	(8,322)	(582)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	57,403	(149,943)	47,883
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	531,936	681,879	633,996
CASH AND CASH EQUIVALENTS, END OF PERIOD	589,339	531,936	681,879
Supplemental disclosure of cash flow information:
Cash paid for income taxes	18,363	22,604	23,957
Cash paid for interest expense	$ 54,000	$ 54,000	$ 54,000