Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CASH FROM OPERATING ACTIVITIES:
Net income to common stockholders	$ 510,592	$ 391,211	$ 446,405
Adjustments to reconcile net income to net cash from operating activities:
Net investment (gains) losses	(210,465)	(125,481)	(56,581)
Depreciation and amortization	103,419	88,012	82,867
Noncontrolling interests	51	(70)	279
Investment funds	(77,015)	1,751	49,400
Stock incentive plans	26,763	27,175	27,407
Change in:
Arbitrage trading account	(1,424)	(8,106)	(12,993)
Premiums and fees receivable	(228,756)	(122,468)	(41,167)
Reinsurance accounts	(216,968)	(161,070)	(14,960)
Deferred policy acquisition costs	(38,656)	(38,541)	(10,877)
Deferred income taxes	13,240	43,340	62,353
Reserves for losses and loss expenses	406,763	325,758	(103,745)
Unearned premiums	279,986	238,499	3,414
Other	107,928	10,269	19,514
Net cash from operating activities	675,458	670,279	451,316
CASH FLOWS FROM (USED IN) INVESTING ACTIVITIES:
Proceeds from sale of fixed maturity securities	838,576	1,293,876	1,554,906
Proceeds from sale of equity securities	409,610	159,827	137,990
Distributions from (contributions to) investment funds	77,930	(113,913)	(53,979)
Proceeds from maturities and prepayments of fixed maturity securities	2,291,105	1,697,144	1,374,378
Purchase of fixed maturity securities	(3,617,002)	(2,815,340)	(2,755,449)
Purchase of equity securities	(284,991)	(97,986)	(193,914)
Real Estate purchased	(256,386)	(96,552)	0
Change in loans receivable	(124,776)	92,176	23,317
Net additions to property, furniture and equipment	(40,556)	(45,320)	(49,605)
Change in balances due to (from) security brokers	(25,799)	(16,194)	(297)
Payment for business purchased, net of cash acquired	(42,779)	(261,992)	0
Net cash from (used in) investing activities	(775,068)	(204,274)	37,347
CASH FLOWS FROM (USED IN) FINANCING ACTIVITIES:
Net proceeds from issuance of debt	369,291	0	309,030
Net proceeds from stock options exercised	7,660	21,963	17,730
Repayment of senior notes and other debt	0	(1,310)	(162,685)
Cash dividends to common stockholders	(183,947)	(43,253)	(49,348)
Purchase of common treasury shares	(127,663)	(187,163)	(471,007)
Other	31,851	14,550	(2,795)
Net cash from (used in) financing activities	97,192	(195,213)	(359,075)
Net impact on cash due to change in foreign exchange rates	(3,654)	(2,002)	(2,066)
Net increase (decrease) in cash and cash equivalents	(6,072)	268,790	127,522
Cash and cash equivalents at beginning of year	911,742	642,952	515,430
Cash and cash equivalents at end of year	$ 905,670	$ 911,742	$ 642,952