Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 85,262	$ 125,653	$ 370,913	$ 340,377
Adjustments to reconcile net income to net cash provided by operating activities:
Decrease (increase) in premiums receivable	(145,988)	66,341	(197,543)	103,547
Decrease (increase) in funds held by reinsureds, net	(6,364)	22,830	(12,486)	(17,524)
Decrease (increase) in reinsurance receivables	(64,010)	22,823	(86,152)	30,491
Decrease (increase) in current income taxes	(17,133)	5,526	12,779	4,628
Decrease (increase) in deferred tax asset	8,436	38,950	110,623	113,624
Decrease (increase) in prepaid reinsurance premiums	(37,771)	90,785	(54,149)	95,321
Increase (decrease) in reserve for losses and loss adjustment expenses	(77,864)	(131,146)	(254,292)	(297,135)
Increase (decrease) in unearned premiums	78,867	(190,678)	122,814	(201,002)
Increase (decrease) in other net payable to reinsurers	121,516	38,445	116,897	42,550
Increase (decrease) in losses in course of payment	73,102	(27,312)	235,534	10,589
Change in equity adjustments in limited partnerships	(13,602)	(8,765)	(24,822)	(20,050)
Change in other assets and liabilities, net	(24,739)	82,274	(11,751)	88,755
Non-cash compensation expense	1,800	1,628	3,973	3,244
Amortization of bond premium (accrual of bond discount)	7,134	5,335	13,697	9,609
Amortization of underwriting discount on senior notes	14	12	27	25
Net realized capital (gains) losses	(15,526)	(82,589)	(325,332)	(258,730)
Net cash provided by (used in) operating activities	(26,866)	60,112	20,730	48,319
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from fixed maturities matured/called - available for sale, at market value	329,143	172,534	627,384	374,721
Proceeds from fixed maturities matured/called - available for sale, at fair value	4,213		7,213
Proceeds from fixed maturities sold - available for sale, at market value	173,690	92,165	340,624	176,301
Proceeds from fixed maturities sold - available for sale, at fair value	13,678	1,862	17,342	61,143
Proceeds from equity securities sold - available for sale, at fair value	251,018	52,340	354,846	291,880
Distributions from other invested assets	27,311	9,522	59,788	15,383
Cost of fixed maturities acquired - available for sale, at market value	(414,379)	(369,223)	(1,000,902)	(662,071)
Cost of fixed maturities acquired - available for sale, at fair value	(1,411)	(2,382)	(2,706)	(5,506)
Cost of equity securities acquired - available for sale, at fair value	(113,147)	(75,674)	(233,674)	(180,888)
Cost of other invested assets acquired	(3,847)	(12,130)	(8,508)	(23,766)
Net change in short-term investments	13,055	64,548	96,677	(157,589)
Net change in unsettled securities transactions	(14,825)	(24,657)	(32,383)	5,112
Net cash provided by (used in) investing activities	264,499	(91,095)	225,701	(105,280)
CASH FLOWS FROM FINANCING ACTIVITIES:
Tax benefit from share-based compensation	1,098	143	2,083	153
Revolving credit borrowings	40,000		40,000
Net cost of junior subordinated debt securities maturing	(329,897)		(329,897)
Net cash provided by (used in) financing activities	(288,799)	143	(287,814)	153
EFFECT OF EXCHANGE RATE CHANGES ON CASH	(1,157)	(8,174)	(14,705)	14,274
Net increase (decrease) in cash	(52,323)	(39,014)	(56,088)	(42,534)
Cash, beginning of period	343,955	344,747	347,720	348,267
Cash, end of period	291,632	305,733	291,632	305,733
SUPPLEMENTAL CASH FLOW INFORMATION:
Income taxes paid (recovered)	42,557	4,754	53,395	9,379
Interest paid	$ 17,846	$ 19,825	$ 22,982	$ 25,042