Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 214,724	$ (97,533)
Adjustments to reconcile net income to net cash provided by operating activities:
Decrease (increase) in premiums receivable	37,206	(111,328)
Decrease (increase) in funds held by reinsureds, net	(40,354)	196
Decrease (increase) in reinsurance receivables	7,668	(306,071)
Decrease (increase) in federal income taxes receivable	(898)	(54,380)
Decrease (increase) in deferred tax asset	74,674	34,314
Decrease (increase) in prepaid reinsurance premiums	4,536	23,936
Increase (decrease) in reserve for losses and loss adjustment expenses	(165,989)	465,159
Increase (decrease) in unearned premiums	(10,324)	(23,149)
Increase (decrease) in other net payable to reinsurers	4,105	52,782
Change in equity adjustments in limited partnerships	(11,285)	(18,415)
Change in other assets and liabilities, net	44,382	72,345
Non-cash compensation expense	1,616	1,380
Amortization of bond premium (accrual of bond discount)	4,274	3,492
Amortization of underwriting discount on senior notes	13	12
Net realized capital (gains) losses	(176,141)	(40,476)
Net cash provided by (used in) operating activities	(11,793)	2,264
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from fixed maturities matured/called - available for sale, at market value	202,187	107,455
Proceeds from fixed maturities matured/called - available for sale, at fair value		6,900
Proceeds from fixed maturities sold - available for sale, at market value	84,136	516,721
Proceeds from fixed maturities sold - available for sale, at fair value	59,281	32,952
Proceeds from equity securities sold - available for sale, at market value		27,096
Proceeds from equity securities sold - available for sale, at fair value	239,540	52,696
Distributions from other invested assets	5,861	61,359
Cost of fixed maturities acquired - available for sale, at market value	(292,848)	(472,805)
Cost of fixed maturities acquired - available for sale, at fair value	(3,124)	(8,076)
Cost of equity securities acquired - available for sale, at market value		(27,059)
Cost of equity securities acquired - available for sale, at fair value	(105,214)	(126,665)
Cost of other invested assets acquired	(11,636)	(23,014)
Cost of other invested assets acquired, at fair value		(37,611)
Cost of businesses acquired		(63,100)
Net change in short-term investments	(222,137)	149,303
Net change in unsettled securities transactions	29,769	(143,998)
Net cash provided by (used in) investing activities	(14,185)	52,154
CASH FLOWS FROM FINANCING ACTIVITIES:
Tax benefit from share-based compensation	10	209
Revolving credit borrowings		(10,000)
Net cash provided by (used in) financing activities	10	(9,791)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	22,448	6,646
Net increase (decrease) in cash	(3,520)	51,273
Cash, beginning of period	348,267	118,092
Cash, end of period	344,747	169,365
SUPPLEMENTAL CASH FLOW INFORMATION:
Income taxes paid (recovered)	4,625	10,792
Interest paid	5,217	5,203
Non-cash transaction:
Net assets acquired and liabilities assumed from business acquisitions		$ 19,130