Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 107,572	$ 301,253	$ 682,114	$ 901,200
Adjustments to reconcile net income to net cash provided by operating activities:
Decrease (increase) in premiums receivable			(274,198)	(255,645)
Decrease (increase) in funds held by reinsureds, net			33,255	(6,929)
Decrease (increase) in reinsurance receivables			(202,329)	(256,458)
Decrease (increase) in income taxes			(61,627)	(14,696)
Decrease (increase) in prepaid reinsurance premiums			(46,633)	(101,478)
Increase (decrease) in reserve for losses and loss adjustment expenses			347,729	172,511
Increase (decrease) in future policy benefit reserve			(240)	(1,879)
Increase (decrease) in unearned premiums			1,455	255,537
Increase (decrease) in other net payable to reinsurers			67,550	101,984
Increase (decrease) in losses in course of payment			142,418	165,105
Change in equity adjustments in limited partnerships			(12,725)	(24,438)
Distribution of limited partnership income			42,625	41,165
Change in other assets and liabilities, net			18,573	(32,114)
Non-cash compensation expense			16,150	14,720
Amortization of bond premium (accrual of bond discount)			38,770	38,010
Amortization of underwriting discount on senior notes			3	43
Net realized capital (gains) losses	159,971	9,448	194,654	(70,694)
Net cash provided by (used in) operating activities			987,544	925,944
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from fixed maturities matured/called - available for sale, at market value			1,687,589	1,638,278
Proceeds from fixed maturities matured/called - available for sale, at fair value				875
Proceeds from fixed maturities sold - available for sale, at market value			1,146,000	1,050,082
Proceeds from fixed maturities sold - available for sale, at fair value			1,824	23,856
Proceeds from equity securities sold - available for sale, at market value			22,120	11,174
Proceeds from equity securities sold - available for sale, at fair value			439,692	452,514
Distributions from other invested assets			41,782	59,264
Proceeds from sale of subsidiary (net of cash disposed)			3,934
Cost of fixed maturities acquired - available for sale, at market value			(3,583,990)	(3,729,423)
Cost of fixed maturities acquired - available for sale, at fair value			(234)	(23,684)
Cost of equity securities acquired - available for sale, at market value			(6,581)	(11,873)
Cost of equity securities acquired - available for sale, at fair value			(460,965)	(262,871)
Cost of other invested assets acquired			(140,923)	(120,911)
Net change in short-term investments			83,584	(284,822)
Net change in unsettled securities transactions			(18,242)	13,496
Net cash provided by (used in) investing activities			(784,410)	(1,184,045)
CASH FLOWS FROM FINANCING ACTIVITIES:
Common shares issued during the period, net			9,896	15,465
Purchase of treasury shares			(324,981)	(399,942)
Net proceeds from issuance of senior notes				400,000
Third party investment in redeemable noncontrolling interest			296,848	136,200
Dividends paid to shareholders			(125,905)	(103,034)
Dividends paid on third party investment in redeemable noncontrolling interest			(67,233)	(10,334)
Net cash provided by (used in) financing activities			(211,375)	38,355
EFFECT OF EXCHANGE RATE CHANGES ON CASH			(28,007)	10,167
Net increase (decrease) in cash			(36,248)	(209,579)
Cash, beginning of period			437,474	611,382	$ 611,382
Cash, end of period	$ 401,226	$ 401,803	401,226	401,803	$ 437,474
SUPPLEMENTAL CASH FLOW INFORMATION:
Income taxes paid (recovered)			123,234	146,560
Interest paid			$ 18,039	$ 15,150