Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 235,472	$ 297,925	$ 574,542	$ 599,947
Adjustments to reconcile net income to net cash provided by operating activities:
Decrease (increase) in premiums receivable			(51,422)	(97,827)
Decrease (increase) in funds held by reinsureds, net			68,245	2,148
Decrease (increase) in reinsurance receivables			(32,526)	(137,077)
Decrease (increase) in income taxes			(20,898)	15,257
Decrease (increase) in prepaid reinsurance premiums			(28,916)	(68,346)
Increase (decrease) in reserve for losses and loss adjustment expenses			113,567	8,055
Increase (decrease) in future policy benefit reserve			(364)	(1,144)
Increase (decrease) in unearned premiums			(160,849)	96,803
Increase (decrease) in other net payable to reinsurers			23,867	100,546
Increase (decrease) in losses in course of payment			95,003	161,990
Change in equity adjustments in limited partnerships			(12,840)	(3,200)
Distribution of limited partnership income			18,332	13,430
Change in other assets and liabilities, net			26,768	(56,872)
Non-cash compensation expense			10,364	9,768
Amortization of bond premium (accrual of bond discount)			25,514	27,068
Amortization of underwriting discount on senior notes			2	28
Net realized capital (gains) losses	24,178	(59,016)	34,683	(80,142)
Net cash provided by (used in) operating activities			683,072	590,432
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from fixed maturities matured/called - available for sale, at market value			1,172,211	1,047,509
Proceeds from fixed maturities matured/called - available for sale, at fair value				875
Proceeds from fixed maturities sold - available for sale, at market value			731,673	606,476
Proceeds from fixed maturities sold - available for sale, at fair value			1,613	20,763
Proceeds from equity securities sold - available for sale, at market value			4,599	8,672
Proceeds from equity securities sold - available for sale, at fair value			300,620	304,892
Distributions from other invested assets			27,705	22,520
Cost of fixed maturities acquired - available for sale, at market value			(2,448,121)	(2,458,723)
Cost of fixed maturities acquired - available for sale, at fair value			(234)	(1,309)
Cost of equity securities acquired - available for sale, at market value			(5,541)	(10,619)
Cost of equity securities acquired - available for sale, at fair value			(317,650)	(183,314)
Cost of other invested assets acquired			(98,890)	(34,388)
Net change in short-term investments			(199,226)	(423,677)
Net change in unsettled securities transactions			4,475	20,633
Net cash provided by (used in) investing activities			(826,766)	(1,079,690)
CASH FLOWS FROM FINANCING ACTIVITIES:
Common shares issued during the period, net			5,468	13,143
Purchase of treasury shares			(124,981)	(324,951)
Net proceeds from issuance of senior notes				400,000
Third party investment in redeemable noncontrolling interest			296,848	123,700
Subscription advances for third party redeemable noncontrolling interest				77,500
Dividends paid to shareholders			(84,207)	(69,061)
Dividends paid on third party investment in redeemable noncontrolling interest			(41,178)
Net cash provided by (used in) financing activities			51,950	220,331
EFFECT OF EXCHANGE RATE CHANGES ON CASH			(6,829)	(885)
Net increase (decrease) in cash			(98,573)	(269,812)
Cash, beginning of period			437,474	611,382	$ 611,382
Cash, end of period	$ 338,901	$ 341,570	338,901	341,570	$ 437,474
SUPPLEMENTAL CASH FLOW INFORMATION:
Income taxes paid (recovered)			93,352	97,241
Interest paid			$ 17,907	$ 15,018