Segment Information - Statement of earnings by segment (Details) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2015		Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014
Segment Reporting Information [Line Items]
Gross premiums written		$ 2,739,350		$ 1,684,198		$ 8,375,845		$ 6,395,373
Net premiums written		2,091,028		1,233,985		6,060,608		4,721,680
Net premiums earned		2,423,552		1,473,412		5,839,605		4,458,845
Net losses and loss expenses		1,486,864	[1]	879,689		3,449,354	[1]	2,737,960
Acquisition costs		409,173	[1]	182,882		904,486	[1]	566,915
Operating expenses	[2]	422,867		271,703		1,038,579		782,526
Underwriting profit (loss)		104,648		139,138		447,186		371,444
Net results from structured products		4,437	[3]	5,291	[4]	14,719	[5]	48,129	[6]
Net fee income and other	[7]	(4,420)		(3,058)		(12,292)		(6,410)
Loss on sale of life reinsurance subsidiary		0		0		0		666,423
Net realized gains (losses) on investments		51,407		4,341		154,265		96,267
Net realized and unrealized gains (losses) on derivative instruments		(7,903)		5,131		57,127		18,540
Net income (loss) from investment fund affiliates and operating affiliates	[8]	4,481		44,521		103,317		169,530
Gain on sale of operating affiliate		0		0		340,407		0
Exchange (gains) losses		11,661		(23,348)		49,425		8,234
Corporate operating expenses		135,500		55,322		328,930		163,155
Contribution from P&C and Corporate and Other		88,927		171,727		1,220,212		280,736
Interest expense	[9]	40,798		31,703		121,317		96,147
Non-controlling interests		57,889		37,583		100,158		77,024
Income tax		(37,042)		30,057		20,135		58,724
Net income (loss) attributable to ordinary shareholders		27,282		72,384		978,602		48,841
Corporate and Other
Segment Reporting Information [Line Items]
Gross premiums written	[10]	80,208		83,496		234,602		254,503
Net premiums written	[10]	17,812		19,739		50,576		154,568
Net premiums earned	[10]	17,812		19,739		50,576		154,568
Net losses and loss expenses	[10]	22,579	[1]	20,101		64,047	[1]	218,987
Acquisition costs	[10]	4,729	[1]	2,090		8,230	[1]	13,151
Operating expenses	[2],[10]	(26)		2,785		846		8,182
Underwriting profit (loss)	[10]	(9,470)		(5,237)		(22,547)		(85,752)
Net results from structured products	[10]	0	[3]	0	[4]	0	[5]	0	[6]
Net fee income and other	[7],[10]	254		167		432		257
Loss on sale of life reinsurance subsidiary	[10]							666,423
Net realized and unrealized gains (losses) on derivative instruments	[10]	(7,903)		5,131		57,127		18,540
Net income (loss) from investment fund affiliates and operating affiliates	[8],[10]	4,481		44,521		103,317		169,530
Gain on sale of operating affiliate	[10]					340,407
Exchange (gains) losses	[10]	11,661		(23,348)		49,425		8,234
Corporate operating expenses	[10]	135,500		55,322		328,930		163,155
Contribution from P&C and Corporate and Other	[10]	(177,495)		(125,707)		303,644		(753,168)
Interest expense	[9],[10]	40,798		31,703		121,317		96,147
Non-controlling interests	[10]	57,889		37,583		100,158		77,024
Income tax	[10]	(37,042)		30,057		20,135		58,724
Excluding Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income	[11]	162,992		153,127		466,302		564,219
Net realized gains (losses) on investments		(201)		9,813		8,752		109,886
Excluding Life Funds Withheld Assets | Corporate and Other
Segment Reporting Information [Line Items]
Net investment income	[10],[11]	10,254		11,552		31,295		134,562
Net realized gains (losses) on investments	[10]	(4)		395		(1,081)		4,297
Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income		46,586		56,474		143,869		75,639
Net realized gains (losses) on investments		51,608		(5,472)		145,513		(13,619)
Net realized and unrealized gains (losses) on derivative instruments		(126,140)		(201,264)		(116,333)		(218,810)
Life Funds Withheld Assets | Corporate and Other
Segment Reporting Information [Line Items]
Net investment income	[10]	46,586		56,474		143,869		75,639
Net realized gains (losses) on investments	[10]	51,608		(5,472)		145,513		(13,619)
Net realized and unrealized gains (losses) on derivative instruments	[10]	(126,140)		(201,264)		(116,333)		(218,810)
Operating Segments [Member] | Total P&C
Segment Reporting Information [Line Items]
Gross premiums written		2,659,142		1,600,702		8,141,243		6,140,870
Net premiums written		2,073,216		1,214,246		6,010,032		4,567,112
Net premiums earned		2,405,740		1,453,673		5,789,029		4,304,277
Net losses and loss expenses		1,464,285	[1]	859,588		3,385,307	[1]	2,518,973
Acquisition costs		404,444	[1]	180,792		896,256	[1]	553,764
Operating expenses	[2]	422,893		268,918		1,037,733		774,344
Underwriting profit (loss)		114,118		144,375		469,733		457,196
Net results from structured products		4,437	[3]	5,291	[4]	14,719	[5]	48,129	[6]
Net fee income and other	[7]	(4,674)		(3,225)		(12,724)		(6,667)
Net realized and unrealized gains (losses) on derivative instruments						0
Contribution from P&C and Corporate and Other		$ 266,422		$ 297,434		$ 916,568		$ 1,033,904
Ratios - P&C operations
Loss and loss expense ratio	[12]	60.90%		59.10%		58.50%		58.50%
Underwriting expense ratio	[12]	34.40%		31.00%		33.40%		30.90%
Combined ratio	[12]	95.30%		90.10%		91.90%		89.40%
Operating Segments [Member] | Insurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		$ 2,200,196		$ 1,324,418		$ 6,074,387		$ 4,513,749
Net premiums written		1,664,562		956,185		4,155,442		3,080,432
Net premiums earned		1,632,988		1,018,416		4,008,200		3,014,846
Net losses and loss expenses		1,037,727	[1]	650,256		2,551,044	[1]	1,917,076
Acquisition costs		214,773	[1]	95,992		476,876	[1]	300,855
Operating expenses	[2]	334,211		218,281		834,829		635,264
Underwriting profit (loss)		46,277		53,887		145,451		161,651
Net results from structured products		3,328	[3]	3,571	[4]	9,634	[5]	40,106	[6]
Net fee income and other	[7]	$ (5,207)		$ (3,826)		$ (14,705)		$ (8,605)
Ratios - P&C operations
Loss and loss expense ratio	[12]	63.50%		63.80%		63.60%		63.60%
Underwriting expense ratio	[12]	33.70%		30.90%		32.80%		31.00%
Combined ratio	[12]	97.20%		94.70%		96.40%		94.60%
Operating Segments [Member] | Reinsurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		$ 458,946		$ 276,284		$ 2,066,856		$ 1,627,121
Net premiums written		408,654		258,061		1,854,590		1,486,680
Net premiums earned		772,752		435,257		1,780,829		1,289,431
Net losses and loss expenses		426,558	[1]	209,332		834,263	[1]	601,897
Acquisition costs		189,671	[1]	84,800		419,380	[1]	252,909
Operating expenses	[2]	88,682		50,637		202,904		139,080
Underwriting profit (loss)		67,841		90,488		324,282		295,545
Net results from structured products		1,109	[3]	1,720	[4]	5,085	[5]	8,023	[6]
Net fee income and other	[7]	$ 533		$ 601		$ 1,981		$ 1,938
Ratios - P&C operations
Loss and loss expense ratio	[12]	55.20%		48.10%		46.80%		46.70%
Underwriting expense ratio	[12]	36.00%		31.10%		35.00%		30.40%
Combined ratio	[12]	91.20%		79.20%		81.80%		77.10%
Operating Segments [Member] | Excluding Life Funds Withheld Assets | Total P&C
Segment Reporting Information [Line Items]
Net investment income	[11]	$ 152,738		$ 141,575		$ 435,007		$ 429,657
Net realized gains (losses) on investments		$ (197)		$ 9,418		$ 9,833		$ 105,589

[1] The Company has reflected the amortization of certain fair value adjustments recorded in conjunction with the Catlin Acquisition within the respective segments.

[2] Operating expenses of the segments exclude Corporate operating expenses, shown separately.

[3] The net results from P&C structured products include net investment income and interest expense of $15.6 million and $11.1 million, respectively.

[4] The net results from P&C structured products include net investment income and interest credit of $16.8 million and $11.1 million, respectively.

[5] The net results from P&C structured products include net investment income and interest expense of $46.7 million and $31.7 million, respectively.

[6] The net results from P&C structured products include net investment income and interest credit of $52.5 million and $3.7 million, respectively.

[7] Net fee income and other includes operating expenses from the Company's loss prevention consulting services business.

[8] The Company generally records the income related to the hedge fund affiliates and to the private investment and operating fund affiliates on a one-month and three-month lag, respectively.

[9] Interest expense excludes interest expense related to deposit liabilities recorded in the Insurance and Reinsurance segments

[10] Corporate and Other includes other items of our revenues and expenditures that are not evaluated at the segment level for reporting purposes, as well as the Company's Run-Off Life Operations.

[11] Net investment income - excluding Life Funds Withheld Assets does not include net investment income related to the net results from structured products.

[12] Ratios are based on net premiums earned from P&C operations.