Segment Information - Statement of earnings by segment (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Gross premiums written		$ 3,599,323	$ 3,081,135	$ 8,027,549	$ 5,636,495
Net premiums written		2,726,119	2,118,331	5,790,878	3,969,580
Net premiums earned		2,532,212	2,082,053	4,886,822	3,416,053
Net losses and loss expenses	[1]	1,637,868	1,173,276	3,025,290	1,962,490
Acquisition costs	[1]	420,520	341,617	823,787	495,313
Operating expenses	[2]	376,133	363,829	768,017	615,712
Underwriting profit (loss)		97,691	203,331	269,728	342,538
Net results from structured products	[3]	2,059	5,257	4,029	10,282
Net fee income and other	[4]	(2,330)	(1,364)	(5,053)	(7,872)
Net realized gains (losses) on investments		104,617	49,967	197,367	102,858
Net realized and unrealized gains (losses) on derivative instruments		906	48,509	(2,716)	65,030
Net income (loss) from investment fund affiliates and operating affiliates		34,597	40,839	42,668	98,836
Gain on sale of operating affiliate		0	340,407	0	340,407
Exchange (gains) losses		(19,100)	10,374	(52,919)	37,764
Corporate operating expenses		133,185	130,987	245,695	193,430
Contribution from P&C and Corporate and Other		95,026	991,915	241,962	1,131,285
Interest expense	[5]	43,733	39,038	85,346	80,519
Non-controlling interests		5,044	4,879	66,187	42,269
Income tax		2,467	32,959	24,762	57,177
Net income (loss) attributable to ordinary shareholders		43,782	915,039	65,667	951,320
Corporate and Other
Segment Reporting Information [Line Items]
Gross premiums written	[6]	68,545	79,443	137,456	154,394
Net premiums written	[6]	3,508	18,258	6,672	32,764
Net premiums earned	[6]	3,508	18,258	6,672	32,764
Net losses and loss expenses	[1],[6]	5,482	22,081	10,419	41,468
Acquisition costs	[1],[6]	1,823	1,684	3,284	3,501
Operating expenses	[2],[6]	405	(59)	623	872
Underwriting profit (loss)	[6]	(4,202)	(5,448)	(7,654)	(13,077)
Net results from structured products	[3],[6]	0	0	0	0
Net fee income and other	[4],[6]	171	46	473	178
Net realized and unrealized gains (losses) on derivative instruments	[6]	906	48,509	(2,716)	65,030
Net income (loss) from investment fund affiliates and operating affiliates	[6]	34,597	40,839	42,668	98,836
Gain on sale of operating affiliate	[6]		340,407		340,407
Exchange (gains) losses	[6]	(19,100)	10,374	(52,919)	37,764
Corporate operating expenses	[6]	133,185	130,987	245,695	193,430
Contribution from P&C and Corporate and Other	[6]	(188,944)	625,605	(348,413)	481,139
Interest expense	[5],[6]	43,733	39,038	85,346	80,519
Non-controlling interests	[6]	5,044	4,879	66,187	42,269
Income tax	[6]	2,467	32,959	24,762	57,177
Excluding Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income	[7]	162,167	160,292	313,831	303,310
Net realized gains (losses) on investments		19,468	4,351	11,052	8,953
Excluding Life Funds Withheld Assets | Corporate and Other
Segment Reporting Information [Line Items]
Net investment income	[6],[7]	7,525	10,831	16,058	21,041
Net realized gains (losses) on investments	[6]	(8,480)	128	(5,736)	(1,077)
Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income		39,146	46,864	80,706	97,283
Net realized gains (losses) on investments		85,149	45,616	186,315	93,905
Net realized and unrealized gains (losses) on derivative instruments		(229,742)	239,174	(465,822)	9,807
Life Funds Withheld Assets | Corporate and Other
Segment Reporting Information [Line Items]
Net investment income	[6]	39,146	46,864	80,706	97,283
Net realized gains (losses) on investments	[6]	85,220	45,616	186,386	93,905
Net realized and unrealized gains (losses) on derivative instruments	[6]	(229,742)	239,174	(465,822)	9,807
Life Funds Withheld Assets | Total P&C
Segment Reporting Information [Line Items]
Net realized gains (losses) on investments		(71)	0	(71)
Operating Segments [Member] | Total P&C
Segment Reporting Information [Line Items]
Gross premiums written		3,530,778	3,001,692	7,890,093	5,482,101
Net premiums written		2,722,611	2,100,073	5,784,206	3,936,816
Net premiums earned		2,528,704	2,063,795	4,880,150	3,383,289
Net losses and loss expenses	[1]	1,632,386	1,151,195	3,014,871	1,921,022
Acquisition costs	[1]	418,697	339,933	820,503	491,812
Operating expenses	[2]	375,728	363,888	767,394	614,840
Underwriting profit (loss)		101,893	208,779	277,382	355,615
Net results from structured products	[3]	2,059	5,257	4,029	10,282
Net fee income and other	[4]	(2,501)	(1,410)	(5,526)	(8,050)
Net realized and unrealized gains (losses) on derivative instruments		0	0	0
Contribution from P&C and Corporate and Other		$ 283,970	$ 366,310	$ 590,375	$ 650,146
Ratios - P&C operations
Loss and loss expense ratio	[8]	64.60%	55.80%	61.80%	56.80%
Underwriting expense ratio	[8]	31.40%	34.10%	32.50%	32.70%
Combined ratio	[8]	96.00%	89.90%	94.30%	89.50%
Operating Segments [Member] | Insurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		$ 2,512,012	$ 2,219,444	$ 5,015,984	$ 3,874,191
Net premiums written		1,780,192	1,401,772	3,284,126	2,490,880
Net premiums earned		1,696,720	1,412,906	3,290,594	2,375,212
Net losses and loss expenses	[1]	1,095,739	896,370	2,095,331	1,513,317
Acquisition costs	[1]	232,414	181,716	457,872	262,103
Operating expenses	[2]	307,468	292,161	619,900	500,618
Underwriting profit (loss)		61,099	42,659	117,491	99,174
Net results from structured products	[3]	2,765	3,401	3,987	6,306
Net fee income and other	[4]	$ (3,749)	$ (2,033)	$ (7,611)	$ (9,498)
Ratios - P&C operations
Loss and loss expense ratio	[8]	64.60%	63.40%	63.70%	63.70%
Underwriting expense ratio	[8]	31.80%	33.60%	32.70%	32.10%
Combined ratio	[8]	96.40%	97.00%	96.40%	95.80%
Operating Segments [Member] | Reinsurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		$ 1,018,766	$ 782,248	$ 2,874,109	$ 1,607,910
Net premiums written		942,419	698,301	2,500,080	1,445,936
Net premiums earned		831,984	650,889	1,589,556	1,008,077
Net losses and loss expenses	[1]	536,647	254,825	919,540	407,705
Acquisition costs	[1]	186,283	158,217	362,631	229,709
Operating expenses	[2]	68,260	71,727	147,494	114,222
Underwriting profit (loss)		40,794	166,120	159,891	256,441
Net results from structured products	[3]	(706)	1,856	42	3,976
Net fee income and other	[4]	$ 1,248	$ 623	$ 2,085	$ 1,448
Ratios - P&C operations
Loss and loss expense ratio	[8]	64.50%	39.20%	57.80%	40.40%
Underwriting expense ratio	[8]	30.60%	35.30%	32.10%	34.20%
Combined ratio	[8]	95.10%	74.50%	89.90%	74.60%
Operating Segments [Member] | Excluding Life Funds Withheld Assets | Total P&C
Segment Reporting Information [Line Items]
Net investment income	[7]	$ 154,642	$ 149,461	$ 297,773	$ 282,269
Net realized gains (losses) on investments		$ 27,948	$ 4,223	$ 16,788	$ 10,030

[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 $26.7 million and $22.7 million, respectively.

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

[5] Interest expense excludes interest expense related to structured products recorded in the Insurance and Reinsurance segments.

[6] Corporate and Other includes other items of our revenue and expenditures that are not evaluated at the segment level for reporting purposes, as well as the Company's run-off life operations.

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

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