Segment Information - Statement of earnings by segment (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Gross premiums written		$ 2,783,603	$ 2,739,350	$ 10,811,152	$ 8,375,845
Net premiums written		2,135,658	2,091,028	7,926,536	6,060,608
Net premiums earned		2,434,037	2,423,552	7,320,859	5,839,605
Net losses and loss expenses	[1]	1,497,678	1,486,864	4,522,968	3,449,354
Acquisition costs	[1]	403,888	409,173	1,227,675	904,486
Operating expenses	[2]	370,279	422,867	1,138,296	1,038,579
Underwriting profit (loss)		162,192	104,648	431,920	447,186
Net results from structured products	[3]	7,708	4,437	11,737	14,719
Net fee income and other	[4]	(3,271)	(4,420)	(8,324)	(12,292)
Loss (gain) on sale of subsidiary		(3,670)	0	(3,670)	0
Net realized gains (losses) on investments		143,676	51,407	341,043	154,265
Net realized and unrealized gains (losses) on derivative instruments		5,490	(7,903)	2,774	57,127
Net income (loss) from investment fund affiliates and operating affiliates		24,566	4,481	67,234	103,317
Gain on sale of operating affiliate		0	0	0	340,407
Exchange (gains) losses		(1,695)	11,661	(54,614)	49,425
Corporate operating expenses		126,308	135,500	372,003	328,930
Contribution from P&C and Corporate and Other		189,451	88,927	431,413	1,220,212
Interest expense	[5]	43,025	40,798	128,371	121,317
Non-controlling interests		58,076	57,889	124,263	100,158
Income tax		17,749	(37,042)	42,511	20,135
Net income (loss) attributable to ordinary shareholders		70,601	27,282	136,268	978,602
Corporate and Other
Segment Reporting Information [Line Items]
Gross premiums written	[6]	64,683	80,208	202,139	234,602
Net premiums written	[6]	2,360	17,812	9,032	50,576
Net premiums earned	[6]	2,360	17,812	9,032	50,576
Net losses and loss expenses	[1],[6]	5,875	22,579	16,294	64,047
Acquisition costs	[1],[6]	1,002	4,729	4,286	8,230
Operating expenses	[2],[6]	142	(26)	765	846
Underwriting profit (loss)	[6]	(4,659)	(9,470)	(12,313)	(22,547)
Net results from structured products	[3],[6]	0	0	0	0
Net fee income and other	[4],[6]	595	254	1,068	432
Loss (gain) on sale of subsidiary		(3,670)		(3,670)
Net realized and unrealized gains (losses) on derivative instruments	[6]	5,490	(7,903)	2,774	57,127
Net income (loss) from investment fund affiliates and operating affiliates	[6]	24,566	4,481	67,234	103,317
Gain on sale of operating affiliate	[6]				340,407
Exchange (gains) losses	[6]	(1,695)	11,661	(54,614)	49,425
Corporate operating expenses	[6]	126,308	135,500	372,003	328,930
Contribution from P&C and Corporate and Other	[6]	(190,290)	(177,495)	(538,703)	303,644
Interest expense	[5],[6]	43,025	40,798	128,371	121,317
Non-controlling interests	[6]	58,076	57,889	124,263	100,158
Income tax	[6]	17,749	(37,042)	42,511	20,135
Excluding Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income	[7]	156,706	162,992	470,537	466,302
Net realized gains (losses) on investments		58,395	(201)	69,447	8,752
Excluding Life Funds Withheld Assets | Corporate and Other
Segment Reporting Information [Line Items]
Net investment income	[6],[7]	8,127	10,254	24,185	31,295
Net realized gains (losses) on investments	[6]	(2,006)	(4)	(7,742)	(1,081)
Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income		38,937	46,586	119,643	143,869
Net realized gains (losses) on investments		85,281	51,608	271,596	145,513
Net realized and unrealized gains (losses) on derivative instruments		(225,610)	(126,140)	(691,432)	(116,333)
Life Funds Withheld Assets | Corporate and Other
Segment Reporting Information [Line Items]
Net investment income	[6]	38,937	46,586	119,643	143,869
Net realized gains (losses) on investments	[6]	85,213	51,608	271,599	145,513
Net realized and unrealized gains (losses) on derivative instruments	[6]	(225,610)	(126,140)	(691,432)	(116,333)
Life Funds Withheld Assets | Total P&C
Segment Reporting Information [Line Items]
Net realized gains (losses) on investments		68	0	(3)
Operating Segments [Member] | Total P&C
Segment Reporting Information [Line Items]
Gross premiums written		2,718,920	2,659,142	10,609,013	8,141,243
Net premiums written		2,133,298	2,073,216	7,917,504	6,010,032
Net premiums earned		2,431,677	2,405,740	7,311,827	5,789,029
Net losses and loss expenses	[1]	1,491,803	1,464,285	4,506,674	3,385,307
Acquisition costs	[1]	402,886	404,444	1,223,389	896,256
Operating expenses	[2]	370,137	422,893	1,137,531	1,037,733
Underwriting profit (loss)		166,851	114,118	444,233	469,733
Net results from structured products	[3]	7,708	4,437	11,737	14,719
Net fee income and other	[4]	(3,866)	(4,674)	(9,392)	(12,724)
Net realized and unrealized gains (losses) on derivative instruments		0	0	0
Contribution from P&C and Corporate and Other		$ 379,741	$ 266,422	$ 970,116	$ 916,568
Ratios - P&C operations
Loss and loss expense ratio	[8]	61.30%	60.90%	61.60%	58.50%
Underwriting expense ratio	[8]	31.80%	34.40%	32.30%	33.40%
Combined ratio	[8]	93.10%	95.30%	93.90%	91.90%
Operating Segments [Member] | Insurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		$ 2,153,379	$ 2,200,196	$ 7,169,363	$ 6,074,387
Net premiums written		1,615,132	1,664,562	4,899,258	4,155,442
Net premiums earned		1,653,461	1,632,988	4,944,055	4,008,200
Net losses and loss expenses	[1]	1,068,268	1,037,727	3,163,599	2,551,044
Acquisition costs	[1]	221,137	214,773	679,009	476,876
Operating expenses	[2]	302,373	334,211	922,273	834,829
Underwriting profit (loss)		61,683	46,277	179,174	145,451
Net results from structured products	[3]	2,353	3,328	6,340	9,634
Net fee income and other	[4]	$ (4,486)	$ (5,207)	$ (12,097)	$ (14,705)
Ratios - P&C operations
Loss and loss expense ratio	[8]	64.60%	63.50%	64.00%	63.60%
Underwriting expense ratio	[8]	31.70%	33.70%	32.40%	32.80%
Combined ratio	[8]	96.30%	97.20%	96.40%	96.40%
Operating Segments [Member] | Reinsurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		$ 565,541	$ 458,946	$ 3,439,650	$ 2,066,856
Net premiums written		518,166	408,654	3,018,246	1,854,590
Net premiums earned		778,216	772,752	2,367,772	1,780,829
Net losses and loss expenses	[1]	423,535	426,558	1,343,075	834,263
Acquisition costs	[1]	181,749	189,671	544,380	419,380
Operating expenses	[2]	67,764	88,682	215,258	202,904
Underwriting profit (loss)		105,168	67,841	265,059	324,282
Net results from structured products	[3]	5,355	1,109	5,397	5,085
Net fee income and other	[4]	$ 620	$ 533	$ 2,705	$ 1,981
Ratios - P&C operations
Loss and loss expense ratio	[8]	54.40%	55.20%	56.70%	46.80%
Underwriting expense ratio	[8]	32.10%	36.00%	32.10%	35.00%
Combined ratio	[8]	86.50%	91.20%	88.80%	81.80%
Operating Segments [Member] | Excluding Life Funds Withheld Assets | Total P&C
Segment Reporting Information [Line Items]
Net investment income	[7]	$ 148,579	$ 152,738	$ 446,352	$ 435,007
Net realized gains (losses) on investments		$ 60,401	$ (197)	$ 77,189	$ 9,833

[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 $40.9 million and $29.1 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.