Segment Information - Statement of earnings by segment (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016		Mar. 31, 2015
Segment Reporting Information [Line Items]
Gross premiums written		$ 4,428,226		$ 2,555,360
Net premiums written		3,064,759		1,851,249
Net premiums earned		2,354,610		1,334,000
Net losses and loss expenses		1,387,422	[1]	789,214
Acquisition costs		403,267	[1]	153,696
Operating expenses		391,884	[2]	251,883
Underwriting profit (loss)		172,037		139,207
Net results from structured products		1,970	[3]	5,025
Net fee income and other		(2,723)	[4]	(6,508)
Loss on sale of life reinsurance subsidiary				0
Net realized gains (losses) on investments		92,750		52,891
Net realized and unrealized gains (losses) on derivative instruments		(3,622)		16,521
Net income (loss) from investment fund affiliates and operating affiliates		8,071		57,997
Gain on sale of operating affiliate		0
Exchange (gains) losses		(33,819)		27,390
Corporate operating expenses		112,510		62,443
Contribution from P&C and Corporate and Other		146,936		139,370
Interest expense		41,613	[5]	41,481
Non-controlling interests		61,143		37,390
Income tax		22,295		24,218
Net income (loss) attributable to ordinary shareholders		21,885		36,281
Corporate and Other
Segment Reporting Information [Line Items]
Gross premiums written		68,911	[6]	74,951
Net premiums written		3,164	[6]	14,506
Net premiums earned		3,164	[6]	14,506
Net losses and loss expenses		4,937	[1],[6]	19,387
Acquisition costs		1,461	[1],[6]	1,817
Operating expenses		218	[2],[6]	931
Underwriting profit (loss)		(3,452)	[6]	(7,629)
Net results from structured products		0	[3],[6]	0
Net fee income and other		302	[4],[6]	132
Loss on sale of life reinsurance subsidiary				0
Net realized and unrealized gains (losses) on derivative instruments		(3,622)	[6]	16,521
Net income (loss) from investment fund affiliates and operating affiliates		8,071	[6]	57,997
Gain on sale of operating affiliate	[6]	0
Exchange (gains) losses		(33,819)	[6]	27,390
Corporate operating expenses		112,510	[6]	62,443
Contribution from P&C and Corporate and Other		(159,469)	[6]	(144,466)
Interest expense		41,613	[5],[6]	41,481
Non-controlling interests		61,143	[6]	37,390
Income tax		22,295	[6]	24,218
Excluding Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income		151,664	[7]	143,018
Net realized gains (losses) on investments		(8,416)		4,602
Excluding Life Funds Withheld Assets | Corporate and Other
Segment Reporting Information [Line Items]
Net investment income		8,533	[6],[7]	10,210
Net realized gains (losses) on investments		2,744	[6]	(1,205)
Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income		41,560		50,419
Net realized gains (losses) on investments		101,166		48,289
Net realized and unrealized gains (losses) on derivative instruments		(236,080)		(229,367)
Life Funds Withheld Assets | Corporate and Other
Segment Reporting Information [Line Items]
Net investment income		41,560	[6]	50,419
Net realized gains (losses) on investments		101,166	[6]	48,289
Net realized and unrealized gains (losses) on derivative instruments		(236,080)	[6]	(229,367)
Life Funds Withheld Assets | Total P&C
Segment Reporting Information [Line Items]
Net realized gains (losses) on investments		0
Operating Segments [Member] | Total P&C
Segment Reporting Information [Line Items]
Gross premiums written		4,359,315		2,480,409
Net premiums written		3,061,595		1,836,743
Net premiums earned		2,351,446		1,319,494
Net losses and loss expenses		1,382,485	[1]	769,827
Acquisition costs		401,806	[1]	151,879
Operating expenses		391,666	[2]	250,952
Underwriting profit (loss)		175,489		146,836
Net results from structured products		1,970	[3]	5,025
Net fee income and other		(3,025)	[4]	(6,640)
Net realized and unrealized gains (losses) on derivative instruments		0
Contribution from P&C and Corporate and Other		$ 306,405		$ 283,836
Ratios - P&C operations
Loss and loss expense ratio		58.80%	[8]	58.30%
Underwriting expense ratio		33.70%	[8]	30.60%
Combined ratio		92.50%	[8]	88.90%
Operating Segments [Member] | Insurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		$ 2,503,972		$ 1,654,747
Net premiums written		1,503,934		1,089,108
Net premiums earned		1,593,874		962,306
Net losses and loss expenses		999,592	[1]	616,947
Acquisition costs		225,458	[1]	80,387
Operating expenses		312,432	[2]	208,457
Underwriting profit (loss)		56,392		56,515
Net results from structured products		1,222	[3]	2,905
Net fee income and other		$ (3,862)	[4]	$ (7,465)
Ratios - P&C operations
Loss and loss expense ratio		62.70%	[8]	64.10%
Underwriting expense ratio		33.80%	[8]	30.00%
Combined ratio		96.50%	[8]	94.10%
Operating Segments [Member] | Reinsurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		$ 1,855,343		$ 825,662
Net premiums written		1,557,661		747,635
Net premiums earned		757,572		357,188
Net losses and loss expenses		382,893	[1]	152,880
Acquisition costs		176,348	[1]	71,492
Operating expenses		79,234	[2]	42,495
Underwriting profit (loss)		119,097		90,321
Net results from structured products		748	[3]	2,120
Net fee income and other		$ 837	[4]	$ 825
Ratios - P&C operations
Loss and loss expense ratio		50.50%	[8]	42.80%
Underwriting expense ratio		33.80%	[8]	31.90%
Combined ratio		84.30%	[8]	74.70%
Operating Segments [Member] | Excluding Life Funds Withheld Assets | Total P&C
Segment Reporting Information [Line Items]
Net investment income		$ 143,131	[7]	$ 132,808
Net realized gains (losses) on investments		$ (11,160)		$ 5,807

[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 $12.7 million and $10.7 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.