Segment Information - Statement of earnings by segment (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Segment Reporting Information [Line Items]
Gross premiums written										$ 10,978,925		$ 8,094,926		$ 7,741,135
Net premiums written										7,951,063		5,944,841		6,199,404
Net premiums earned										8,226,425		5,895,070		6,309,521
Net losses and loss expenses										4,882,197	[1]	3,501,356		4,197,166
Acquisition costs										1,317,448	[1]	738,118		909,323
Operating expenses	[2]									1,439,371		1,069,689		957,841
Underwriting profit (loss)										587,409		585,907		245,191
Net investment income	[3]													885,789
Net results from structured products										17,991	[4]	54,209	[5]	23,791	[6]
Net fee income and other	[7]									(13,356)		(6,891)		(5,692)
Loss on sale of life reinsurance subsidiary										0		666,423		0
Extinguishment of debt										5,592		0		0
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments										202,178		107,462		87,777
Net realized and unrealized (gains) losses on derivative instruments										53,123		29,886		7,798
Net income (loss) from investment fund affiliates and operating affiliates										118,060		203,034		258,195
Gain on sale of operating affiliate										340,407		0		0
Exchange (gains) losses										22,504		(37,568)		(28,243)
Corporate operating expenses										480,755		220,165		209,454
Contribution from P&C and Corporate and Other										1,457,199		486,956		1,321,638
Interest expense										163,021		121,221	[8]	107,486	[8]
Non-controlling interests										106,187		80,498		76,731
Provision (benefit) for income tax										(19,161)		96,897		77,505
Net income (loss) attributable to ordinary shareholders										1,207,152		188,340		1,059,916
Exclude Life Funds Withheld Assets [Member]
Segment Reporting Information [Line Items]
Net investment income	[3]									624,440		721,016
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments										19,997		122,991
Life Funds Withheld Assets [Member]
Segment Reporting Information [Line Items]
Net investment income										187,489		129,575
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments										182,181		(15,529)
Net realized and unrealized (gains) losses on derivative instruments										(151,691)		(488,222)		0
Corporate and other
Segment Reporting Information [Line Items]
Gross premiums written	[9]									309,916		333,436		324,343
Net premiums written	[9]									62,239		177,632		295,422
Net premiums earned	[9]									62,241		177,632		295,422
Net losses and loss expenses	[9]									115,997	[1]	242,963		465,702
Acquisition costs	[9]									10,794	[1]	14,115		26,665
Operating expenses	[2],[9]									1,232		10,693		8,926
Underwriting profit (loss)	[9]									(65,782)		(90,139)		(205,871)
Net investment income	[3],[9]													286,645
Net results from structured products	[9]									0	[4]	0	[5]	0	[6]
Net fee income and other	[7],[9]									622		360		1,305
Loss on sale of life reinsurance subsidiary	[9]											666,423
Extinguishment of debt	[9]									5,592
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments	[9]													1,985
Net realized and unrealized (gains) losses on derivative instruments	[9]									53,123		29,886		7,798
Net income (loss) from investment fund affiliates and operating affiliates	[9]									118,060		203,034		258,195
Gain on sale of operating affiliate										340,407
Exchange (gains) losses	[9]									22,504		(37,568)		(28,243)
Corporate operating expenses	[9]									480,755		220,165		209,454
Contribution from P&C and Corporate and Other	[9]									201,538		(929,872)		168,846
Interest expense	[8],[9]									163,021		121,221		107,486
Non-controlling interests	[9]									106,187		80,498		76,731
Provision (benefit) for income tax	[9]									(19,161)		96,897		77,505
Corporate and other | Exclude Life Funds Withheld Assets [Member]
Segment Reporting Information [Line Items]
Net investment income	[3],[9]									40,569		146,558
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments	[9]									5,411		3,625
Corporate and other | Life Funds Withheld Assets [Member]
Segment Reporting Information [Line Items]
Net investment income										187,489	[9]	129,575
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments	[9]									182,181		(15,529)
Net realized and unrealized (gains) losses on derivative instruments	[9]									(151,691)		(488,222)
Operating Segments [Member] | Total P And C Segment [Member]
Segment Reporting Information [Line Items]
Gross premiums written										10,669,009		7,761,490		7,416,792
Net premiums written										7,888,824		5,767,209		5,903,982
Net premiums earned		$ 2,375,155	$ 2,405,740	$ 2,063,795	$ 1,319,494	$ 1,413,161	$ 1,453,673	$ 1,438,076	$ 1,412,528	8,164,184		5,717,438		6,014,099
Net losses and loss expenses										4,766,200	[1]	3,258,393		3,731,464
Acquisition costs										1,306,654	[1]	724,003		882,658
Operating expenses	[2]									1,438,139		1,058,996		948,915
Underwriting profit (loss)		$ 183,458	$ 114,118	$ 208,779	$ 146,836	$ 218,850	$ 144,375	$ 167,947	$ 144,874	653,191		676,046		451,062
Net investment income	[3]													599,144
Net results from structured products										17,991	[4]	54,209	[5]	23,791	[6]
Net fee income and other	[7]									(13,978)		(7,251)		(6,997)
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments														85,792
Net realized and unrealized (gains) losses on derivative instruments										0				0
Contribution from P&C and Corporate and Other										$ 1,255,661		$ 1,416,828		$ 1,152,792
Ratios - P&C operations:
Loss and loss expense ratio	[10]									58.40%		57.00%		62.00%
Underwriting expense ratio	[10]									33.60%		31.20%		30.50%
Combined ratio	[10]									92.00%		88.20%		92.50%
Operating Segments [Member] | Total P And C Segment [Member] | Exclude Life Funds Withheld Assets [Member]
Segment Reporting Information [Line Items]
Net investment income	[3]									$ 583,871		$ 574,458
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments										14,586		119,366
Operating Segments [Member] | Insurance Segment [Member]
Segment Reporting Information [Line Items]
Gross premiums written										8,395,846		5,976,011		$ 5,523,181
Net premiums written										5,859,934		4,134,151		4,154,093
Net premiums earned										5,648,482		4,026,713		4,267,677
Net losses and loss expenses										3,614,048	[1]	2,543,108		2,829,999
Acquisition costs										704,364	[1]	393,319		529,270
Operating expenses	[2]									1,154,760		865,592		782,677
Underwriting profit (loss)										175,310		224,694		125,731
Net results from structured products										12,185	[4]	43,710	[5]	15,562	[6]
Net fee income and other	[7]									$ (16,936)		$ (10,051)		$ (9,317)
Ratios - P&C operations:
Loss and loss expense ratio	[10]									64.00%		63.20%		66.30%
Underwriting expense ratio	[10]									32.90%		31.20%		30.80%
Combined ratio	[10]									96.90%		94.40%		97.10%
Operating Segments [Member] | Reinsurance Segment [Member]
Segment Reporting Information [Line Items]
Gross premiums written										$ 2,273,163		$ 1,785,479		$ 1,893,611
Net premiums written										2,028,890		1,633,058		1,749,889
Net premiums earned										2,515,702		1,690,725		1,746,422
Net losses and loss expenses										1,152,152	[1]	715,285		901,465
Acquisition costs										602,290	[1]	330,684		353,388
Operating expenses	[2]									283,379		193,404		166,238
Underwriting profit (loss)										477,881		451,352		325,331
Net results from structured products										5,806	[4]	10,499	[5]	8,229	[6]
Net fee income and other	[7]									$ 2,958		$ 2,800		$ 2,320
Ratios - P&C operations:
Loss and loss expense ratio	[10]									45.80%		42.30%		51.60%
Underwriting expense ratio	[10]									35.20%		31.00%		29.80%
Combined ratio	[10]									81.00%		73.30%		81.40%

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

[4] The net results from P&C structured products include net investment income and interest expense of $60.4 million and $42.2 million, respectively.

[5] The net results from P&C structured products include net investment income and interest expense of $68.0 million and $12.9 million, respectively.

[6] The net results from P&C structured products include net investment income and interest expense of $71.9 million and $48.0 million, respectively.

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

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

[9] 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.

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