FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2011

Fair Value, by Balance Sheet Grouping [Table Text Block]

December 31, 2011 (U.S. dollars in thousands)	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Collateral and Counterparty Netting			Balance at December 31, 2011
Assets
U.S. Government and Government-Related/Supported	$	—	$	1,990,983	$	—	$	—		$	1,990,983
Corporate (1)		—		10,438,697		23,818		—			10,462,515
Residential mortgage-backed securities – Agency		—		5,347,365		32,041		—			5,379,406
Residential mortgage-backed securities – Non-Agency		—		641,815		—		—			641,815
Commercial mortgage-backed securities		—		974,835		—		—			974,835
Collateralized debt obligations		—		7,751		650,851		—			658,602
Other asset-backed securities		—		969,804		16,552		—			986,356
U.S. States and political subdivisions of the States		—		1,797,378		—		—			1,797,378
Non-U.S. Sovereign Government, Supranational and Government-Related		—		3,298,135		—		—			3,298,135
Total fixed maturities, at fair value	$	—	$	25,466,763	$	723,262	$	—		$	26,190,025
Equity securities, at fair value (2)		239,175		229,022		—		—			468,197
Short-term investments, at fair value (1) (3)		—		359,063		—		—			359,063
Total investments available for sale	$	239,175	$	26,054,848	$	723,262	$	—		$	27,017,285
Cash equivalents (4)		1,686,101		1,068,264				—			2,754,365
Other investments (5)		—		547,598		113,959		—			661,557
Other assets (6)(7)		—		143,622		—		(77,888	)		65,734
Total assets accounted for at fair value	$	1,925,276	$	27,814,332	$	837,221	$	(77,888	)	$	30,498,941
Liabilities
Financial instruments sold, but not yet purchased (8)	$	—	$	20,844	$	—	$	—		$	20,844
Other liabilities (6)(7)		—		16,871		42,644		(809	)		58,706
Total liabilities accounted for at fair value	$	—	$	37,715	$	42,644	$	(809	)	$	79,550

December 31, 2010 (U.S. dollars in thousands)	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Collateral and Counterparty Netting			Balance at December 31, 2010
Assets
U.S. Government and Government-Related/Supported	$	—	$	2,565,444	$	—	$	—		$	2,565,444
Corporate (1)		—		10,932,105		36,866		—			10,968,971
Residential mortgage-backed securities – Agency		—		5,173,456		30,255		—			5,203,711
Residential mortgage-backed securities – Non-Agency		—		1,016,859		4,964		—			1,021,823
Commercial mortgage-backed securities		—		1,170,884		1,623		—			1,172,507
Collateralized debt obligations		—		12,566		721,572		—			734,138
Other asset-backed securities		—		935,882		24,650		—			960,532
U.S. States and political subdivisions of the States		—		1,360,456		—		—			1,360,456
Non-U.S. Sovereign Government, Supranational and Government-Related		—		3,150,856		3,667		—			3,154,523
Total fixed maturities, at fair value	$	—	$	26,318,508	$	823,597	$	—		$	27,142,105
Equity securities, at fair value (2)		71,284		13,483		—		—			84,767
Short-term investments, at fair value (1) (3)		—		450,681		—		—			450,681
Total investments available for sale	$	71,284	$	26,782,672	$	823,597	$	—		$	27,677,553
Cash equivalents (4)		1,358,619		540,646		—		—			1,899,265
Other investments (5)		—		432,166		133,717		—			565,883
Other assets (6)(7)		—		108,056		7,882		(22,995	)		92,943
Total assets accounted for at fair value	$	1,429,903	$	27,863,540	$	965,196	$	(22,995	)	$	30,235,644
Liabilities
Financial instruments sold, but not yet purchased (8)	$	256	$	21,270	$	—	$	—		$	21,526
Other liabilities (6)(7)		—		13,591		47,077		—			60,668
Total liabilities accounted for at fair value	$	256	$	34,861	$	47,077	$	—		$	82,194

Fair Value, Assets And Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Text Block]

	Level 3 Assets and Liabilities Year Ended December 31, 2011
(U.S. dollars in thousands)	Corporate			Residential mortgage-backed securities – Agency			Residential mortgage-backed securities – Non Agency			Commercial mortgage-backed securities			Collateralized debt obligations
Balance, beginning of period	$	36,866		$	30,255		$	4,964		$	1,623		$	721,572
Realized gains (losses)		(276	)		(11	)		—			—			(3,458	)
Movement in unrealized gains (losses)		92			(145	)		—			—			2,404
Purchases and issuances		14,840			6,176			—			—			2,379
Sales and settlements		(10,049	)		(4,186	)		—			—			(68,165	)
Transfers into Level 3		2,105			2,655			—			—			1,886
Transfers out of Level 3		(19,760	)		(2,703	)		(4,964	)		(1,623	)		(5,767	)
Fixed maturities to short-term investments classification change		—			—			—			—			—
Balance, end of period	$	23,818		$	32,041		$	—		$	—		$	650,851
Movement in total gains (losses) above relating to instruments still held at the reporting date	$	92		$	(156	)	$	—		$	—		$	(6,431	)

	Level 3 Assets and Liabilities Year Ended December 31, 2011 (Continued)
(U.S. dollars in thousands)	Other asset backed securities			Non-U.S. Sovereign Government and Supranationals and Government- Related			Short-term Investments		Other investments			Derivative Contracts - Net
Balance, beginning of period	$	24,650		$	3,667		$	—	$	133,717		$	(39,195	)
Realized gains (losses)		(849	)		—			—		11,592			—
Movement in unrealized gains (losses)		6,896			—			—		14,108			(3,173	)
Purchases and issuances		—			—			—		12,177			—
Sales and settlements		(9,114	)		—			—		(57,635	)		(276	)
Transfers into Level 3		—			—			—		—			—
Transfers out of Level 3		(5,031	)		(3,667	)		—		—			—
Fixed maturities to short-term investments classification change		—			—			—		—			—
Balance, end of period	$	16,552		$	—		$	—	$	113,959		$	(42,644	)
Movement in total gains (losses) above relating to instruments still held at the reporting date	$	12,334		$	—		$	—	$	23,391		$	(3,173	)

	Level 3 Assets and Liabilities Year Ended December 31, 2010
(U.S. dollars in thousands)	Corporate			Residential mortgage-backed securities – Agency			Residential mortgage-backed securities – Non Agency			Commercial mortgage-backed securities			Collateralized debt obligations
Balance, beginning of period	$	10,311		$	7,894		$	42,190		$	2,755		$	197,149
Realized gains (losses)		(7,257	)		(360	)		(1,452	)		(908	)		(28,253	)
Movement in unrealized gains (losses)		1,748			(74	)		306			1,062			120,932
Purchases and issuances		20,328			30,689			—			—			—
Sales and settlements		(2,164	)		—			(2,226	)		(685	)		(7,525	)
Transfers into Level 3		14,749			—			5,601			—			471,211
Transfers out of Level 3		(849	)		(7,894	)		(39,455	)		—			(59	)
Fixed maturities to short-term investments classification change		—			—			—			(601	)		(31,883	)
Balance, end of period	$	36,866		$	30,255		$	4,964		$	1,623		$	721,572
Movement in total gains (losses) above relating to instruments still held at the reporting date	$	1,964		$	(74	)	$	(28	)	$	223		$	117,764

	Level 3 Assets and Liabilities Year Ended December 31, 2010 (Continued)
(U.S. dollars in thousands)	Other asset backed securities			Non-U.S. Sovereign Government and Supranationals and Government- Related		Short-term Investments		Other investments			Derivative Contracts - Net
Balance, beginning of period	$	38,179		$	3,217	$	—	$	75,584		$	100,515
Realized gains (losses)		(18,107	)		—		—		3,677			874
Movement in unrealized gains (losses)		14,685			34		—		14,461			57,688
Purchases and issuances		4,356			—		—		15,443			(198,272	)
Sales and settlements		(1,504	)		—		—		(26,180	)		—
Transfers into Level 3		1,355			416		—		18,248			—
Transfers out of Level 3		(14,314	)		—		—		—			—
Fixed maturities to short-term investments classification change		—			—		—		32,484			—
Balance, end of period	$	24,650		$	3,667	$	—	$	133,717		$	(39,195	)
Movement in total gains (losses) above relating to instruments still held at the reporting date	$	8,747		$	34	$	—	$	14,286		$	57,688

Schedule Of Financial Instruments Not Carried at Fair Value [Text Block]

	2011				2010
(U.S. dollars in thousands)	Carrying Value		Fair Value		Carrying Value		Fair Value
Fixed maturities, held to maturity	$	2,668,978	$	2,895,668	$	2,728,335	$	2,742,626
Other investments – structured transactions		323,705		297,124		327,686		317,524
Financial Assets	$	2,992,683	$	3,192,792	$	3,056,021	$	3,060,150
Deposit Liabilities	$	1,608,108	$	1,809,812	$	1,684,606	$	1,737,107
Notes payable and debt		2,275,327		2,340,148		2,457,003		2,439,328
Financial Liabilities	$	3,883,435	$	4,149,960	$	4,141,609	$	4,176,435
Redeemable series C preference ordinary shares	$	—	$	—	$	71,900	$	61,115