v2.3.0.15

Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Total fixed maturity investments	$ 3,837,638	$ 4,116,697
Short-term investments	1,557,937	1,110,364
Equity investments trading	45,607
Other investments	736,757	787,548
Other secured assets		14,250
Total other assets and (liabilities)	20,513	63,019
Total assets and liabilities measured on recurring basis	6,198,452	6,091,878
U.S. Treasuries [Member]
Total fixed maturity investments	428,865	761,461
U.S. Treasuries [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	428,865	761,461
Agencies [Member]
Total fixed maturity investments	127,063	216,963
Agencies [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	127,063	216,963
Non-U.S. Government (Sovereign Debt) [Member]
Total fixed maturity investments	402,288	184,387
Non-U.S. Government (Sovereign Debt) [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	402,288	184,387
FDIC Guaranteed Corporate [Member]
Total fixed maturity investments	183,314	388,468
FDIC Guaranteed Corporate [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	183,314	388,468
Non-U.S. Government-Backed Corporate [Member]
Total fixed maturity investments	594,897	357,504
Non-U.S. Government-Backed Corporate [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	594,897	357,504
Corporate [Member]
Total fixed maturity investments	1,294,442	1,512,411
Corporate [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	1,273,528	1,490,626
Corporate [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	20,914	21,785
Agency Mortgage-Backed [Member]
Total fixed maturity investments	363,814	401,807
Agency Mortgage-Backed [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	363,814	401,807
Non-Agency Mortgage-Backed [Member]
Total fixed maturity investments	104,541	34,149
Non-Agency Mortgage-Backed [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	104,541	34,149
Commercial Mortgage-Backed [Member]
Total fixed maturity investments	318,805	219,440
Commercial Mortgage-Backed [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	318,805	219,440
Asset-Backed [Member]
Total fixed maturity investments	19,609	40,107
Asset-Backed [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	19,609	40,107
Private Equity Funds [Member]
Other investments	345,986	347,556
Private Equity Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Other investments	345,986	347,556
Senior Secured Bank Loan Funds [Member]
Other investments	243,766	166,106
Senior Secured Bank Loan Funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Other investments	231,251	158,386
Senior Secured Bank Loan Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Other investments	12,515	7,720
Catastrophe Bonds [Member]
Other investments	85,800	123,961
Catastrophe Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Other investments	85,619	123,961
Catastrophe Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Other investments	181
Non-U.S. Fixed Income Funds [Member]
Other investments	29,440	80,224
Non-U.S. Fixed Income Funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Other investments	29,440	80,224
Hedge Funds [Member]
Other investments	26,810	41,005
Hedge Funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Other investments	26,810	41,005
Miscellaneous Investments [Member]
Other investments	4,955	28,696
Miscellaneous Investments [Member] | Significant Other Observable Inputs (Level 2) [Member]
Other investments		21,870
Miscellaneous Investments [Member] | Significant Unobservable Inputs (Level 3) [Member]
Other investments	4,955	6,826
Platinum Warrants [Member]
Total other assets and (liabilities)		44,925
Platinum Warrants [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total other assets and (liabilities)		44,925
Assumed And Ceded (Re)Insurance Contracts [Member]
Total other assets and (liabilities)	4,418	1,772
Assumed And Ceded (Re)Insurance Contracts [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total other assets and (liabilities)	4,418	1,772
Derivatives Assets [Member]
Total other assets and (liabilities)	2,720	2,693
Derivatives Assets [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total other assets and (liabilities)	(773)	(51)
Derivatives Assets [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total other assets and (liabilities)	950	6,245
Derivatives Assets [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total other assets and (liabilities)	2,543	(3,501)
Other [Member]
Total other assets and (liabilities)	13,375	13,629
Other [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total other assets and (liabilities)	(4,241)	(4,599)
Other [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total other assets and (liabilities)	17,616	18,228
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	428,865	761,461
Equity investments trading	45,607
Total other assets and (liabilities)	(5,014)	(4,650)
Total assets and liabilities measured on recurring basis	469,458	756,811
Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	3,387,859	3,333,451
Short-term investments	1,557,937	1,110,364
Other investments	373,120	425,446
Other secured assets		14,250
Total other assets and (liabilities)	950	51,170
Total assets and liabilities measured on recurring basis	5,319,866	4,934,681
Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	20,914	21,785
Other investments	363,637	362,102
Total other assets and (liabilities)	24,577	16,499
Total assets and liabilities measured on recurring basis	$ 409,128	$ 400,386

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