v2.4.0.6

Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Total fixed maturity investments	$ 4,302,119		$ 4,433,517
Short-term investments	1,172,839		905,477
Equity investments trading	53,080		50,560
Other investments	806,782		748,984
Total other assets and (liabilities)	53,504		16,071
Total assets and liabilities measured on recurring basis	6,388,324		6,154,609
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	1,309,243		885,152
Short-term investments	0		0
Equity investments trading	53,080		50,560
Other investments	0		0
Total other assets and (liabilities)	(1,068)		(6,162)
Total assets and liabilities measured on recurring basis	1,361,255		929,550
Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	2,965,038		3,520,604
Short-term investments	1,172,839		905,477
Equity investments trading	0		0
Other investments	388,245		352,458
Total other assets and (liabilities)	6,427		(6,293)
Total assets and liabilities measured on recurring basis	4,532,549		4,772,246
Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	27,838		27,761
Short-term investments	0		0
Equity investments trading	0		0
Other investments	418,537		396,526
Total other assets and (liabilities)	48,145		28,526
Total assets and liabilities measured on recurring basis	494,520		452,813
U.S. treasuries [Member]
Total fixed maturity investments	1,309,243		885,152
U.S. treasuries [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	1,309,243		885,152
U.S. treasuries [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	0		0
U.S. treasuries [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	0		0
Agencies [Member]
Total fixed maturity investments	343,575		158,561
Agencies [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	0		0
Agencies [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	343,575		158,561
Agencies [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	0		0
Non-U.S. government (Sovereign Debt) [Member]
Total fixed maturity investments	130,899		227,912
Non-U.S. government (Sovereign Debt) [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	0		0
Non-U.S. government (Sovereign Debt) [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	130,899		227,912
Non-U.S. government (Sovereign Debt) [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	0		0
FDIC guaranteed corporate [Member]
Total fixed maturity investments	103,554		423,630
FDIC guaranteed corporate [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	0		0
FDIC guaranteed corporate [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	103,554		423,630
FDIC guaranteed corporate [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	0		0
Non-U.S. government-backed corporate [Member]
Total fixed maturity investments	501,160		641,082
Non-U.S. government-backed corporate [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	0		0
Non-U.S. government-backed corporate [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	501,160		641,082
Non-U.S. government-backed corporate [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	0		0
Corporate [Member]
Total fixed maturity investments	1,146,211		1,206,904
Corporate [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	0		0
Corporate [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	1,118,373		1,179,143
Corporate [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	27,838		27,761
Agency mortgage-backed [Member]
Total fixed maturity investments	319,215		441,749
Agency mortgage-backed [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	0		0
Agency mortgage-backed [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	319,215		441,749
Agency mortgage-backed [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	0		0
Non-agency mortgage-backed [Member]
Total fixed maturity investments	108,047		104,771
Non-agency mortgage-backed [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	0		0
Non-agency mortgage-backed [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	108,047		104,771
Non-agency mortgage-backed [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	0		0
Commercial mortgage-backed [Member]
Total fixed maturity investments	329,343		325,729
Commercial mortgage-backed [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	0		0
Commercial mortgage-backed [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	329,343		325,729
Commercial mortgage-backed [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	0		0
Asset-backed [Member]
Total fixed maturity investments	10,872		18,027
Asset-backed [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total fixed maturity investments	0		0
Asset-backed [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total fixed maturity investments	10,872		18,027
Asset-backed [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total fixed maturity investments	0		0
Private equity partnerships [Member]
Other investments	389,451		367,909
Private equity partnerships [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Other investments	0		0
Private equity partnerships [Member] | Significant Other Observable Inputs (Level 2) [Member]
Other investments	0		0
Private equity partnerships [Member] | Significant Unobservable Inputs (Level 3) [Member]
Other investments	389,451		367,909
Senior secured bank loan funds [Member]
Other investments	266,141		257,870
Senior secured bank loan funds [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Other investments	0		0
Senior secured bank loan funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Other investments	245,141		237,815
Senior secured bank loan funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Other investments	21,000		20,055
Catastrophe bonds [Member]
Other investments	95,827		70,999
Catastrophe bonds [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Other investments	0		0
Catastrophe bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Other investments	95,827		70,999
Catastrophe bonds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Other investments	0		0
Non-U.S. fixed income funds [Member]
Other investments	31,713		28,862
Non-U.S. fixed income funds [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Other investments	0		0
Non-U.S. fixed income funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Other investments	31,713		28,862
Non-U.S. fixed income funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Other investments	0		0
Hedge Funds [Member]
Other investments	22,310		21,344
Hedge Funds [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Other investments	0		0
Hedge Funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Other investments	15,564		14,782
Hedge Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Other investments	6,746		6,562
Miscellaneous other investments [Member]
Other investments	1,340		2,000
Miscellaneous other investments [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Other investments	0		0
Miscellaneous other investments [Member] | Significant Other Observable Inputs (Level 2) [Member]
Other investments	0		0
Miscellaneous other investments [Member] | Significant Unobservable Inputs (Level 3) [Member]
Other investments	1,340		2,000
Assumed and ceded reinsurance contracts [Member]
Total other assets and (liabilities)	6,163		2,115
Assumed and ceded reinsurance contracts [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total other assets and (liabilities)	0		0
Assumed and ceded reinsurance contracts [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total other assets and (liabilities)	0		0
Assumed and ceded reinsurance contracts [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total other assets and (liabilities)	6,163		2,115
Derivatives [Member]
Total other assets and (liabilities)	33,405	[1]	3,312	[1]
Derivatives [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total other assets and (liabilities)	413		707	[1]
Derivatives [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total other assets and (liabilities)	6,427		(6,293)	[1]
Derivatives [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total other assets and (liabilities)	26,565		8,898	[1]
Other [Member]
Total other assets and (liabilities)	13,936		10,644
Other [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Total other assets and (liabilities)	(1,481)		(6,869)
Other [Member] | Significant Other Observable Inputs (Level 2) [Member]
Total other assets and (liabilities)	0		0
Other [Member] | Significant Unobservable Inputs (Level 3) [Member]
Total other assets and (liabilities)	$ 15,417		$ 17,513
[1] See "Note 11. Derivative Instruments" for additional information related to the fair value by type of contract, of derivatives entered into by the Company.

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