Fair Value (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	$ 13,593,303	$ 14,395,315
Short-term investments, trading securities, at fair value	13,546	150,552
Equities, trading securities	1,221,053	1,094,002
Other invested assets	135,139	71,204
Funds held - directly managed	561,306	833,247
Total	15,524,347	16,544,320
Short-term investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed	2,426
Derivative assets [Member] | Foreign exchange forward contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	1,249	7,889
Derivative assets [Member] | Foreign currency option contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		1,410
Derivative assets [Member] | Futures contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	41,031	1,956
Derivative assets [Member] | Credit default swaps (protection purchased) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		6
Derivative assets [Member] | Credit default swaps (assumed risks) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		512
Derivative assets [Member] | Total return swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	79	6,630
Derivative assets [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	2,147
Derivative assets [Member] | TBAs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	2	115
Derivative liabilities [Member] | Foreign exchange forward contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(8,648)	(17,395)
Derivative liabilities [Member] | Foreign currency option contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(535)	(186)
Derivative liabilities [Member] | Futures contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		(1,352)
Derivative liabilities [Member] | Credit default swaps (protection purchased) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(71)	(807)
Derivative liabilities [Member] | Insurance-linked securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(268)	(2,173)
Derivative liabilities [Member] | Total return swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(599)	(546)
Derivative liabilities [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(2,558)	(7,880)
Derivative liabilities [Member] | TBAs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(1,331)	(163)
Notes And Loan Receivables And Notes Securitization [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	41,446	34,902
Annuities and residuals [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	24,064	46,882
Private Equities Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	39,131	1,404
Other invested assets funds held directly managed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed	15,165	17,976
Real estate investment trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	175,796	66,846
Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	159,509	118,213
Insurance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	144,020	39,132
Finance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	138,707	100,405
Consumer noncyclical [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	108,663	130,526
Communications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	72,991	65,722
Technology [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	61,520	78,914
Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	47,677	59,242
Consumer cyclical [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	45,915	62,526
Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	37,151
Other equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	19,993	60,913
Mutual funds and exchange traded funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	209,111	311,563
US Government and government sponsored enterpises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	1,623,859	1,130,924
Funds held - directly managed	157,296	218,696
US states, territories and municipalities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	124,587	243,386
Funds held - directly managed	286	345
Non US sovereign government supranational and government related [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	2,353,699	2,375,673
Funds held - directly managed	137,186	233,987
Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	6,048,663	6,655,838
Funds held - directly managed	248,947	362,243
Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	1,138,231	723,470
Residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	2,268,517	3,199,924
Other mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	35,747	66,100
Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	0	0
Short-term investments, trading securities, at fair value	0	0
Equities, trading securities	1,034,130	788,556
Other invested assets	41,031	604
Funds held - directly managed	0	0
Total	1,075,161	789,160
Quoted prices in active markets for identical assets (Level 1) | Short-term investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed	0
Quoted prices in active markets for identical assets (Level 1) | Derivative assets [Member] | Foreign exchange forward contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Derivative assets [Member] | Foreign currency option contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		0
Quoted prices in active markets for identical assets (Level 1) | Derivative assets [Member] | Futures contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	41,031	1,956
Quoted prices in active markets for identical assets (Level 1) | Derivative assets [Member] | Credit default swaps (protection purchased) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		0
Quoted prices in active markets for identical assets (Level 1) | Derivative assets [Member] | Credit default swaps (assumed risks) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		0
Quoted prices in active markets for identical assets (Level 1) | Derivative assets [Member] | Total return swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Derivative assets [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0
Quoted prices in active markets for identical assets (Level 1) | Derivative assets [Member] | TBAs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Derivative liabilities [Member] | Foreign exchange forward contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Derivative liabilities [Member] | Foreign currency option contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Derivative liabilities [Member] | Futures contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		(1,352)
Quoted prices in active markets for identical assets (Level 1) | Derivative liabilities [Member] | Credit default swaps (protection purchased) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Derivative liabilities [Member] | Insurance-linked securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Derivative liabilities [Member] | Total return swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Derivative liabilities [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Derivative liabilities [Member] | TBAs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Notes And Loan Receivables And Notes Securitization [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Annuities and residuals [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Private Equities Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Quoted prices in active markets for identical assets (Level 1) | Other invested assets funds held directly managed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed	0	0
Quoted prices in active markets for identical assets (Level 1) | Real estate investment trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	175,796	66,846
Quoted prices in active markets for identical assets (Level 1) | Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	159,509	118,213
Quoted prices in active markets for identical assets (Level 1) | Insurance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	144,020	39,132
Quoted prices in active markets for identical assets (Level 1) | Finance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	108,944	79,456
Quoted prices in active markets for identical assets (Level 1) | Consumer noncyclical [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	108,663	130,526
Quoted prices in active markets for identical assets (Level 1) | Communications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	70,792	65,722
Quoted prices in active markets for identical assets (Level 1) | Technology [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	53,768	71,927
Quoted prices in active markets for identical assets (Level 1) | Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	47,677	59,242
Quoted prices in active markets for identical assets (Level 1) | Consumer cyclical [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	45,915	62,526
Quoted prices in active markets for identical assets (Level 1) | Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	37,151
Quoted prices in active markets for identical assets (Level 1) | Other equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	19,993	60,913
Quoted prices in active markets for identical assets (Level 1) | Mutual funds and exchange traded funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	61,902	34,053
Quoted prices in active markets for identical assets (Level 1) | US Government and government sponsored enterpises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	0	0
Funds held - directly managed	0	0
Quoted prices in active markets for identical assets (Level 1) | US states, territories and municipalities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	0	0
Funds held - directly managed	0	0
Quoted prices in active markets for identical assets (Level 1) | Non US sovereign government supranational and government related [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	0	0
Funds held - directly managed	0	0
Quoted prices in active markets for identical assets (Level 1) | Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	0	0
Funds held - directly managed	0	0
Quoted prices in active markets for identical assets (Level 1) | Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	0	0
Quoted prices in active markets for identical assets (Level 1) | Residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	0	0
Quoted prices in active markets for identical assets (Level 1) | Other mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	0	0
Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	13,038,346	13,738,042
Short-term investments, trading securities, at fair value	13,546	150,552
Equities, trading securities	148,878	277,718
Other invested assets	(9,745)	(16,499)
Funds held - directly managed	545,855	814,926
Total	13,736,880	14,964,739
Significant other observable inputs (Level 2) | Short-term investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed	2,426
Significant other observable inputs (Level 2) | Derivative assets [Member] | Foreign exchange forward contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	1,249	7,889
Significant other observable inputs (Level 2) | Derivative assets [Member] | Foreign currency option contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		1,410
Significant other observable inputs (Level 2) | Derivative assets [Member] | Futures contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant other observable inputs (Level 2) | Derivative assets [Member] | Credit default swaps (protection purchased) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		6
Significant other observable inputs (Level 2) | Derivative assets [Member] | Credit default swaps (assumed risks) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		512
Significant other observable inputs (Level 2) | Derivative assets [Member] | Total return swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant other observable inputs (Level 2) | Derivative assets [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	2,147
Significant other observable inputs (Level 2) | Derivative assets [Member] | TBAs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	2	115
Significant other observable inputs (Level 2) | Derivative liabilities [Member] | Foreign exchange forward contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(8,648)	(17,395)
Significant other observable inputs (Level 2) | Derivative liabilities [Member] | Foreign currency option contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(535)	(186)
Significant other observable inputs (Level 2) | Derivative liabilities [Member] | Futures contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		0
Significant other observable inputs (Level 2) | Derivative liabilities [Member] | Credit default swaps (protection purchased) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(71)	(807)
Significant other observable inputs (Level 2) | Derivative liabilities [Member] | Insurance-linked securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant other observable inputs (Level 2) | Derivative liabilities [Member] | Total return swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant other observable inputs (Level 2) | Derivative liabilities [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(2,558)	(7,880)
Significant other observable inputs (Level 2) | Derivative liabilities [Member] | TBAs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(1,331)	(163)
Significant other observable inputs (Level 2) | Notes And Loan Receivables And Notes Securitization [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant other observable inputs (Level 2) | Annuities and residuals [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant other observable inputs (Level 2) | Private Equities Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant other observable inputs (Level 2) | Other invested assets funds held directly managed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed	0	0
Significant other observable inputs (Level 2) | Real estate investment trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant other observable inputs (Level 2) | Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant other observable inputs (Level 2) | Insurance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant other observable inputs (Level 2) | Finance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	9,556	7,472
Significant other observable inputs (Level 2) | Consumer noncyclical [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant other observable inputs (Level 2) | Communications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant other observable inputs (Level 2) | Technology [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant other observable inputs (Level 2) | Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant other observable inputs (Level 2) | Consumer cyclical [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant other observable inputs (Level 2) | Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0
Significant other observable inputs (Level 2) | Other equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant other observable inputs (Level 2) | Mutual funds and exchange traded funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	139,322	270,246
Significant other observable inputs (Level 2) | US Government and government sponsored enterpises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	1,623,859	1,130,924
Funds held - directly managed	157,296	218,696
Significant other observable inputs (Level 2) | US states, territories and municipalities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	16,207	10,151
Funds held - directly managed	0	0
Significant other observable inputs (Level 2) | Non US sovereign government supranational and government related [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	2,353,699	2,375,673
Funds held - directly managed	137,186	233,987
Significant other observable inputs (Level 2) | Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	6,048,663	6,554,934
Funds held - directly managed	248,947	362,243
Significant other observable inputs (Level 2) | Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	691,654	400,336
Significant other observable inputs (Level 2) | Residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	2,268,517	3,199,924
Significant other observable inputs (Level 2) | Other mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	35,747	66,100
Significant unobservable inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	554,957	657,273
Short-term investments, trading securities, at fair value	0	0
Equities, trading securities	38,045	27,728
Other invested assets	103,853	87,099
Funds held - directly managed	15,451	18,321
Total	712,306	790,421
Significant unobservable inputs (Level 3) [Member] | Short-term investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed	0
Significant unobservable inputs (Level 3) [Member] | Derivative assets [Member] | Foreign exchange forward contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant unobservable inputs (Level 3) [Member] | Derivative assets [Member] | Foreign currency option contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		0
Significant unobservable inputs (Level 3) [Member] | Derivative assets [Member] | Futures contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant unobservable inputs (Level 3) [Member] | Derivative assets [Member] | Credit default swaps (protection purchased) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		0
Significant unobservable inputs (Level 3) [Member] | Derivative assets [Member] | Credit default swaps (assumed risks) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		0
Significant unobservable inputs (Level 3) [Member] | Derivative assets [Member] | Total return swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	79	6,630
Significant unobservable inputs (Level 3) [Member] | Derivative assets [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0
Significant unobservable inputs (Level 3) [Member] | Derivative assets [Member] | TBAs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant unobservable inputs (Level 3) [Member] | Derivative liabilities [Member] | Foreign exchange forward contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant unobservable inputs (Level 3) [Member] | Derivative liabilities [Member] | Foreign currency option contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant unobservable inputs (Level 3) [Member] | Derivative liabilities [Member] | Futures contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		0
Significant unobservable inputs (Level 3) [Member] | Derivative liabilities [Member] | Credit default swaps (protection purchased) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant unobservable inputs (Level 3) [Member] | Derivative liabilities [Member] | Insurance-linked securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(268)	(2,173)
Significant unobservable inputs (Level 3) [Member] | Derivative liabilities [Member] | Total return swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(599)	(546)
Significant unobservable inputs (Level 3) [Member] | Derivative liabilities [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant unobservable inputs (Level 3) [Member] | Derivative liabilities [Member] | TBAs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0	0
Significant unobservable inputs (Level 3) [Member] | Notes And Loan Receivables And Notes Securitization [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	41,446	34,902
Significant unobservable inputs (Level 3) [Member] | Annuities and residuals [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	24,064	46,882
Significant unobservable inputs (Level 3) [Member] | Private Equities Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	39,131	1,404
Significant unobservable inputs (Level 3) [Member] | Other invested assets funds held directly managed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed	15,165	17,976
Significant unobservable inputs (Level 3) [Member] | Real estate investment trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant unobservable inputs (Level 3) [Member] | Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant unobservable inputs (Level 3) [Member] | Insurance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant unobservable inputs (Level 3) [Member] | Finance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	20,207	13,477
Significant unobservable inputs (Level 3) [Member] | Consumer noncyclical [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant unobservable inputs (Level 3) [Member] | Communications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	2,199	0
Significant unobservable inputs (Level 3) [Member] | Technology [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	7,752	6,987
Significant unobservable inputs (Level 3) [Member] | Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant unobservable inputs (Level 3) [Member] | Consumer cyclical [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant unobservable inputs (Level 3) [Member] | Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0
Significant unobservable inputs (Level 3) [Member] | Other equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	0	0
Significant unobservable inputs (Level 3) [Member] | Mutual funds and exchange traded funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	7,887	7,264
Significant unobservable inputs (Level 3) [Member] | US Government and government sponsored enterpises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	0	0
Funds held - directly managed	0	0
Significant unobservable inputs (Level 3) [Member] | US states, territories and municipalities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	108,380	233,235
Funds held - directly managed	286	345
Significant unobservable inputs (Level 3) [Member] | Non US sovereign government supranational and government related [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	0	0
Funds held - directly managed	0	0
Significant unobservable inputs (Level 3) [Member] | Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	0	100,904
Funds held - directly managed	0	0
Significant unobservable inputs (Level 3) [Member] | Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	446,577	323,134
Significant unobservable inputs (Level 3) [Member] | Residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	0	0
Significant unobservable inputs (Level 3) [Member] | Other mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	$ 0	$ 0