Fair Value (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	$ 13,898,401	$ 13,593,303
Short-term investments, trading securities, at fair value	28,821	13,546
Equities, trading securities	1,249,744	1,221,053
Other invested assets	113,339	135,139
Funds held - directly managed	596,333	561,306
Total	15,886,638	15,524,347
Short-term investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Funds held - directly managed	3,477	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	4,404	1,249
Derivative assets [Member] | Foreign currency option contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	398
Derivative assets [Member] | Futures contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	18,814	41,031
Derivative assets [Member] | Total return swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	181	79
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
Derivative liabilities [Member] | Foreign exchange forward contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(5,888)	(8,648)
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)
Derivative liabilities [Member] | Futures contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(5)
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)
Derivative liabilities [Member] | Insurance-linked securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(740)	(268)
Derivative liabilities [Member] | Total return swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(483)	(599)
Derivative liabilities [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(5,797)	(2,558)
Derivative liabilities [Member] | TBAs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	(1,388)	(1,331)
Notes And Loan Receivables And Notes Securitization [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	42,243	41,446
Annuities and residuals [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	18,945	24,064
Private Equities Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	42,655	39,131
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	15,223	15,165
Real estate investment trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	196,661	175,796
Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	160,093	159,509
Insurance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	136,040	144,020
Finance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	130,138	138,707
Consumer noncyclical [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	112,721	108,663
Communications [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	85,835	72,991
Technology [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	62,663	61,520
Industrials [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	47,622	47,677
Consumer cyclical [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	45,709	45,915
Utilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	38,605	37,151
Other equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	20,929	19,993
Mutual funds and exchange traded funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	212,728	209,111
US Government and government sponsored enterpises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	1,866,135	1,623,859
Funds held - directly managed	153,426	157,296
US states, territories and municipalities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	129,905	124,587
Funds held - directly managed	301	286
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	2,332,066	2,353,699
Funds held - directly managed	178,839	137,186
Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	5,989,320	6,048,663
Funds held - directly managed	245,067	248,947
Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	1,151,451	1,138,231
Residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	2,384,629	2,268,517
Other mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	44,895	35,747
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	1,020,400	1,034,130
Other invested assets	18,809	41,031
Funds held - directly managed	0	0
Total	1,039,209	1,075,161
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	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	18,814	41,031
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
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
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	(5)
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
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	196,661	175,796
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	160,093	159,509
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	136,040	144,020
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	97,863	108,944
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	112,721	108,663
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	83,724	70,792
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	55,263	53,768
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	47,622	47,677
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	45,709	45,915
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	38,605	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	20,929	19,993
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	25,170	61,902
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	13,337,233	13,038,346
Short-term investments, trading securities, at fair value	28,821	13,546
Equities, trading securities	189,074	148,878
Other invested assets	(8,271)	(9,745)
Funds held - directly managed	580,809	545,855
Total	14,127,666	13,736,880
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	3,477	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	4,404	1,249
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	398
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] | 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
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	(5,888)	(8,648)
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)
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)
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	(5,797)	(2,558)
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	(1,388)	(1,331)
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	9,569	9,556
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	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	179,505	139,322
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	1,866,135	1,623,859
Funds held - directly managed	153,426	157,296
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	16,438	16,207
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	2,332,066	2,353,699
Funds held - directly managed	178,839	137,186
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	5,989,320	6,048,663
Funds held - directly managed	245,067	248,947
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	703,750	691,654
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	2,384,629	2,268,517
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	44,895	35,747
Significant unobservable inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities, trading securities	561,168	554,957
Short-term investments, trading securities, at fair value	0	0
Equities, trading securities	40,270	38,045
Other invested assets	102,801	103,853
Funds held - directly managed	15,524	15,451
Total	719,763	712,306
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	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] | Total return swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	181	79
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
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
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
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	(740)	(268)
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	(483)	(599)
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	42,243	41,446
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	18,945	24,064
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	42,655	39,131
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	15,223	15,165
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	22,706	20,207
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	2,111	2,199
Significant unobservable inputs (Level 3) [Member] | Technology [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equities, trading securities	7,400	7,752
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	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	8,053	7,887
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	113,467	108,380
Funds held - directly managed	301	286
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	0
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	447,701	446,577
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