v2.4.0.8
FAIR VALUE MEASUREMENTS (DETAILS) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2013
Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities $ 11,644,912 $ 11,928,049
Equity securities 618,795 666,548
Other investments 962,315 843,437
Short-term investments 45,904 108,860
Derivative assets (see Note 5) 7,792 5,838
Derivative liabilities (see Note 5) 9,722 3,737
Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 11,644,912 11,928,049
Equity securities 618,795 666,548
Other investments 962,315 843,437
Short-term investments 45,904 108,860
Derivative assets (see Note 5) 7,792 5,838
Total assets 13,279,718 13,552,732
Derivative liabilities (see Note 5) 9,722 3,737
Cash settled awards (see Note 7) 4,106 0
Total liabilities 13,828 3,737
US Government and Agency [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 1,338,814 1,422,885
US Government and Agency [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 1,338,814 1,422,885
Non-US Government [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 1,176,949 1,104,576
Non-US Government [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 1,176,949 1,104,576
Corporate Debt [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 3,479,916 3,876,382
Corporate Debt [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 3,479,916 3,876,382
Agency RMBS [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 2,333,624 2,659,908
Agency RMBS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 2,333,624 2,659,908
CMBS [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 774,650 840,084
CMBS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 774,650 840,084
Non-Agency RMBS [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 88,866 95,199
Non-Agency RMBS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 88,866 95,199
ABS [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 911,681 643,206
ABS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 911,681 643,206
Municipals [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 1,540,412 1,285,809
Municipals [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 1,540,412 1,285,809
Common Stock [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 390,180 443,398
Common Stock [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 390,180 443,398
Exchange-Traded Funds [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 119,236 119,161
Exchange-Traded Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 119,236 119,161
Non-U.S. Bond Mutual Funds [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 109,379 103,989
Non-U.S. Bond Mutual Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 109,379 103,989
Hedge Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Other investments 905,039 781,002
Direct Lending Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Other investments 4,232 0
CLO-Equities [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Other investments 53,044 62,435
Level 1 [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 1,168,380 1,094,220
Equity securities 509,416 562,559
Other investments 0 0
Short-term investments 0 0
Derivative assets (see Note 5) 0 0
Total assets 1,677,796 1,656,779
Derivative liabilities (see Note 5) 0 0
Cash settled awards (see Note 7) 0 0
Total liabilities 0 0
Level 1 [Member] | US Government and Agency [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 1,168,380 1,094,220
Level 1 [Member] | Non-US Government [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 0
Level 1 [Member] | Corporate Debt [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 0
Level 1 [Member] | Agency RMBS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 0
Level 1 [Member] | CMBS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 0
Level 1 [Member] | Non-Agency RMBS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 0
Level 1 [Member] | ABS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 0
Level 1 [Member] | Municipals [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 0
Level 1 [Member] | Common Stock [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 390,180 443,398
Level 1 [Member] | Exchange-Traded Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 119,236 119,161
Level 1 [Member] | Non-U.S. Bond Mutual Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 0 0
Level 1 [Member] | Hedge Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Other investments 0 0
Level 1 [Member] | Direct Lending Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Other investments 0 0
Level 1 [Member] | CLO-Equities [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Other investments 0 0
Level 2 [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 10,410,622 10,762,898
Equity securities 109,379 103,989
Other investments 460,819 421,006
Short-term investments 45,904 108,860
Derivative assets (see Note 5) 7,792 5,838
Total assets 11,034,516 11,402,591
Derivative liabilities (see Note 5) 9,722 3,737
Cash settled awards (see Note 7) 4,106 0
Total liabilities 13,828 3,737
Level 2 [Member] | US Government and Agency [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 170,434 328,665
Level 2 [Member] | Non-US Government [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 1,176,949 1,104,576
Level 2 [Member] | Corporate Debt [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 3,479,916 3,874,832
Level 2 [Member] | Agency RMBS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 2,333,624 2,659,908
Level 2 [Member] | CMBS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 762,865 835,788
Level 2 [Member] | Non-Agency RMBS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 88,866 94,089
Level 2 [Member] | ABS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 857,556 579,231
Level 2 [Member] | Municipals [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 1,540,412 1,285,809
Level 2 [Member] | Common Stock [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 0 0
Level 2 [Member] | Exchange-Traded Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 0 0
Level 2 [Member] | Non-U.S. Bond Mutual Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 109,379 103,989
Level 2 [Member] | Hedge Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Other investments 460,819 421,006
Level 2 [Member] | Direct Lending Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Other investments 0 0
Level 2 [Member] | CLO-Equities [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Other investments 0 0
Level 3 [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 65,910 70,931
Equity securities 0 0
Other investments 501,496 422,431
Short-term investments 0 0
Derivative assets (see Note 5) 0 0
Total assets 567,406 493,362
Derivative liabilities (see Note 5) 0 0
Cash settled awards (see Note 7) 0 0
Total liabilities 0 0
Level 3 [Member] | US Government and Agency [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 0
Level 3 [Member] | Non-US Government [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 0
Level 3 [Member] | Corporate Debt [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 1,550
Level 3 [Member] | Agency RMBS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 0
Level 3 [Member] | CMBS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 11,785 4,296
Level 3 [Member] | Non-Agency RMBS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 1,110
Level 3 [Member] | ABS [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 54,125 63,975
Level 3 [Member] | Municipals [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fixed maturities 0 0
Level 3 [Member] | Common Stock [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 0 0
Level 3 [Member] | Exchange-Traded Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 0 0
Level 3 [Member] | Non-U.S. Bond Mutual Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Equity securities 0 0
Level 3 [Member] | Hedge Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Other investments 444,220 359,996
Level 3 [Member] | Direct Lending Funds [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Other investments 4,232 0
Level 3 [Member] | CLO-Equities [Member] | Fair Value Measurements Recurring [Member]
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Other investments $ 53,044 $ 62,435