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FAIR VALUE MEASUREMENTS (Financial Instruments Measured at Fair Value) (Details) - USD ($) $ in Thousands | Jun. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | $ 12,522,955 | $ 11,435,347
Equity securities | 433,407 | 381,633
Other investments, at fair value | 802,064 | 787,787
Short-term investments | 32,421 | 144,040
Derivative instruments (refer to Note 5) | 863 | 8,237
Total Assets | 13,791,710 | 12,757,044
Derivative instruments (refer to Note 5) | 12,948 | 14,522
Cash settled awards (refer to Note 8) | 12,946 | 20,648
Total Liabilities | 25,894 | 35,170
U.S. government and agency |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 2,317,427 | 1,515,697
Non-U.S. government |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 537,824 | 493,016
Corporate debt |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 4,945,585 | 4,876,921
Agency RMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 1,686,912 | 1,643,308
CMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 1,184,268 | 1,092,530
Non-Agency RMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 55,980 | 40,687
ABS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 1,600,771 | 1,637,603
Municipals |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 194,188 | 135,585
Common stocks |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 257 | 527
Exchange-traded funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 273,269 | 236,839
Bond mutual funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 159,881 | 144,267
Hedge funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 195,649 | 194,598
Direct lending funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 273,864 | 274,478
Private equity funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 60,285 | 64,566
Real estate funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 134,763 | 84,202
Other privately held investments |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 28,452 | 44,518
CLO-Equities |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 17,798 | 21,271
Overseas deposits |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 91,253 | 104,154
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 | 2,281,604 | 1,480,466
Equity securities | 273,526 | 237,366
Other investments, at fair value | 0 | 0
Short-term investments | 0 | 0
Derivative instruments (refer to Note 5) | 0 | 0
Total Assets | 2,555,130 | 1,717,832
Derivative instruments (refer to Note 5) | 0 | 0
Cash settled awards (refer to Note 8) | 0 | 0
Total Liabilities | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | U.S. government and agency |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 2,281,604 | 1,480,466
Quoted prices in active markets for identical assets (Level 1) | Non-U.S. government |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Corporate debt |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Agency RMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | CMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Non-Agency RMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | ABS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Municipals |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Common stocks |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 257 | 527
Quoted prices in active markets for identical assets (Level 1) | Exchange-traded funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 273,269 | 236,839
Quoted prices in active markets for identical assets (Level 1) | Bond mutual funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Hedge funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Direct lending funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Private equity funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Real estate funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Other privately held investments |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | CLO-Equities |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Overseas deposits |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Significant other observable inputs (Level 2) |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 10,191,831 | 9,868,202
Equity securities | 159,881 | 144,267
Other investments, at fair value | 91,253 | 104,154
Short-term investments | 32,421 | 144,040
Derivative instruments (refer to Note 5) | 863 | 8,237
Total Assets | 10,476,249 | 10,268,900
Derivative instruments (refer to Note 5) | 2,686 | 4,223
Cash settled awards (refer to Note 8) | 12,946 | 20,648
Total Liabilities | 15,632 | 24,871
Significant other observable inputs (Level 2) | U.S. government and agency |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 35,823 | 35,231
Significant other observable inputs (Level 2) | Non-U.S. government |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 537,824 | 493,016
Significant other observable inputs (Level 2) | Corporate debt |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 4,906,448 | 4,827,909
Significant other observable inputs (Level 2) | Agency RMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 1,686,912 | 1,643,308
Significant other observable inputs (Level 2) | CMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 1,174,376 | 1,073,396
Significant other observable inputs (Level 2) | Non-Agency RMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 55,980 | 40,687
Significant other observable inputs (Level 2) | ABS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 1,600,280 | 1,619,070
Significant other observable inputs (Level 2) | Municipals |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 194,188 | 135,585
Significant other observable inputs (Level 2) | Common stocks |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 0 | 0
Significant other observable inputs (Level 2) | Exchange-traded funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 0 | 0
Significant other observable inputs (Level 2) | Bond mutual funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 159,881 | 144,267
Significant other observable inputs (Level 2) | Hedge funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Significant other observable inputs (Level 2) | Direct lending funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Significant other observable inputs (Level 2) | Private equity funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Significant other observable inputs (Level 2) | Real estate funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Significant other observable inputs (Level 2) | Other privately held investments |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Significant other observable inputs (Level 2) | CLO-Equities |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Significant other observable inputs (Level 2) | Overseas deposits |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 91,253 | 104,154
Significant unobservable inputs (Level 3) |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 49,520 | 86,679
Equity securities | 0 | 0
Other investments, at fair value | 46,250 | 65,789
Short-term investments | 0 | 0
Derivative instruments (refer to Note 5) | 0 | 0
Total Assets | 95,770 | 152,468
Derivative instruments (refer to Note 5) | 10,262 | 10,299
Cash settled awards (refer to Note 8) | 0 | 0
Total Liabilities | 10,262 | 10,299
Significant unobservable inputs (Level 3) | U.S. government and agency |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 0 | 0
Significant unobservable inputs (Level 3) | Non-U.S. government |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 0 | 0
Significant unobservable inputs (Level 3) | Corporate debt |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 39,137 | 49,012
Significant unobservable inputs (Level 3) | Agency RMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 0 | 0
Significant unobservable inputs (Level 3) | CMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 9,892 | 19,134
Significant unobservable inputs (Level 3) | Non-Agency RMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 0 | 0
Significant unobservable inputs (Level 3) | ABS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 491 | 18,533
Significant unobservable inputs (Level 3) | Municipals |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 0 | 0
Significant unobservable inputs (Level 3) | Common stocks |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 0 | 0
Significant unobservable inputs (Level 3) | Exchange-traded funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 0 | 0
Significant unobservable inputs (Level 3) | Bond mutual funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 0 | 0
Significant unobservable inputs (Level 3) | Hedge funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Significant unobservable inputs (Level 3) | Direct lending funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Significant unobservable inputs (Level 3) | Private equity funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Significant unobservable inputs (Level 3) | Real estate funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Significant unobservable inputs (Level 3) | Other privately held investments |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 28,452 | 44,518
Significant unobservable inputs (Level 3) | CLO-Equities |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 17,798 | 21,271
Significant unobservable inputs (Level 3) | Overseas deposits |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Fair value based on NAV practical expedient |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 664,561 | 617,844
Fair value based on NAV practical expedient | Hedge funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 195,649 | 194,598
Fair value based on NAV practical expedient | Direct lending funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 273,864 | 274,478
Fair value based on NAV practical expedient | Private equity funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 60,285 | 64,566
Fair value based on NAV practical expedient | Real estate funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 134,763 | 84,202
Fair value based on NAV practical expedient | Other privately held investments |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Fair value based on NAV practical expedient | CLO-Equities |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 0 | 0
Fair value based on NAV practical expedient | Overseas deposits |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | $ 0 | $ 0

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