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FAIR VALUE MEASUREMENTS (Financial Instruments Measured at Fair Value) (Details) - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | $ 11,874,518 | $ 11,435,347
Equity securities | 418,863 | 381,633
Other investments, at fair value | 795,331 | 787,787
Short-term investments | 41,853 | 144,040
Derivative instruments (refer to Note 5) | 3,468 | 8,237
Total Assets | 13,134,033 | 12,757,044
Derivative instruments (refer to Note 5) | 13,837 | 14,522
Cash settled awards (refer to Note 8) | 7,878 | 20,648
Total Liabilities | 21,715 | 35,170
U.S. government and agency |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 1,973,654 | 1,515,697
Non-U.S. government |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 487,663 | 493,016
Corporate debt |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 4,838,265 | 4,876,921
Agency RMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 1,705,962 | 1,643,308
CMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 1,052,140 | 1,092,530
Non-Agency RMBS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 47,411 | 40,687
ABS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 1,613,010 | 1,637,603
Municipals |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 156,413 | 135,585
Common stocks |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 585 | 527
Exchange-traded funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 271,608 | 236,839
Bond mutual funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities | 146,670 | 144,267
Hedge funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 184,747 | 194,598
Direct lending funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 272,752 | 274,478
Private equity funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 61,526 | 64,566
Real estate funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 111,169 | 84,202
Other privately held investments |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 47,685 | 44,518
CLO-Equities |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 18,022 | 21,271
Overseas deposits |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Other investments, at fair value | 99,430 | 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 | 1,958,315 | 1,480,466
Equity securities | 272,193 | 237,366
Other investments, at fair value | 0 | 0
Short-term investments | 0 | 0
Derivative instruments (refer to Note 5) | 0 | 0
Total Assets | 2,230,508 | 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 | 1,958,315 | 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 | 585 | 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 | 271,608 | 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 | 9,851,890 | 9,868,202
Equity securities | 146,670 | 144,267
Other investments, at fair value | 99,430 | 104,154
Short-term investments | 41,853 | 144,040
Derivative instruments (refer to Note 5) | 3,468 | 8,237
Total Assets | 10,143,311 | 10,268,900
Derivative instruments (refer to Note 5) | 3,604 | 4,223
Cash settled awards (refer to Note 8) | 7,878 | 20,648
Total Liabilities | 11,482 | 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 | 15,339 | 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 | 487,663 | 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 | 4,797,140 | 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 | 1,705,962 | 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 | 1,040,995 | 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 | 47,411 | 40,687
Significant other observable inputs (Level 2) | ABS |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 1,600,967 | 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 | 156,413 | 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 | 146,670 | 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 | 99,430 | 104,154
Significant unobservable inputs (Level 3) |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturities | 64,313 | 86,679
Equity securities | 0 | 0
Other investments, at fair value | 65,707 | 65,789
Short-term investments | 0 | 0
Derivative instruments (refer to Note 5) | 0 | 0
Total Assets | 130,020 | 152,468
Derivative instruments (refer to Note 5) | 10,233 | 10,299
Cash settled awards (refer to Note 8) | 0 | 0
Total Liabilities | 10,233 | 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 | 41,125 | 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 | 11,145 | 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 | 12,043 | 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 | 47,685 | 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 | 18,022 | 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 | 630,194 | 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 | 184,747 | 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 | 272,752 | 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 | 61,526 | 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 | 111,169 | 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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