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INVESTMENTS | 12 Months Ended
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Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract] |
INVESTMENTS |
a) | Fixed Maturities and Equities
The amortized cost or cost and fair values of the Company's fixed maturities and equities were as follows:
|  | Amortized Cost or Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Value |  | Non-credit OTTI in AOCI(5) |
| At December 31, 2017 |  |  |  |  |  |  |  |  |  |
| Fixed maturities |  |  |  |  |  |  |  |  |  |
| U.S. government and agency | $ | 1,727,643 |  |  | $ | 1,735 |  |  | $ | (16,909 | ) |  | $ | 1,712,469 |  |  | $ | — |  |
| Non-U.S. government | 798,582 |  |  | 17,240 |  |  | (9,523 | ) |  | 806,299 |  |  | — |  |
| Corporate debt | 5,265,795 |  |  | 61,922 |  |  | (29,851 | ) |  | 5,297,866 |  |  | — |  |
| Agency RMBS(1) | 2,414,720 |  |  | 8,132 |  |  | (27,700 | ) |  | 2,395,152 |  |  | — |  |
| CMBS(2) | 776,715 |  |  | 4,138 |  |  | (3,125 | ) |  | 777,728 |  |  | — |  |
| Non-Agency RMBS | 45,713 |  |  | 1,917 |  |  | (799 | ) |  | 46,831 |  |  | (853 | ) |
| ABS(3) | 1,432,884 |  |  | 5,391 |  |  | (1,994 | ) |  | 1,436,281 |  |  | — |  |
| Municipals(4) | 149,167 |  |  | 1,185 |  |  | (972 | ) |  | 149,380 |  |  | — |  |
| Total fixed maturities | $ | 12,611,219 |  |  | $ | 101,660 |  |  | $ | (90,873 | ) |  | $ | 12,622,006 |  |  | $ | (853 | ) |
| Equity securities |  |  |  |  |  |  |  |  |  |
| Common stocks | $ | 22,836 |  |  | $ | 3,412 |  |  | $ | (590 | ) |  | $ | 25,658 |  |  |  |
| Exchange-traded funds | 356,252 |  |  | 71,675 |  |  | (294 | ) |  | 427,633 |  |  |  |
| Bond mutual funds | 173,779 |  |  | 9,440 |  |  | (999 | ) |  | 182,220 |  |  |  |
| Total equity securities | $ | 552,867 |  |  | $ | 84,527 |  |  | $ | (1,883 | ) |  | $ | 635,511 |  |  |  |
| At December 31, 2016 |  |  |  |  |  |  |  |  |  |
| Fixed maturities |  |  |  |  |  |  |  |  |  |
| U.S. government and agency | $ | 1,681,425 |  |  | $ | 1,648 |  |  | $ | (27,004 | ) |  | $ | 1,656,069 |  |  | $ | — |  |
| Non-U.S. government | 613,282 |  |  | 2,206 |  |  | (49,654 | ) |  | 565,834 |  |  | — |  |
| Corporate debt | 4,633,834 |  |  | 42,049 |  |  | (75,140 | ) |  | 4,600,743 |  |  | — |  |
| Agency RMBS(1) | 2,487,837 |  |  | 13,275 |  |  | (35,977 | ) |  | 2,465,135 |  |  | — |  |
| CMBS(2) | 664,368 |  |  | 5,433 |  |  | (3,564 | ) |  | 666,237 |  |  | — |  |
| Non-Agency RMBS | 57,316 |  |  | 1,628 |  |  | (2,023 | ) |  | 56,921 |  |  | (823 | ) |
| ABS(3) | 1,221,813 |  |  | 3,244 |  |  | (2,843 | ) |  | 1,222,214 |  |  | — |  |
| Municipals(4) | 163,441 |  |  | 1,510 |  |  | (990 | ) |  | 163,961 |  |  | — |  |
| Total fixed maturities | $ | 11,523,316 |  |  | $ | 70,993 |  |  | $ | (197,195 | ) |  | $ | 11,397,114 |  |  | $ | (823 | ) |
| Equity securities |  |  |  |  |  |  |  |  |  |
| Common stocks | $ | 379 |  |  | $ | 41 |  |  | $ | (342 | ) |  | $ | 78 |  |  |  |
| Exchange-traded funds | 463,936 |  |  | 53,405 |  |  | (2,634 | ) |  | 514,707 |  |  |  |
| Bond mutual funds | 133,051 |  |  | — |  |  | (9,092 | ) |  | 123,959 |  |  |  |
| Total equity securities | $ | 597,366 |  |  | $ | 53,446 |  |  | $ | (12,068 | ) |  | $ | 638,744 |  |  |  |
(1) | Residential mortgage-backed securities (RMBS) originated by U.S. government-sponsored agencies.
(2) | Commercial mortgage-backed securities (CMBS).
(3) | Asset-backed securities (ABS) include debt tranched securities collateralized primarily by auto loans, student loans, credit cards, and other asset types. This asset class also includes collateralized loan obligations (CLOs) and collateralized debt obligations (CDOs).
(4) | Municipals include bonds issued by states, municipalities and political subdivisions.
(5) | Represents the non-credit component of the other-than-temporary impairment (OTTI) losses, adjusted for subsequent sales, maturities and redemptions. It does not include the change in fair value subsequent to the impairment measurement date.
In the normal course of investing activities, the Company actively manages allocations to non-controlling tranches of structured securities (variable interests) issued by Variable Interest Entities ("VIEs"). These structured securities include RMBS, CMBS and ABS and are included in the above table. Additionally, within the other investments portfolio, the Company also invests in limited partnerships (hedge funds, direct lending funds, private equity funds and real estate funds) and CLO equity tranched securities, which are all variable interests issued by VIEs (see Note 6(c) 'Other Investments'). For these variable interests, the Company does not have the power to direct the activities that are most significant to the economic performance of the VIEs therefore the Company is not the primary beneficiary of any of these VIEs. The maximum exposure to loss on these interests is limited to the amount of investment by the Company. The Company has not provided financial or other support with respect to these structured securities other than the original investment. Contractual Maturities The contractual maturities of fixed maturities are shown below. Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.
|  | Amortized Cost |  | Fair Value |  | % of Total Fair Value |
| At December 31, 2017 |  |  |  |  |  |
| Maturity |  |  |  |  |  |
| Due in one year or less | $ | 486,659 |  |  | $ | 484,663 |  |  | 3.8 | % |
| Due after one year through five years | 4,906,207 |  |  | 4,912,189 |  |  | 38.9 | % |
| Due after five years through ten years | 2,338,964 |  |  | 2,350,433 |  |  | 18.6 | % |
| Due after ten years | 209,357 |  |  | 218,729 |  |  | 1.7 | % |
|  | 7,941,187 |  |  | 7,966,014 |  |  | 63.0 | % |
| Agency RMBS | 2,414,720 |  |  | 2,395,152 |  |  | 19.0 | % |
| CMBS | 776,715 |  |  | 777,728 |  |  | 6.2 | % |
| Non-Agency RMBS | 45,713 |  |  | 46,831 |  |  | 0.4 | % |
| ABS | 1,432,884 |  |  | 1,436,281 |  |  | 11.4 | % |
| Total | $ | 12,611,219 |  |  | $ | 12,622,006 |  |  | 100.0 | % |
| At December 31, 2016 |  |  |  |  |  |
| Maturity |  |  |  |  |  |
| Due in one year or less | $ | 313,287 |  |  | $ | 305,972 |  |  | 2.8 | % |
| Due after one year through five years | 3,906,190 |  |  | 3,850,149 |  |  | 33.8 | % |
| Due after five years through ten years | 2,546,299 |  |  | 2,510,975 |  |  | 22.0 | % |
| Due after ten years | 326,206 |  |  | 319,511 |  |  | 2.8 | % |
|  | 7,091,982 |  |  | 6,986,607 |  |  | 61.4 | % |
| Agency RMBS | 2,487,837 |  |  | 2,465,135 |  |  | 21.6 | % |
| CMBS | 664,368 |  |  | 666,237 |  |  | 5.8 | % |
| Non-Agency RMBS | 57,316 |  |  | 56,921 |  |  | 0.5 | % |
| ABS | 1,221,813 |  |  | 1,222,214 |  |  | 10.7 | % |
| Total | $ | 11,523,316 |  |  | $ | 11,397,114 |  |  | 100.0 | % |
Gross Unrealized Losses The following table summarizes fixed maturities and equities in an unrealized loss position and the aggregate fair value and gross unrealized loss by length of time the security has continuously been in an unrealized loss position:
|  | 12 months or greater |  | Less than 12 months |  | Total |
|  | Fair Value |  | Unrealized Losses |  | Fair Value |  | Unrealized Losses |  | Fair Value |  | Unrealized Losses |
| At December 31, 2017 |  |  |  |  |  |  |  |  |  |  |  |
| Fixed maturities |  |  |  |  |  |  |  |  |  |  |  |
| U.S. government and agency | $ | 194,916 |  |  | $ | (5,963 | ) |  | $ | 1,389,792 |  |  | $ | (10,946 | ) |  | $ | 1,584,708 |  |  | $ | (16,909 | ) |
| Non-U.S. government | 62,878 |  |  | (6,806 | ) |  | 204,110 |  |  | (2,717 | ) |  | 266,988 |  |  | (9,523 | ) |
| Corporate debt | 407,300 |  |  | (11,800 | ) |  | 2,041,845 |  |  | (18,051 | ) |  | 2,449,145 |  |  | (29,851 | ) |
| Agency RMBS | 759,255 |  |  | (17,453 | ) |  | 1,172,313 |  |  | (10,247 | ) |  | 1,931,568 |  |  | (27,700 | ) |
| CMBS | 31,607 |  |  | (703 | ) |  | 348,943 |  |  | (2,422 | ) |  | 380,550 |  |  | (3,125 | ) |
| Non-Agency RMBS | 8,029 |  |  | (788 | ) |  | 4,197 |  |  | (11 | ) |  | 12,226 |  |  | (799 | ) |
| ABS | 57,298 |  |  | (570 | ) |  | 392,170 |  |  | (1,424 | ) |  | 449,468 |  |  | (1,994 | ) |
| Municipals | 11,230 |  |  | (269 | ) |  | 65,632 |  |  | (703 | ) |  | 76,862 |  |  | (972 | ) |
| Total fixed maturities | $ | 1,532,513 |  |  | $ | (44,352 | ) |  | $ | 5,619,002 |  |  | $ | (46,521 | ) |  | $ | 7,151,515 |  |  | $ | (90,873 | ) |
| Equity securities |  |  |  |  |  |  |  |  |  |  |  |
| Common stocks | $ | — |  |  | $ | — |  |  | $ | 3,202 |  |  | $ | (590 | ) |  | $ | 3,202 |  |  | $ | (590 | ) |
| Exchange-traded funds | — |  |  | — |  |  | 12,323 |  |  | (294 | ) |  | 12,323 |  |  | (294 | ) |
| Bond mutual funds | — |  |  | — |  |  | 12,184 |  |  | (999 | ) |  | 12,184 |  |  | (999 | ) |
| Total equity securities | $ | — |  |  | $ | — |  |  | $ | 27,709 |  |  | $ | (1,883 | ) |  | $ | 27,709 |  |  | $ | (1,883 | ) |
| At December 31, 2016 |  |  |  |  |  |  |  |  |  |  |  |
| Fixed maturities |  |  |  |  |  |  |  |  |  |  |  |
| U.S. government and agency | $ | 54,051 |  |  | $ | (2,729 | ) |  | $ | 1,340,719 |  |  | $ | (24,275 | ) |  | $ | 1,394,770 |  |  | $ | (27,004 | ) |
| Non-U.S. government | 149,360 |  |  | (38,683 | ) |  | 283,796 |  |  | (10,971 | ) |  | 433,156 |  |  | (49,654 | ) |
| Corporate debt | 230,218 |  |  | (30,652 | ) |  | 1,948,976 |  |  | (44,488 | ) |  | 2,179,194 |  |  | (75,140 | ) |
| Agency RMBS | 76,694 |  |  | (1,101 | ) |  | 1,724,170 |  |  | (34,876 | ) |  | 1,800,864 |  |  | (35,977 | ) |
| CMBS | 84,640 |  |  | (749 | ) |  | 193,499 |  |  | (2,815 | ) |  | 278,139 |  |  | (3,564 | ) |
| Non-Agency RMBS | 13,642 |  |  | (1,752 | ) |  | 7,194 |  |  | (271 | ) |  | 20,836 |  |  | (2,023 | ) |
| ABS | 362,110 |  |  | (1,950 | ) |  | 266,763 |  |  | (893 | ) |  | 628,873 |  |  | (2,843 | ) |
| Municipals | 774 |  |  | (29 | ) |  | 68,598 |  |  | (961 | ) |  | 69,372 |  |  | (990 | ) |
| Total fixed maturities | $ | 971,489 |  |  | $ | (77,645 | ) |  | $ | 5,833,715 |  |  | $ | (119,550 | ) |  | $ | 6,805,204 |  |  | $ | (197,195 | ) |
| Equity securities |  |  |  |  |  |  |  |  |  |  |  |
| Common stocks | $ | — |  |  | $ | — |  |  | $ | 37 |  |  | $ | (342 | ) |  | $ | 37 |  |  | $ | (342 | ) |
| Exchange-traded funds | 4,959 |  |  | (461 | ) |  | 87,760 |  |  | (2,173 | ) |  | 92,719 |  |  | (2,634 | ) |
| Bond mutual funds | — |  |  | — |  |  | 123,954 |  |  | (9,092 | ) |  | 123,954 |  |  | (9,092 | ) |
| Total equity securities | $ | 4,959 |  |  | $ | (461 | ) |  | $ | 211,751 |  |  | $ | (11,607 | ) |  | $ | 216,710 |  |  | $ | (12,068 | ) |
Fixed Maturities At December 31, 2017, 2,424 fixed maturities (2016: 1,881) were in an unrealized loss position of $91 million (2016: $197 million) of which $7 million (2016: $15 million) was related to securities below investment grade or not rated. At December 31, 2017, 627 securities (2016: 330) had been in a continuous unrealized loss position for 12 months or greater and had a fair value of $1,533 million (2016: $971 million). Following a credit impairment review, it was concluded that these securities as well as the remaining securities in an unrealized loss position in the above table were temporarily impaired at December 31, 2017, and were expected to recover in value as the securities approach maturity. Further, at December 31, 2017, the Company did not intend to sell these securities in an unrealized loss position and it is more likely than not that the Company will not be required to sell these securities before the anticipated recovery of their amortized costs. Equity Securities At December 31, 2017, 29 securities (2016: 23) were in an unrealized loss position of $2 million (2016: $12 million). At December 31, 2017, there were no securities (2016: 3 securities) in a continuous unrealized loss position for 12 months or greater. Based on the impairment review process and the ability and intent to hold these securities for a reasonable period of time sufficient for a full recovery, the Company concluded that the above equities in an unrealized loss position were temporarily impaired at December 31, 2017.
b) | Mortgage Loans
The following table provides a breakdown of the Company's mortgage loans held-for-investment:
|  | December 31, 2017 |  | December 31, 2016 |
|  | Carrying Value |  | % of Total |  | Carrying Value |  | % of Total |
| Mortgage Loans held-for-investment: |  |  |  |  |  |  |  |
| Commercial | $ | 325,062 |  |  | 100 | % |  | $ | 349,969 |  |  | 100 | % |
|  | 325,062 |  |  | 100 | % |  | 349,969 |  |  | 100 | % |
| Valuation allowances | — |  |  | — | % |  | — |  |  | — | % |
| Total Mortgage Loans held-for-investment | $ | 325,062 |  |  | 100 | % |  | $ | 349,969 |  |  | 100 | % |
For commercial mortgage loans, the primary credit quality indicator is the debt service coverage ratio (which compares a property’s net operating income to amounts needed to service the principal and interest due under the loan, generally, the lower the debt service coverage ratio, the higher the risk of experiencing a credit loss) and the loan-to-value ratio (loan-to-value ratios compare the unpaid principal balance of the loan to the estimated fair value of the underlying collateral, generally, the higher the loan-to-value ratio, the higher the risk of experiencing a credit loss). The debt service coverage ratio and loan-to-value ratio, as well as the values utilized in calculating these ratios, are updated annually, on a rolling basis. The Company has a high quality mortgage loan portfolio with weighted average debt service coverage ratios in excess of 3.0 x and weighted average loan-to-value ratios of less than 60%. There are no credit losses associated with the commercial mortgage loans held by the Company at December 31, 2017. There are no past due amounts at December 31, 2017.
c) | Other Investments
The following tables provide a breakdown of the Company's other investments, together with additional information relating to the liquidity of each category:
|  | Fair Value |  | Redemption Frequency (if currently eligible) |  | Redemption Notice Period |
| At December 31, 2017 |  |  |  |  |  |  |  |
| Long/short equity funds | $ | 38,470 |  |  | 4 | % |  | Annually |  | 60 days |
| Multi-strategy funds | 286,164 |  |  | 28 | % |  | Quarterly, Semi-annually |  | 60-95 days |
| Event-driven funds | 39,177 |  |  | 4 | % |  | Annually |  | 45 days |
| Direct lending funds | 250,681 |  |  | 25 | % |  | n/a |  | n/a |
| Private equity funds | 68,812 |  |  | 7 | % |  | n/a |  | n/a |
| Real estate funds | 50,009 |  |  | 5 | % |  | n/a |  | n/a |
| CLO-Equities | 31,413 |  |  | 2 | % |  | n/a |  | n/a |
| Other privately held investments | 46,430 |  |  | 5 | % |  | n/a |  | n/a |
| Overseas deposits | 198,217 |  |  | 20 | % |  | n/a |  | n/a |
| Total other investments | $ | 1,009,373 |  |  | 100 | % |  |  |  |  |
| At December 31, 2016 |  |  |  |  |  |  |  |
| Long/short equity funds | $ | 118,619 |  |  | 14 | % |  | Semi-annually, Annually |  | 45-60 days |
| Multi-strategy funds | 285,992 |  |  | 34 | % |  | Quarterly, Semi-annually |  | 60-95 days |
| Event-driven funds | 93,539 |  |  | 11 | % |  | Annually |  | 45 days |
| Direct lending funds | 134,650 |  |  | 16 | % |  | n/a |  | n/a |
| Private equity funds | 81,223 |  |  | 10 | % |  | n/a |  | n/a |
| Real estate funds | 13,354 |  |  | 2 | % |  | n/a |  | n/a |
| CLO-Equities | 60,700 |  |  | 8 | % |  | n/a |  | n/a |
| Other privately held investments | 42,142 |  |  | 5 | % |  | n/a |  | n/a |
| Overseas deposits | — |  |  | — | % |  | n/a |  | n/a |
| Total other investments | $ | 830,219 |  |  | 100 | % |  |  |  |  |
n/a – not applicable The investment strategies for the above funds are as follows:
• | Long/short equity funds: Seek to achieve attractive returns primarily by executing an equity trading strategy involving both long and short investments in publicly-traded equities.
• | Multi-strategy funds: Seek to achieve above-market returns by pursuing multiple investment strategies to diversify risks and reduce volatility. This category includes funds of hedge funds which invest in a large pool of hedge funds across a diversified range of hedge fund strategies.
• | Event-driven funds: Seek to achieve attractive returns by exploiting situations where announced or anticipated events create opportunities.
• | Direct lending funds: Seek to achieve attractive risk-adjusted returns, including current income generation, by investing in funds which provide financing directly to borrowers.
• | Private equity funds: Seek to achieve attractive risk-adjusted returns by investing in private transactions over the course of several years.
• | Real estate funds: Seek to achieve attractive risk-adjusted returns by making and managing investments in real estate and real estate securities and businesses.
Two common redemption restrictions which may impact the Company's ability to redeem hedge funds are gates and lockups. A gate is a suspension of redemptions which may be implemented by the general partner or investment manager of the fund in order to defer, in whole or in part, the redemption request in the event the aggregate amount of redemption requests exceeds a predetermined percentage of the fund’s net assets which may otherwise hinder the general partner or investment manager’s ability to liquidate holdings in an orderly fashion in order to generate the cash necessary to fund extraordinarily large redemption payouts. A lockup period is the initial amount of time an investor is contractually required to hold the security before having the ability to redeem. During 2017 and 2016, neither of these restrictions impacted the Company's redemption requests. At December 31, 2017, $38 million (2016: $60 million), representing 11% (2016: 12%) of total hedge funds, relate to holdings where the Company is still within the lockup period. The expiration of these lockup periods range from March 2018 to March 2019. At December 31, 2017, the Company had $137 million (2016: $176 million) of unfunded commitments as a limited partner in direct lending funds. Once the full amount of committed capital has been called by the General Partner of each of these funds, the assets will not be fully returned until the completion of the fund's investment term. These funds have investment terms ranging from 5-10 years and the General Partners of certain funds have the option to extend the term by up to 3 years. At December 31, 2017, the Company had $16 million (2016: $12 million) of unfunded commitments as a limited partner in multi-strategy hedge funds. Once the full amount of committed capital has been called by the General Partner of each of these funds, the assets will not be fully returned until after the completion of the funds' investment term. These funds have investment terms ranging from 2 years to the dissolution of the underlying fund. At December 31, 2017, the Company had $115 million (2016: $140 million) of unfunded commitments as a limited partner in funds which invest in real estate and real estate securities and businesses. These funds have investment terms ranging from 7 years to the dissolution of the underlying fund. At December 31, 2017, the Company had $21 million (2016: $24 million) of unfunded commitments as a limited partner in a private equity fund. The life of the fund is subject to the dissolution of the underlying funds. The Company expects the overall holding period to be over 10 years. During 2015, the Company made a $50 million commitment as a limited partner of a bank revolver opportunity fund. The fund is subject to an investment term of 7 years and the General Partners have the option to extend the term by up to 2 years. At December 31, 2017, this commitment remains unfunded. It is not anticipated that the full amount of this fund will be drawn. During 2017, the Company made a $75 million commitment as a limited partner of an open-ended commercial mortgage income fund. At December 31, 2017, this commitment remains unfunded. Syndicate 2007 holds overseas deposits which include investments in private funds in which the underlying investments are primarily U.S. government, Non-U.S. government and corporate fixed maturities. The funds do not trade on an exchange therefore are not included within available for sale investments.
d) | Equity Method Investments
During 2016, the Company paid $108 million including direct transaction costs to acquire 19% of the common equity of Harrington Reinsurance Holdings Limited ("Harrington"), the parent company of Harrington Re Ltd. ("Harrington Re"), an independent reinsurance company jointly sponsored by AXIS Capital and The Blackstone Group L.P. ("Blackstone"). Through long-term service agreements, AXIS Capital will serve as Harrington Re's reinsurance underwriting manager and Blackstone will serve as exclusive investment management service provider. As an investor, the Company expects to benefit from underwriting profit generated by Harrington Re and the income and capital appreciation Blackstone seeks to deliver through its investment management services. In addition, the Company has entered into an arrangement with Blackstone under which underwriting and investment related fees will be shared equally. Harrington is not a variable interest entity. Given that the Company exercises significant influence over the operating and financial policies of this investee the Company accounts for its ownership in Harrington under the equity method of accounting. The Company's proportionate share of the underlying equity in net assets resulted in a basis difference of $5 million which represents initial transactions costs. For the year ended December 31, 2017, the Company recorded an impairment charge of $9 million, related to a U.S. based insurance company, which reduced the carrying value of the investment to $nil. This charge is included in interest in loss of equity method investments in the Consolidated Statement of Operations. e) Net Investment Income Net investment income was derived from the following sources:
| Year ended December 31, | 2017 |  | 2016 |  | 2015 |
| Fixed maturities | $ | 312,662 |  |  | $ | 305,459 |  |  | $ | 294,725 |  |
| Other investments | 76,858 |  |  | 42,514 |  |  | 20,148 |  |
| Equity securities | 14,919 |  |  | 16,306 |  |  | 11,289 |  |
| Mortgage loans | 10,780 |  |  | 7,996 |  |  | 1,861 |  |
| Cash and cash equivalents | 10,057 |  |  | 9,209 |  |  | 8,572 |  |
| Short-term investments | 2,718 |  |  | 2,060 |  |  | 439 |  |
| Gross investment income | 427,994 |  |  | 383,544 |  |  | 337,034 |  |
| Investment expenses | (27,189 | ) |  | (30,209 | ) |  | (31,698 | ) |
| Net investment income | $ | 400,805 |  |  | $ | 353,335 |  |  | $ | 305,336 |  |
f) | Net Realized Investment Gains (Losses)
The following table provides an analysis of net realized investment gains (losses):
| Year ended December 31, | 2017 |  | 2016 |  | 2015 |
| Gross realized gains |  |  |  |  |  |
| Fixed maturities and short-term investments | $ | 72,046 |  |  | $ | 86,267 |  |  | $ | 60,102 |  |
| Equities | 78,343 |  |  | 19,104 |  |  | 19,113 |  |
| Gross realized gains | 150,389 |  |  | 105,371 |  |  | 79,215 |  |
| Gross realized losses |  |  |  |  |  |
| Fixed maturities and short-term investments | (98,442 | ) |  | (134,460 | ) |  | (143,702 | ) |
| Equities | (959 | ) |  | (16,155 | ) |  | (8,543 | ) |
| Gross realized losses | (99,401 | ) |  | (150,615 | ) |  | (152,245 | ) |
| Net OTTI recognized in net income | (14,493 | ) |  | (26,210 | ) |  | (72,720 | ) |
| Change in fair value of investment derivatives(1) | (8,269 | ) |  | 10,929 |  |  | 7,259 |  |
| Net realized investment gains (losses) | $ | 28,226 |  |  | $ | (60,525 | ) |  | $ | (138,491 | ) |
(1) | Refer to Note 8 'Derivative Instruments'
The following table summarizes the OTTI recognized in net income by asset class:
| Year ended December 31, | 2017 |  | 2016 |  | 2015 |
| Fixed maturities: |  |  |  |  |  |
| Non-U.S. government | $ | 8,187 |  |  | $ | 3,557 |  |  | $ | 3,538 |  |
| Corporate debt | 6,306 |  |  | 20,093 |  |  | 47,029 |  |
| Non-Agency RMBS | — |  |  | — |  |  | 111 |  |
| ABS | — |  |  | — |  |  | 124 |  |
|  | 14,493 |  |  | 23,650 |  |  | 50,802 |  |
| Equity Securities |  |  |  |  |  |
| Exchange-traded funds | — |  |  | 2,560 |  |  | 10,732 |  |
| Bond mutual funds | — |  |  | — |  |  | 11,186 |  |
|  | — |  |  | 2,560 |  |  | 21,918 |  |
| Total OTTI recognized in net income | $ | 14,493 |  |  | $ | 26,210 |  |  | $ | 72,720 |  |
Fixed Maturities The following table provides a roll forward of credit losses ("credit loss table"), before income taxes, for which a portion of the OTTI charge was recognized in AOCI:
| Year ended December 31, | 2017 |  | 2016 |
| Balance at beginning of period | $ | 1,493 |  |  | $ | 1,506 |  |
| Credit impairments recognized on securities not previously impaired | — |  |  | — |  |
| Additional credit impairments recognized on securities previously impaired | 13 |  |  | 20 |  |
| Change in timing of future cash flows on securities previously impaired | — |  |  | — |  |
| Intent to sell of securities previously impaired | — |  |  | — |  |
| Securities sold/redeemed/matured | (12 | ) |  | (33 | ) |
| Balance at end of period | $ | 1,494 |  |  | $ | 1,493 |  |
Credit losses are calculated based on the difference between the amortized cost of the security and the net present value of its projected future cash flows discounted at the effective interest rate implicit in the debt security prior to the impairment. The following provides a summary of the credit loss activities by asset class for the above table as well as the significant inputs and the methodology used to estimate these credit losses. U.S. Government, U.S. Agency and U.S. Agency RMBS: Unrealized losses on securities issued or backed (either explicitly or implicitly) by the U.S. government are not analyzed for OTTI. The Company have concluded that the possibility of any credit losses on these securities is highly unlikely due to the explicit U.S. government guarantee on certain securities (e.g. GNMA issuances) and, on others, the implicit guarantee that has been validated by past actions (e.g. U.S. government bailout of FNMA and FHLMC during the 2008 credit crisis). Although not analyzed for credit losses, the securities are still evaluated for intention to sell and likely requirement to sell. Non-U.S. Government: Non-U.S. government obligations are evaluated for credit loss primarily through qualitative assessments of the likelihood of credit loss using information such as duration and severity of unrealized losses, as well as credit ratings and price volatility. At December 31, 2017, the Company's holdings in sovereign debt, including $185 million (2016: $28 million) relating to the eurozone countries, were substantially all investment-grade securities. The gross unrealized losses of $10 million at December 31, 2017 were mainly due to foreign exchange losses. Based on analysis performed, the Company does not anticipate any credit losses on non-U.S. government fixed maturities held at December 31, 2017. In 2017, the OTTI charges on non-U.S. government fixed maturities mainly related to unrealized foreign exchange losses on certain securities where forecasted recovery was uncertain. Corporate Debt: To estimate credit losses for corporate debt securities, the Company's projected cash flows are primarily driven by assumptions regarding the probability of default and the severity associated with those defaults. The Company's default and loss severity rates are based on credit rating, credit analysis, industry analyst reports and forecasts, Moody’s historical default data and any other data relevant to the recoverability of the security. In 2017, the OTTI charges on corporate debt securities were mainly related to significant loss severity, unrealized foreign exchange losses on certain securities where forecasted recovery was uncertain, as well as the Company's intent to sell. CMBS: The Company's investments in CMBS are diversified and primarily rated AA or better, with a weighted average estimated subordination percentage of 29% at December 31, 2017 (2016: 36%). Based on discounted cash flows at December 31, 2017, the current level of subordination is sufficient to cover the estimated loan losses on the underlying collateral of the CMBS. Non-agency RMBS: For non-agency RMBS, the Company's projected cash flows incorporated underlying data from widely accepted third-party data sources along with certain internal assumptions and judgments regarding the future performance of the security. These assumptions included the following: default, delinquency, loss severity and prepayment rates. The assumptions used to calculate the credit losses in 2017 have not changed significantly since December 31, 2016. At December 31, 2017, the fair value of the Company's non-agency RMBS was $47 million (2016: $57 million), consisting primarily of $34 million (2016: $40 million) of Prime and $8 million (2016: $10 million) of Alt-A MBS. The Company has concluded there are no credit losses anticipated for any of its non-agency RMBS at December 31, 2017, other than those already recorded. ABS: The Company's investments in ABS at December 31, 2017 consist mainly of CLO debt tranched securities ("CLO Debt") purchased primarily as new issues during 2015 through 2017. Of these new issues all had credit ratings of AA or better. The Company utilizes a scenario-based approach to reviewing the CLO Debt portfolio based on the current asset market price. The Company also reviews subordination levels of its securities to determine their ability to absorb credit losses of underlying collateral. If losses are forecast to be below the subordination level for the tranche held by the Company, the security is determined not to be impaired. The Company has concluded that there are no credit losses anticipated for any CLO Debt at December 31, 2017. Equity Securities There were no OTTI losses on equity securities in 2017. The OTTI losses on equity securities in 2016 are primarily due to the severity of their unrealized loss positions, for which the Company concluded the forecast recovery period was uncertain. The recognition of such losses does not necessarily indicate that sales will occur or that sales are imminent or planned. At December 31, 2017, the fair value of the Company's equities was $636 million (2016: $639 million), which included $2 million (2016: $12 million) of gross unrealized losses.
g) | Restricted Assets
In order to support the Company's obligations in regulatory jurisdictions where it operates as a non-admitted carrier, the Company provides collateral in the form of assets held in trust and, to a lesser extent, letters of credit (see Note 11(b) 'Debt and Financing Arrangement s'). In addition, the Company operates in the Lloyd’s market through its corporate member AXIS Corporate Capital UK Limited, which represents its participation in Syndicate 1686 and Novae Corporate Underwriting Limited, the sole corporate member of Syndicate 2007. Lloyd’s sets capital requirements for corporate members annually through the application of a capital model that is based on regulatory rules pursuant to Directive 2009/138/EC of the European Parliament and of the Council of 25 November 2009 on the taking up and pursuit of business of Insurance and Reinsurance (Solvency II) ("Solvency II"). The capital provided to support underwriting, or Funds at Lloyd’s ("FAL"), may be satisfied by cash, certain investments and letters of credit provided by approved banks (see Note 12 'Commitments and Contingencies' and Note 21 'Statutory Financial Information'). Further, at December 31, 2017 collateral in trust for third party agreements included $1,120 million of fixed maturities and equity securities, and cash of $55 million held on deposit to support the underwriting activities of Syndicate 2007. At December 31, 2017 collateral in trust for third party agreements included cash of $140 million (2016: $84 million) held on deposit to support the underwriting activities of Syndicate 1686. The Company's restricted investments and cash primarily consist of high-quality fixed maturity and short-term investment securities. The fair value of the Company's restricted investments and cash primarily relates to these items, as noted in the table below.
| At December 31, |  | 2017 |  | 2016 |
| Collateral in Trust for inter-company agreements |  | $ | 3,310,180 |  |  | $ | 2,877,823 |  |
| Collateral for secured letter of credit facility |  | 386,451 |  |  | 448,366 |  |
| Funds at Lloyd's |  | 1,192,717 |  |  | 382,611 |  |
| Collateral in Trust for third party agreements |  | 2,085,443 |  |  | 508,262 |  |
| Securities on deposit with regulatory authorities |  | 53,925 |  |  | 50,290 |  |
| Total restricted investments |  | $ | 7,028,716 |  |  | $ | 4,267,352 |  |
h) | Reverse Repurchase Agreements
At December 31, 2017, the Company held $37 million (2016: $176 million) of reverse repurchase agreements. These loans are fully collateralized, are generally outstanding for a short period of time and are presented on a gross basis as part of cash and cash equivalents on the Company's consolidated balance sheet. The required collateral for these loans is either cash or U.S. Treasuries at a minimum rate of 102% of the loan principal. Upon maturity, the Company receives principal and interest income. The Company monitors the estimated fair value of the securities loaned and borrowed on a daily basis with additional collateral obtained as necessary throughout the duration of the transaction.

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