Fair value is defined as the amount that would be received for the sale of an asset or paid to transfer a liability (an exit price), in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants as of the measurement date. Applicable accounting guidance provides an established hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs that market participants would use in valuing the asset or liability and are developed based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company's assumptions about the factors that market participants would use in valuing the asset or liability. Assets and liabilities are classified based on the lowest level of input that is significant to the fair value measurements. The Company reviews the fair value hierarchy classification on a quarterly basis. Changes in the observability of valuation inputs may result in a reclassification of levels for certain securities within the fair value hierarchy.

The fair values for available for sale investments are generally sourced from third parties. The fair value of fixed income securities is based upon quoted market values where available, “evaluated bid” prices provided by third party pricing services (“pricing services”) where quoted market values are not available, or by reference to broker quotes where pricing services do not provide coverage for a particular security. While the Company receives values for the majority of the investment securities it holds from pricing services, it is ultimately management's responsibility to determine whether the values received and recorded in the financial statements are representative of appropriate fair value measurements.

The Company performs regular reviews of the prices received from its third party valuation sources to assess if the prices represent a reasonable estimate of the fair value. This process is completed by investment and accounting personnel who are independent of those responsible for obtaining the valuations. The approaches taken by the Company include, but are not limited to, annual reviews of the controls of the external parties responsible for sourcing valuations, which are subjected to automated tolerance checks, quarterly reviews of the valuation sources and dates, and monthly reconciliations between the valuations provided by our external parties and valuations provided by our third party investment managers at a portfolio level.

Where broker quotes are the primary source of the valuations, sufficient information regarding the specific inputs utilized by the brokers is generally not available to support a Level 2 classification. The Company obtains the majority of broker quoted values from third party investment managers who perform independent verifications of these valuations using pricing matrices based upon information gathered by market traders. In addition, for the majority of these securities, the Company compares the broker quotes to independent valuations obtained from third party pricing vendors, which may also consist of broker quotes, to assess if the prices received represent a reasonable estimate of the fair value.

For further information, see Item 8, Note 2, “Significant Accounting Policies,” to the Consolidated Financial Statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2011.

The following tables set forth the Company's assets and liabilities that were accounted for at fair value at September 30, 2012 and December 31, 2011 by level within the fair value hierarchy:

	Quoted Prices		Significant		Significant
	in Active		Other		Other		Collateral
	Markets for		Observable		Unobservable		and		Balance at
September 30, 2012	Identical Assets		Inputs		Inputs		Counterparty		September 30,
(U.S. dollars in thousands)	(Level 1)		(Level 2)		(Level 3)		Netting		2012
Assets
U.S. Government and Government - Related/Supported	$	-	$	2,135,368	$	-	$	-	$	2,135,368
Corporate (1) (2)		-		9,978,002		29,135		-		10,007,137
Residential mortgage-backed securities – Agency ("RMBS - Agency")		-		5,343,046		33,857		-		5,376,903
Residential mortgage-backed securities – Non-Agency ("RMBS - Non-Agency")		-		628,486		7,839		-		636,325
Commercial mortgage-backed securities ("CMBS")		-		1,001,040		33,369		-		1,034,409
Collateralized debt obligations ("CDO")		-		7,773		674,793		-		682,566
Other asset-backed securities (2)		-		1,441,381		17,163		-		1,458,544
U.S. States and political subdivisions of the States		-		1,820,105		-		-		1,820,105
Non-U.S. Sovereign Government, Provincial, Supranational and Government-Related/Supported		-		4,274,936		-		-		4,274,936
Total fixed maturities, at fair value	$	-	$	26,630,137	$	796,156	$	-	$	27,426,293
Equity securities, at fair value (3)		230,539		335,388		-		-		565,927
Short-term investments, at fair value (1)(4)		-		323,705		-		-		323,705
Total investments available for sale	$	230,539	$	27,289,230	$	796,156	$	-	$	28,315,925
Cash equivalents (5)		2,037,971		321,646		-		-		2,359,617
Other investments (6)		-		783,813		119,975		-		903,788
Other assets (7)		-		10,611		-		41,540		52,151
Total assets accounted for at fair value	$	2,268,510	$	28,405,300	$	916,131	$	41,540	$	31,631,481

Liabilities
Financial instruments sold, but not yet purchased (8)	$	-	$	30,944	$	-	$	-	$	30,944
Other liabilities (7)		-		82,009		35,062		-		117,071
Total liabilities accounted for at fair value	$	-	$	112,953	$	35,062	$	-	$	148,015

	Quoted Prices		Significant		Significant
	in Active		Other		Other		Collateral
	Markets for		Observable		Unobservable		and		Balance at
December 31, 2011	Identical Assets		Inputs		Inputs		Counterparty		December 31,
(U.S. dollars in thousands)	(Level 1)		(Level 2)		(Level 3)		Netting		2011
Assets
U.S. Government and Government - Related/Supported	$	-	$	1,990,983	$	-	$	-	$	1,990,983
Corporate (1) (2)		-		10,084,804		23,818		-		10,108,622
RMBS – Agency		-		5,347,365		32,041		-		5,379,406
RMBS – Non-Agency		-		641,815		-		-		641,815
CMBS		-		974,835		-		-		974,835
CDO		-		7,751		650,851		-		658,602
Other asset-backed securities (2)		-		1,323,697		16,552		-		1,340,249
U.S. States and political subdivisions of the States		-		1,797,378		-		-		1,797,378
Non-U.S. Sovereign Government, Provincial, Supranational and Government-Related/Supported		-		3,298,135		-		-		3,298,135
Total fixed maturities, at fair value (2)	$	-	$	25,466,763	$	723,262	$	-	$	26,190,025
Equity securities, at fair value (3)		239,175		229,022		-		-		468,197
Short-term investments, at fair value (1)(4)		-		359,063		-		-		359,063
Total investments available for sale	$	239,175	$	26,054,848	$	723,262	$	-	$	27,017,285
Cash equivalents (5)		1,686,101		1,068,264		-		-		2,754,365
Other investments (6)		-		547,598		113,959		-		661,557
Other assets (7)		-		143,622		-		(77,888)		65,734
Total assets accounted for at fair value	$	1,925,276	$	27,814,332	$	837,221	$	(77,888)	$	30,498,941

Liabilities
Financial instruments sold, but not yet purchased (8)	$	-	$	20,844	$	-	$	-	$	20,844
Other liabilities (7)		-		16,871		42,644		(809)		58,706
Total liabilities accounted for at fair value	$	-	$	37,715	$	42,644	$	(809)	$	79,550

(1) Included within Corporate are certain medium term notes supported primarily by pools of European investment grade credit with varying degrees of leverage. The notes, which are in a gross unrealized loss position, had a fair value of $192.3 million and $266.0 million and an amortized cost of $199.8 million and $297.7 million at September 30, 2012 and December 31, 2011, respectively. These notes allow the investor to participate in cash flows of the underlying bonds including certain residual values, which could serve to either decrease or increase the ultimate values of these notes.

(2) The Company invests in covered bonds issued by financial institutions (“Covered Bonds”). Covered Bonds are senior secured debt instruments issued by financial institutions and backed by over-collateralized pools of public sector or mortgage loans. At September 30, 2012, Covered Bonds within Total fixed maturities with a fair value of $599.9 million are included within Other asset-backed securities to align the Company's classification to market indices. At December 31, 2011, Covered Bonds within Total fixed maturities with a fair value of $353.9 million were reclassified from Corporate to Other asset-backed securities to conform to current period presentation.

(3) Included within Equity securities are investments in fixed income funds with a fair value of $99.3 million and $91.6 million at September 30, 2012 and December 31, 2011, respectively.

(4) Short-term investments consist primarily of Corporate securities and U.S. Government and Government-Related/Supported securities.

(5) Cash equivalents balances subject to fair value measurement include certificates of deposit and money market funds. Operating cash balances are not subject to fair value measurement guidance.

(6) The Other investments balance excludes certain structured transactions including certain investments in project finance transactions, a payment obligation and liquidity financing provided to a structured credit vehicle as a part of a third party medium term note facility. These investments, which totaled $311.8 million at September 30, 2012 and $323.7 million at December 31, 2011, are carried at amortized cost. For further details regarding the nature of Other investments and related features see Item 8, Note 7, “Other Investments,” to the Consolidated Financial Statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2011

(7) Other assets and other liabilities include derivative instruments. The derivative balances included in each category are reported on a gross basis by level with a netting adjustment presented separately in the Collateral and Counterparty Netting column. The Company often enters into different types of derivative contracts with a single counterparty and these contracts are covered under a netting agreement. In addition, at September 30, 2012 the Company paid net cash collateral related to these derivative positions of $41.5 million. The assets related to the net collateral paid have been recorded as Other assets within the balance sheet. At December 31, 2011, the Company held net cash collateral of $77.1 million. The collateral balance is included within Cash and cash equivalents and the corresponding liability to return the collateral has been offset against the derivative asset within the balance sheet as appropriate under the netting agreement. The fair values of the individual derivative contracts are reported gross in their respective levels based on the fair value hierarchy.

(8) Financial instruments sold, but not yet purchased, represent “short sales” and are included within “Payable for investments purchased” on the balance sheet.

The tables below present additional information about assets and liabilities measured at fair value on a recurring basis and for which Level 3 inputs were utilized to determine fair value. The tables present a reconciliation of the beginning and ending balances for the three and nine months ended September 30, 2012 and 2011 for all financial assets and liabilities measured at fair value using significant unobservable inputs (Level 3) at September 30, 2012 and 2011, respectively. The tables do not include gains or losses that were reported in Level 3 in prior periods for assets that were transferred out of Level 3 prior to September 30, 2012 and 2011. Gains and losses for assets and liabilities classified within Level 3 in the table below may include changes in fair value that are attributable to both observable inputs (Levels 1 and 2) and unobservable inputs (Level 3). Further, it should be noted that the following tables do not take into consideration the effect of offsetting Level 1 and 2 financial instruments entered into by the Company that are either economically hedged by certain exposures to the Level 3 positions or that hedge the exposures in Level 3 positions.

In general, Level 3 assets include securities for which values were obtained from brokers where either significant inputs were utilized in determining the values that were difficult to corroborate with observable market data, or sufficient information regarding the specific inputs utilized by the broker was not available to support a Level 2 classification. Transfers into or out of Level 3 primarily arise as a result of the valuations utilized by the Company changing between either those provided by independent pricing services that do not contain significant observable inputs, or other valuations sourced from brokers that are considered Level 3.

There were no significant transfers between Level 1 and Level 2 during the three and nine month periods ended September 30, 2012 and 2011.


	Level 3 Assets and Liabilities - Three Months Ended September 30, 2012
(U.S. dollars in thousands)			Corporate		RMBS - Agency		RMBS - Non Agency		CMBS		CDO
Balance, beginning of period		$	33,511	$	52,588	$	1,596	$	-	$	642,179
Realized gains (losses)			20		4		(22)		-		913
Movement in unrealized gains (losses)			673		106		(424)		-		35,886
Purchases and issuances			-		34		6,821		33,369		-
Sales and settlements			(555)		(4,645)		(59)		-		(5,347)
Transfers into Level 3			-		-		-		-		1,162
Transfers out of Level 3			(4,514)		(14,230)		(73)		-		-
Fixed maturities to short-term investments classification change			-		-		-		-		-
Balance, end of period		$	29,135	$	33,857	$	7,839	$	33,369	$	674,793
Movement in total gains (losses) above relating to instruments still held at the reporting date		$	674	$	110	$	(447)	$	-	$	35,806


	Level 3 Assets and Liabilities - Three Months Ended September 30, 2012
(U.S. dollars in thousands)			Other asset-backed securities		Non-US Sovereign Government, Provincial, Supranational and Government Related/Supported		Short-term investments		Other investments		Derivative Contracts - Net
Balance, beginning of period		$	25,248	$	-	$	-	$	117,765	$	(35,947)
Realized gains (losses)			7,017		-		-		343		-
Movement in unrealized gains (losses)			(6,552)		-		-		1,686		885
Purchases and issuances			8,753		-		-		982		-
Sales and settlements			(16,141)		-		-		(807)		-
Transfers into Level 3			-		-		-		6		-
Transfers out of Level 3			(1,162)		-		-		-		-
Fixed maturities to short-term investments classification change			-		-		-		-		-
Balance, end of period		$	17,163	$	-	$	-	$	119,975	$	(35,062)
Movement in total gains (losses) above relating to instruments still held at the reporting date		$	456	$	-	$	-	$	1,334	$	885


	Level 3 Assets and Liabilities - Three Months Ended September 30, 2011
(U.S. dollars in thousands)			Corporate		RMBS - Agency		RMBS - Non Agency		CMBS		CDO
Balance, beginning of period		$	4,786	$	15,385	$	3,194	$	4,563	$	727,239
Realized gains (losses)			23		(81)		(328)		(501)		(2,662)
Movement in unrealized gains (losses)			(22)		52		76		564		(46,520)
Purchases and issuances			-		33		-		-		-
Sales and settlements			-		(206)		(143)		(232)		(12,215)
Transfers into Level 3			-		-		-		-		-
Transfers out of Level 3			-		-		-		-		-
Fixed maturities to short-term investments classification change			-		-		-		-		-
Balance, end of period		$	4,787	$	15,183	$	2,799	$	4,394	$	665,842
Movement in total gains (losses) above relating to instruments still held at the reporting date		$	1	$	(29)	$	(252)	$	63	$	(49,432)


	Level 3 Assets and Liabilities - Three Months Ended September 30, 2011
(U.S. dollars in thousands)			Other asset-backed securities		Non-US Sovereign Government, Provincial, Supranational and Government Related/Supported		Short-term investments		Other investments		Derivative Contracts - Net
Balance, beginning of period		$	17,048	$	-	$	-	$	114,540	$	(49,645)
Realized gains (losses)			(238)		-		-		(244)		-
Movement in unrealized gains (losses)			302		-		-		2,642		(2,344)
Purchases and issuances			-		-		-		1,667		-
Sales and settlements			-		-		-		(4,243)		-
Transfers into Level 3			-		-		-		-		-
Transfers out of Level 3			-		-		-		-		-
Fixed maturities to short-term investments classification change			-		-		-		-		-
Balance, end of period		$	17,112	$	-	$	-	$	114,362	$	(51,989)
Movement in total gains (losses) above relating to instruments still held at the reporting date		$	64	$	-	$	-	$	2,398	$	(2,344)


	Level 3 Assets and Liabilities - Nine Months Ended September 30, 2012
(U.S. dollars in thousands)			Corporate		RMBS - Agency		RMBS - Non Agency		CMBS		CDO
Balance, beginning of period		$	23,818	$	32,041	$	-	$	-	$	650,851
Realized gains (losses)			4		(23)		-		-		(523)
Movement in unrealized gains (losses)			346		58		-		-		75,489
Purchases and issuances			8,949		103		6,821		33,369		-
Sales and settlements			(181)		(6,233)		-		-		(51,024)
Transfers into Level 3			838		15,254		1,018		-		-
Transfers out of Level 3			(4,639)		(7,343)		-		-		-
Fixed maturities to short-term investments classification change			-		-		-		-		-
Balance, end of period		$	29,135	$	33,857	$	7,839	$	33,369	$	674,793
Movement in total gains (losses) above relating to instruments still held at the reporting date		$	351	$	35	$	-	$	-	$	71,738


	Level 3 Assets and Liabilities - Nine Months Ended September 30, 2012
(U.S. dollars in thousands)			Other asset-backed securities		Non-US Sovereign Government, Provincial, Supranational and Government Related/Supported		Short-term investments		Other investments		Derivative Contracts - Net
Balance, beginning of period		$	16,552	$	-	$	-	$	113,959	$	(42,644)
Realized gains (losses)			6,748		-		-		2,782		-
Movement in unrealized gains (losses)			(2,873)		-		-		6,206		7,582
Purchases and issuances			8,753		-		-		4,664		-
Sales and settlements			(15,867)		-		-		(7,327)		-
Transfers into Level 3			3,850		-		-		6		-
Transfers out of Level 3			-		-		-		(315)		-
Fixed maturities to short-term investments classification change			-		-		-		-		-
Balance, end of period		$	17,163	$	-	$	-	$	119,975	$	(35,062)
Movement in total gains (losses) above relating to instruments still held at the reporting date		$	3,652	$	-	$	-	$	2,385	$	7,582


	Level 3 Assets and Liabilities - Nine Months Ended September 30, 2011
(U.S. dollars in thousands)			Corporate		RMBS - Agency		RMBS - Non Agency		CMBS		CDO
Balance, beginning of period		$	36,866	$	30,255	$	4,964	$	1,623	$	721,572
Realized gains (losses)			(257)		(81)		(329)		(1,179)		(3,733)
Movement in unrealized gains (losses)			173		2		61		1,078		(10,104)
Purchases and issuances			6,878		33		-		3,155		2,379
Sales and settlements			(10,049)		(492)		(517)		(283)		(46,158)
Transfers into Level 3			-		-		-		-		1,886
Transfers out of Level 3			(28,824)		(14,534)		(1,380)		-		-
Fixed maturities to short-term investments classification change			-		-		-		-		-
Balance, end of period		$	4,787	$	15,183	$	2,799	$	4,394	$	665,842
Movement in total gains (losses) above relating to instruments still held at the reporting date		$	(52)	$	(79)	$	(268)	$	(855)	$	(15,656)


	Level 3 Assets and Liabilities - Nine Months Ended September 30, 2011
(U.S. dollars in thousands)			Other asset-backed securities		Non-US Sovereign Government, Provincial, Supranational and Government Related/Supported		Short-term investments		Other investments		Derivative Contracts - Net
Balance, beginning of period		$	24,650	$	3,667	$	-	$	133,717	$	(39,195)
Realized gains (losses)			(555)		-		-		11,911		-
Movement in unrealized gains (losses)			7,162		-		-		10,134		(12,620)
Purchases and issuances			-		-		-		9,782		-
Sales and settlements			(9,114)		-		-		(51,182)		(174)
Transfers into Level 3			-		-		-		-		-
Transfers out of Level 3			(5,031)		(3,667)		-		-		-
Fixed maturities to short-term investments classification change			-		-		-		-		-
Balance, end of period		$	17,112	$	-	$	-	$	114,362	$	(51,989)
Movement in total gains (losses) above relating to instruments still held at the reporting date		$	6,287	$	-	$	-	$	19,735	$	(12,620)

The Company's Level 3 assets consist primarily of CDOs, for which non-binding broker quotes are the primary source of the valuations. Sufficient information regarding the specific inputs utilized by the brokers was not available to support a Level 2 classification. The Company obtains the majority of broker quotes for these CDOs from third party investment managers who perform independent verifications of these valuations using pricing matrices based upon information gathered by market traders. In addition, for the majority of these securities, the Company compares the broker quotes to independent valuations obtained from third party pricing vendors, which may also consist of broker quotes, to assess if the prices received represent a reasonable estimate of the fair value. Although the Company does not have access to the specific unobservable inputs that may have been used in the fair value measurements of the CDO securities provided by brokers, we would expect that the significant inputs considered are prepayment rates, probability of default, loss severity in the event of default, recovery rates, liquidity premium and reinvestment rates. Significant increases (decreases) in any of those inputs in isolation could result in a significantly different fair value measurement. Generally, a change in the assumption used for the probability of default is accompanied by a directionally similar change in the assumption used for the loss severity and a directionally opposite change in the assumption used for prepayment rates.

The remainder of the Level 3 assets relate to primarily to private equity investments and certain derivative positions as described below.

Included within the Other investments component of the Company's Level 3 valuations are private investments and alternative fund investments where the Company is not deemed to have significant influence over the investee. The fair value of these investments is based upon net asset values received from the investment manager or general partner of the respective entity. The nature of the underlying investments held by the investee that form the basis of the net asset value include assets such as private business ventures and are such that significant Level 3 inputs are utilized in the determination of the individual underlying holding values and, accordingly, the fair value of the Company's investment in each entity is classified within Level 3. The Company has not adjusted the net asset values received; however, management incorporates factors such as the most recent financial information received, annual audited financial statements and the values at which capital transactions with the investee take place when applying judgment regarding whether any adjustments should be made to the net asset value in recording the fair value of each position. Investments in alternative funds included in Other investments utilize strategies including arbitrage, directional, event driven and multi-style. These funds potentially have lockup and gate provisions which may limit redemption liquidity. For further details regarding the nature of Other investments and related features see Item 8, Note 7, “Other Investments,” to the Consolidated Financial Statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2011.

Derivative instruments recorded within Other liabilities and classified within Level 3 include credit derivatives sold providing protection on senior tranches of structured finance transactions where the value is obtained directly from the investment bank counterparty and sufficient information regarding the inputs utilized in such valuation was not obtained to support a Level 2 classification and guaranteed minimum income benefits (“GMIB”) embedded within one reinsurance contract. The majority of inputs utilized in the valuations of these types of derivative contracts are considered Level 1 or Level 2; however, each valuation includes at least one Level 3 input that was significant to the valuation and, accordingly, the values are disclosed within Level 3.

Authoritative guidance over disclosures about the fair value of financial instruments requires additional disclosure of fair value information for financial instruments not carried at fair value in both interim and annual reporting periods. Certain financial instruments, particularly insurance contracts, are excluded from these fair value disclosure requirements. The carrying values of cash and cash equivalents, accrued investment income, net receivable from investments sold, other assets, net payable for investments purchased, other liabilities and other financial instruments not included below approximated their fair values. The following table includes financial instruments for which the carrying value differs from the estimated fair values at September 30, 2012 and December 31, 2011. All of these fair values estimates are considered Level 2 fair value measurements. The fair values for fixed maturities held to maturity are provided by third party pricing vendors and significant valuation inputs for all other items included were based upon market data obtained from sources independent of the Company, and are subject to the same control environment previously described.

		September 30, 2012				December 31, 2011
			Carrying		Fair		Carrying		Fair
(U.S. dollars in thousands)			Value		Value		Value		Value
	Fixed maturities, held to maturity	$	2,805,796	$	3,222,900	$	2,668,978	$	2,895,688
	Other investments - structured transactions.		311,767		287,136		323,705		297,124
Financial Assets		$	3,117,563	$	3,510,036	$	2,992,683	$	3,192,812

	Deposit liabilities	$	1,561,076	$	1,885,194	$	1,608,108	$	1,809,812
	Notes payable and debt		1,673,350		1,866,084		2,275,327		2,340,148
Financial Liabilities		$	3,234,426	$	3,751,278	$	3,883,435	$	4,149,960

The Company historically participated in structured transactions. Remaining structured transactions include cash loans supporting project finance transactions, providing liquidity facility financing to structured project deals and an investment in a payment obligation with an insurance company. These transactions are carried at amortized cost. The fair value of these investments held by the Company is determined through use of internal models utilizing reported trades, benchmark yields, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data.

Deposit liabilities include obligations under structured insurance and reinsurance transactions. For purposes of fair value disclosures, the Company determined the estimated fair value of the deposit liabilities by assuming a discount rate equal to the appropriate U.S. Treasury rate plus 102.3 basis points at September 30, 2012 and the appropriate U.S. Treasury rate plus 161.8 basis points at December 31, 2011. The discount rate incorporates the Company's own credit risk into the determination of estimated fair value.

The fair values of the Company's notes payable and debt outstanding were determined based on quoted market prices.

There are no significant concentrations of credit risk within the Company's financial instruments as defined in the authoritative guidance over disclosures of fair value of financial instruments not carried at fair value, which excludes certain financial instruments, particularly insurance contracts.