Loss Reserves for our reinsurance operations are comprised of (1) case reserves for claims reported, (2) additional case reserves ("ACRs") and (3) IBNR reserves. Our reinsurance operations receive reports of claims notices from ceding companies and record case reserves based upon the amount of reserves recommended by the ceding company. Case reserves on known events may be supplemented by ACRs, which are often estimated by our reinsurance operations' claims personnel ahead of official notification from the ceding company, or when our reinsurance operations' judgment regarding the size or severity of the known event differs from the ceding company. In certain instances, our reinsurance operations establish ACRs even when the ceding company does not report any liability on a known event. In addition, specific claim information reported by ceding companies or obtained
through claim audits can alert our reinsurance operations to emerging trends such as changing legal interpretations of coverage and liability, claims from unexpected sources or classes of business, and significant changes in the frequency or severity of individual claims. Such information is often used in the process of estimating IBNR reserves.
Deferred income taxes reflect the expected future tax consequences of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and amounts used for income tax purposes. A valuation allowance is recorded if it is more likely than not that some or all of a deferred income tax asset may not be realized. We consider future taxable income and feasible tax planning strategies in assessing the need for a valuation allowance. In the event we determine that we will not be able to realize all or part of our deferred income tax assets in the future, an adjustment to the deferred income tax assets would be charged to income in the period in which such determination is made. In addition, if we subsequently assess that the valuation allowance is no longer needed, a benefit would be recorded to income in the period in which such determination is made.
Premiums Written. Gross premiums written by the insurance segment were $2.49 billion for 2008, compared to $2.66 billion for 2007, and ceded premiums written were 33.5% of gross premiums written for 2008, compared to 35.4% for 2007. Net premiums written by the insurance segment were $1.66 billion for 2008, compared to $1.72 billion for 2007. The insurance segment continued to maintain underwriting discipline in response to the current market environment with reductions across most specialty lines of business. For information regarding net premiums written by major line of business and geographic location, refer to note 3, "Segment Information," of the notes accompanying our consolidated financial statements.
ACGL will be subject to U.S. federal income tax only to the extent that it derives U.S. source income that is subject to U.S. withholding tax or income that is effectively connected with the conduct of a trade or business within the U.S. and is not exempt from U.S. tax under an applicable income tax treaty. ACGL will be subject to a withholding tax on dividends from U.S. investments and interest from certain U.S. taxpayers. ACGL does not consider itself to be engaged in a trade or business within the U.S. and, consequently, does not expect to be subject to direct U.S. income taxation. However, because there is uncertainty as to the activities which constitute being engaged in a trade or business within the United States, there can be no assurances that the U.S. Internal Revenue Service will not contend successfully that ACGL or its non-U.S. subsidiaries are engaged in a trade or business in the United States. If ACGL or any of its non-U.S. subsidiaries were subject to U.S. income tax, ACGL's shareholders' equity and earnings could be materially adversely affected. ACGL has subsidiaries and branches that operate in various jurisdictions around the world that are subject to tax in the jurisdictions in which they operate. The significant jurisdictions in which ACGL's subsidiaries and branches are subject to tax are the United States, United Kingdom, Ireland, Canada, Switzerland, Germany and Denmark. See "Risk Factors-Risks Relating to Taxation" and "Business-Tax Matters."
The reinsurance segment's underwriting income was $318.5 million for 2007, compared to $290.6 million for 2006. The combined ratio for the reinsurance segment was 74.5% for 2007, compared to 80.7% for 2006. The components of the reinsurance segment's underwriting income are discussed below.
Ceded premiums written by the reinsurance segment were 22.0% of gross premiums written for 2007, compared to 19.9% for 2006. The higher ceded percentage in 2007 primarily resulted from the $311.4 million of premiums written ceded by Arch Re Bermuda to Flatiron ($282.2 million on an earned basis), compared to $273.2 million in 2006 ($157.4 million on an earned basis).
As a result of recent financial market disruption, which has included a lack of liquidity in the credit markets and a widening of credit spreads on fixed maturities, the market value of our investment portfolio at December 31, 2008 was lower than in prior periods.
See "Management's Discussion and Analysis of Financial Condition and Results of Operations-Critical Accounting Policies, Estimates and Recent Accounting Pronouncements-Reserves for Losses and Loss Adjustment Expenses" and "Business-Reserves" for further details.
The following table presents the calculation of book value per common share at December 31, 2008 and 2007:
For our natural catastrophe exposed business, we seek to limit the amount of exposure we will assume from any one insured or reinsured and the amount of the exposure to catastrophe losses from a single event in any geographic zone. We monitor our exposure to catastrophic events, including earthquake and wind and periodically reevaluate the estimated probable maximum pre-tax loss for such exposures. Our estimated probable maximum pre-tax loss is determined through the use of modeling techniques, but such estimate does not represent our total potential loss for such exposures. We seek to limit the probable maximum pre-tax loss to a specific level for severe catastrophic events. Currently, we generally seek to limit the probable maximum pre-tax loss to approximately 25% of total shareholders' equity for a severe catastrophic event in any geographic zone that could be expected to occur once in every 250 years, although we reserve the right to change this threshold at any time. There can be no assurances that we will not suffer pre-tax losses greater than 25% of our total shareholders' equity from
At December 31, 2008, we had access to a $300.0 million unsecured revolving loan and letter of credit facility and a $1.0 billion secured letter of credit facility (the "Credit Agreement"). The $300.0 million unsecured revolving loan is also available for the issuance of unsecured letters of credit up to $100.0 million for Arch Re U.S. Borrowings of revolving loans may be made by ACGL and Arch Re U.S. at a variable rate based on LIBOR or an alternative base rate at our option. Secured letters of credit are available for issuance on behalf of our insurance and reinsurance subsidiaries. Issuance of letters of credit and borrowings under the Credit Agreement are subject to our compliance with certain covenants and conditions, including absence of a material adverse change. These covenants require, among other things, that we maintain a debt to total capital ratio of not greater than 0.35 to 1 and shareholders' equity in excess of $1.95 billion plus 25% of future aggregate net income for each quarterly period (not including any future net losses) beginning after June 30, 2006 and 25% of future aggregate proceeds from the issuance of common or preferred equity and that our principal insurance and reinsurance subsidiaries maintain at least a "B++" rating from A.M. Best. In addition, certain of our subsidiaries which are party to the Credit Agreement are required to maintain minimum shareholders' equity levels. We were in compliance with all covenants contained in the Credit Agreement at December 31, 2008. The Credit Agreement expires on August 30, 2011.
Including the secured letter of credit portion of the Credit Agreement and another letter of credit facility (together, the "LOC Facilities"), we have access to letter of credit facilities for up to a total of $1.45 billion. The principal purpose of the LOC Facilities is to issue, as required, evergreen standby letters of credit in favor of primary insurance or reinsurance counterparties with which we have entered into reinsurance arrangements to ensure that such counterparties are permitted to take credit for reinsurance obtained from our reinsurance subsidiaries in United States jurisdictions where such subsidiaries are not licensed or otherwise admitted as an insurer, as required under insurance regulations in the United States, and to comply with requirements of Lloyd's of London in connection with qualifying quota share and other arrangements. The amount of letters of credit issued is driven by, among other things, the timing and payment of catastrophe losses, loss development of existing reserves, the payment pattern of such reserves, the further expansion of our business and the loss experience of such business. When issued, certain letters of credit are secured by a portion of our investment portfolio. In addition, the LOC Facilities also require the maintenance of certain covenants, which we were in compliance with at December 31, 2008. At such date, we had approximately $599.9 million in outstanding letters of credit under the LOC Facilities, which were secured by investments totaling $697.6 million. In May 2008, we borrowed $100.0 million under the Credit Agreement at a variable interest rate that is based on 1 month, 3 month or 6 month reset option terms and their corresponding term LIBOR rates plus 27.5 basis points. The proceeds from such borrowings, which are repayable in August 2011, were contributed to Arch Re Bermuda and used to fund the investment in Gulf Re noted below.
(3)As part of our securities lending program, we loan certain fixed income securities to third parties and receive collateral, primarily in the form of cash. The collateral received is reinvested and is reflected as "short-term investment of funds received under securities lending agreements, at market value." Such collateral is due back to the third parties at the close of the securities lending transaction.