For the year ended December 31, 2014, 71% of our group-wide gross written premiums originated from the U.S. E&S lines market. We also have a specialty admitted insurance business in the United States. We intend to concentrate substantially all of our underwriting in casualty insurance and reinsurance, and for the year ended December 31, 2014, we derived 98% of our group-wide gross written premiums were from casualty insurance and reinsurance. We focus on specialty markets in which our underwriters have particular expertise and where we have long-standing distribution relationships; maintaining a strong balance sheet by maintaining appropriate reserves; monitoring reinsurance recoverables carefully; managing our investment portfolio actively without taking undue risk; using technology to monitor trends in our business; responding rapidly to market opportunities and challenges; and actively managing our capital.
Loss reserve estimates are subject to a high degree of variability due to the inherent uncertainty of ultimate claims settlement values. In recording our best estimate of our reserve for losses and loss adjustment expenses, our Reserve Committee typically selects an amount above the actuarial recommendation due to the inherent variation associated with our reserve estimates and the likelihood that there are unforeseen or under-valued liabilities in the actuarial recommendations. We believe that the insurance that we write is subject to above-average variation in reserve estimates. The Excess and Surplus
Combined Ratio. The combined ratio of the Casualty Reinsurance segment for the year ended December 31, 2013 was 101.5%, comprised of a loss ratio of 68.4% and an expense ratio of 33.1%. This compares to the combined ratio for the same period in the prior year of 108.8%, comprised of a loss ratio of 76.5% and an expense ratio of 32.4%.
For the years ended December 31, 2013 and 2012, the total operating expenses of the Corporate and Other segment were $8.3 million and $7.3 million, respectively. The variance from the prior year principally relates to compensation related expenses resulting from the Company’s improved underwriting profits in 2013.
Of our total cash and invested assets of   $1,217.1 million at December 31, 2013, $158.6 million represents the cash and cash equivalent portion of the portfolio. The majority of the portfolio, $729.9 million, is comprised of fixed maturity and equity securities that are classified as available-for-sale and are carried at fair value with unrealized gains and losses on these securities reported, net of applicable taxes, as a separate component of accumulated comprehensive income or loss. Also included in our investments is $71.5 million of short-term investments, $42.1 million of other invested assets and $17.3 million of fixed maturity securities that are classified as trading and held at the U.S. holding company. Our trading portfolio is carried at fair value with changes to the value reported as net investment income in our consolidated income statement.
The Company recorded $2.5 million and $2.8 million of amortization of intangibles for the years ended December 31, 2013 and 2012, respectively.
Our effective tax rate fluctuates from period to period based on the relative mix of income reported by country and the respective tax rates imposed by each tax jurisdiction. For U.S.-sourced income, our federal income tax expense differs from the amounts computed by applying the U.S. federal statutory income tax rate to income before taxes due primarily to interest income on tax-advantaged state and municipal securities (state and municipal securities represented 10.4% and 18.1% of our available-for-sale securities at December 31, 2013 and 2012, respectively) and dividends received income. For the years ended December 31, 2013 and 2012, our income tax provision was an expense of 12.6% and a benefit of 11.5%, respectively, of income before taxes, as the amount of tax-exempt investment income and the dividends received deduction in 2012 were high relative to the level of U.S. pre-tax income for the year.
On September 24, 2014, we closed on an amendment to the senior revolving credit facility which, among other things, included an increase in the size of the unsecured revolving facility from $62.5 million to $112.5 million and extended the maturity date from June 5, 2016 to September 24, 2019. The amendment also reduced the interest rate applicable to borrowings under the revolver such that the current LIBOR margin dropped from 2.25% to 2.00%. At December 31, 2014, we had drawn $73.3 million on the unsecured revolver.
At December 31, 2014 and December 31, 2013, the ratio of total debt outstanding to total capitalization (defined as total debt plus total shareholders’ equity) was 21.9% and 18.8%, respectively. Having debt as part of our capital structure allows us to generate a higher return on equity and greater book value per share results than we could by using equity capital alone.
In our Excess and Surplus Lines segment, we write a small book of excess property insurance (but we do not write primary property insurance). We use catastrophe modeling software to analyze the risk of severe losses from hurricanes and earthquakes on our exposure. We utilize the model in our risk selection, and pricing, as well as to manage our overall portfolio PML accumulations. A PML is an estimate of the amount we would expect to pay in any one catastrophe event within a given annual probability of occurrence (i.e. a return period or loss exceedance probability). Based upon our modeling, a $45.0 million gross catastrophe loss approximates our 1,000 year PML. In the event of a $45.0 million gross property catastrophe loss to the Company, we estimate our pre-tax cost at approximately $7.0 million, including reinstatement premiums and net retentions. In addition to this retention, we would retain any losses in excess of our reinsurance coverage limits.
common loss occurrence, to provide additional capacity for growth and to support new specialty admitted and program business initiatives. This segment purchases reinsurance for at least 50% of the exposed limits on specialty admitted property casualty business. On a program-by-program basis, the Specialty Admitted Insurance segment:
Cash used in investing activities in 2014 reflects our efforts to enhance the yield in our investment portfolio by investing available cash and cash equivalents into higher yielding fixed maturity securities and bank loan participations. Cash and cash equivalents comprised 5.6% of total cash and invested assets at December 31, 2014. Net cash used in financing activities in 2014 is a result of the $70.0 million dividend to shareholders in 2014. A portion of this dividend was funded by additional borrowings on our unsecured revolving credit facility of  $20.0 million. In addition, we drew down an additional $10.0 million on our unsecured revolving credit facility in December 2014 to provide additional operating flexibility at the holding company.