It also is difficult to estimate appropriate loss reserves for our financial guaranty business because of the nature of  potential losses in this business, which are largely influenced by the particular circumstances surrounding individual troubled  credits, including the availability of loss mitigation.  As a result, our loss reserves are less capable of being evaluated based on  historical assumptions or precedent. See “ Our financial guaranty portfolio has experienced losses as a result of the most recent  economic downturn and is susceptible to further deterioration, which could have a material adverse effect on the capital  adequacy of Radian Guaranty .” In addition, in our financial guaranty reinsurance business, we rely , in part, on information  provided by our ceding customers in order to establish reserves. If this information is incomplete, inaccurate or untimely , our  loss reserves may not be estimated accurately and could require material adjustment in future periods as new or corrected  information becomes available.  Our investment portfolio is one of our primary sources of cash flow to support our operations and claim payments. If we  underestimate our policy liabilities or if we improperly structure our investments to meet those liabilities, we could have  unexpected losses, including losses resulting from the forced liquidation of investments before their maturity . We maintain an  investment policy to manage our investments and those of our insurance subsidiaries that are subject to state insurance laws. In  addition, the Freddie Mac Approval for RMAI requires us to maintain a certain level and specific type of liquid assets at Radian  Guaranty. We may be forced to change our investments or investment policies depending upon regulatory , economic and market  conditions and our existing or anticipated financial condition and operating requirements, including the tax position, of our  business segments.  Our investment objectives may not be achieved. Although our portfolio consists mostly of highly-rated investments and  complies with applicable regulatory requirements, the success of our investment activity is af fected by general economic  conditions, which may adversely af fect the markets for credit and interest-rate-sensitive securities, including the extent and  timing of investor participation in these markets, the level and volatility of interest rates and, consequently , the value of our  fixed-income securities. Volatility or illiquidity in the markets in which we hold positions has reduced the market value of some  of our investments and has caused certain other -than-temporary impairments within our portfolio, which, if this worsens  substantially, could have a material adverse ef fect on our liquidity, financial condition and operating results.  Compared to historical averages, interest rates and investment yields on our investments generally have declined in recent  years, which has reduced the investment income we generate. In addition, we have kept a lar ger portion of our investment  portfolio in shorter maturity investments in order to meet the expected liquidity needs of our operating subsidiaries.  This, in  turn, has further reduced our investment income, as interest rates on short-term investments have been minimal.  We depend on  our investments as a source of revenue and a prolonged period of lower than expected investment yields would have an adverse  impact on our revenues and could potentially adversely af fect our results of operations.  Radian Group serves as the holding company for our insurance subsidiaries and does not have any significant operations  of its own. Radian Group’s principal liquidity demands include funds for: (i) the payment of certain corporate expenses;  (ii) interest payments on our outstanding debt; (iii) repayment of the principal amount of our outstanding debt, which after the  February 15, 2013 repayment of $79.4 million in principal amount of our 2013 Notes, currently includes $54.8 million in  principal amount due in 2015, $195.2 million in principal amount due in June 2017 and $450 million in principal amount of  convertible debt due in November 2017; (iv) potential capital support for our mortgage insurance subsidiaries; (v) potential  payments to the U.S. Department of the  Treasury resulting from the examination of our 2000 through 2007 federal tax returns  by the Internal Revenue Service (“IRS”); and (vi) the payment of dividends on our common stock. Radian Group had  immediately available, directly or through an unregulated direct subsidiary , unrestricted cash and marketable securities of  $375.6 million at December 31, 2012. In light of operating losses in our mortgage insurance business, Radian Group may be required to make additional capital  contributions to Radian Guaranty in order to support Radian Guaranty’ s ability to continue writing mortgage insurance in those  states that impose Statutory RBC Requirements. Radian Group also could be required to provide capital support for our other  mortgage insurance subsidiaries if additional capital is required pursuant to insurance laws and regulations, or by the GSEs or  rating agencies. See “ Losses in our mortgage insurance and financial guaranty businesses have reduced Radian Guaranty’s  statutory surplus and increased Radian Guaranty’s risk-to-capital ratio; additional losses in these businesses, without a  corresponding increase in new capital or capital relief, would further negatively impact this ratio, which could limit Radian  Guaranty’s ability to write new insurance and increase restrictions and requirements placed on Radian Guaranty. ”  76 Radian Group’s sources of liquidity may be insufficient to fund its obligations. Our success depends, in part, on our ability to manage risks in our investment portfolio.