and 5.4%, respectively of our investment portfolio, including cash and cash equivalents. As of December 31, 2004, the potential impact of a 10% decline in each of the foreign exchange rates on the valuation of investment assets denominated in those respective foreign currencies would result in a total of $111.6 million decline in the fair value of the total investment portfolio. We frequently review our investment portfolio for declines in value, and focus our attention on securities which have a market value of less than 80% of their amortized cost at the time of review Generally, a change in the market or interest rate environment does not constitute an impairment of an investment but rather a temporary decline. Temporary declines in investments will be recorded as unrealized losses in accumulated other comprehensive income. If we determine that a decline is “other than temporary,” the carrying value of the investment will be written down to the fair value and a realized loss will be recorded in our consolidated statements of operations. Our assessments are based on current evaluations of the financial position and future projections of the entity that issued the investment security Prior assessments can change, depending upon current pertinent information. In determining possible impairment of debt securities held as investments, we review market and industry shifts, debt payment schedules that report how current and timely the issuer is with inter est and principal payments, the issuer’s current financial position, the effect of foreign exchange rates and relevant analysis by rating agencies, investment advisors and analysts. In determining the possible impairment of equity securities, we review market and industry shifts, historical price to earnings ratios, recent financial statements, independent auditor’s reports on the issuer’ financial statements and any significant recommendations by investment advisors or rating agencies. Additional relevant information is also considered in determining the valuation of an investment. The following table reflects our investments’ fair value and gross unr ealized depreciation, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, as of December 31, 2004 (in thousands): Investment Impairment Risk Duration of Unr ealized Loss Less than 12 Months Greater than 12 Months Total Gross Gross Gross Unrealized Number of Unrealized Number of Unrealized Number of Fair Value Depreciation Securities Fair Value Depreciation Securities Fair Value Depreciation Securities Fixed income securities  investment grade: United States government  agencies and authorities $667,309 $(17,214) 16 $511,952 $(32,822) 4 $1,179,261 $(50,036) 20 States, municipalities  and political subdivisions 25,995 (358) 5 10,311 (323) 2 36,306 (681) 7 All other corporate 172,495 (1,501) 2 — — — 172,495 (1,501) 2 Total investment grade 865,799 (19,073) 23 522,263 (33,145) 6 1,388,062 (52,218) 29 Fixed income securities  non-investment grade: States, municipalities and  political subdivisions 4,010 (6,352) 1 — — — 4,010 (6,352) 1 All other corporate 114,267 (14,052) 6 — — — 114,267 (14,052) 6 Total non-investment  grade 118,277 (20,404) 7 — — — 118,277 (20,404) 7 Total fixed income 984,076 (39,477) 30 522,263 (33,145) 6 1,506,339 (72,622) 36 Common stocks,  at fair value 131,520 (34,004) 4 73,767 (11,342) 1 205,287 (45,346) 5 Total temporarily  impaired securities $1,115,596 $(73,481) 34 $596,030 $(44,487) 7 $1,711,626 $(117,968) 41 39