revenue and expense in major foreign currencies in which we operate, in order to reduce the impact of foreign currency on our results. We also enter into foreign exchange forward contracts and options to reduce the impact of foreign currency on balance sheet items. The effective portion of changes in the fair value of forward exchange contracts and options that are classified as cash flow hedges are recorded in other comprehensive income (loss). We estimate the fair value of such derivative contracts by reference to forward and spot rates quoted in active markets. Establishing and accounting for foreign exchange contracts involve judgments, such as determining the fair value of the contracts, determining the nature of the exposure, assessing its amount and timing, and evaluating the effectiveness of the hedging arrangement. Although we believe that our estimates are accurate and meet the requirement of hedge accounting, if actual results differ from these estimates, such difference could cause fluctuation of our recorded revenue and expenses. Fair Value Measurement of Short-Term Interest-Bearing Investments Our short-term interest-bearing investments are classified as available-for-sale securities and are stated at fair value in our consolidated balance sheets. Unrealized gains or losses are reported as a separate component of accumulated other comprehensive income (loss), net of tax. Such short-term interest-bearing investments consist primarily of money market funds, U.S. government treasuries, corporate bonds and U.S. agency securities. We believe we have conservative investment policy guidelines. Our interest-bearing investments are priced by pricing vendors and are classified as Level 1 or Level 2 investments, since these vendors either provide a quoted market price in an active market or use observable inputs such as quoted market prices for similar instruments, market dealer quotes, market spreads, non-binding market prices that are corroborated by observable market data and other observable market information and discounted cash flow techniques using observable market inputs. For securities with unrealized losses that we intend to sell or it is more likely than not that we will be required to sell the securities before recovery, the entire difference between amortized cost and fair value is recognized in earnings. For securities that we do not intend to sell and it is not more likely than not that we will be required to sell, we used a discounted cash flow analysis to determine the portion of the impairment that relates to credit losses. To the extent that the net present value of the projected cash flows was less than the amortized cost of the security, the difference is considered a credit loss and is recorded through earnings. The inputs on the future performance of the underlying assets used in the cash flow models include prepayments, defaults and loss severity assumptions. The other-than-temporary impairment on our short-term interest-bearing investments was immaterial during fiscal 2013, 2012 and 2011. Given the relative reliability of the inputs we use to value our investment portfolio, and because substantially all of our valuation inputs are obtained using quoted market price in an active market or observable inputs, we do not believe that the nature of estimates and assumptions affected by levels of subjectivity and judgment was material to the valuation of the investment portfolio as of September 30, 2013. It is possible that the valuation of the securities will further fluctuate, and as market conditions change, we may determine that unrealized losses, which are currently considered temporary in nature, may become “other than temporary” resulting in additional impairment charges. Accounts Receivable Reserves The allowance for doubtful accounts is for estimated losses resulting from accounts receivable for which their collection is not reasonably assured. We evaluate accounts receivable to determine if they will ultimately be collected. Significant judgments and estimates are involved in performing this evaluation, which we base on factors that may affect a customer’s ability and intent to pay, such as past experience, credit quality of the customer, age of the receivable balance and current economic conditions. If collection is not reasonably assured at the time the transaction is consummated, we do not recognize revenue until collection becomes reasonably assured. If we estimate that our customers’ ability and intent to make payments have been impaired, additional allowances may be required. We regularly review the allowance for doubtful accounts by considering factors that may affect a customer’s ability to pay, such as historical experience, credit quality, age of the accounts receivable balances, and current economic conditions. 43