. the amortized cost of debt securities classified as available-for-sale is adjusted for amortization of premiums and accretion of discounts to maturity , or in the case of mortgage-backed securities , over the estimated life of the security . such amortization is included in interest income from investments . realized gains and losses , and declines in value judged to be other-than-temporary are included in other income . the cost of securities sold is based on the specific identification method