4. Cash, Cash Equivalents and Marketable Securities

Cash equivalents are highly liquid investments that are readily convertible into cash with original maturities of three months or less when purchased. Marketable securities consist of securities with original maturities greater than 90 days when purchased. The Company classifies these marketable securities as available-for-sale and records them at fair value in the accompanying consolidated balance sheets. Unrealized gains or losses are included in accumulated other comprehensive loss. Premiums or discounts from par value are amortized to other income over the life of the underlying security.

Cash equivalents and marketable securities, available-for-sale, consisted of the following at December 31, 2020 and December 31, 2019 (in thousands):

Although available to be sold to meet operating needs or otherwise, securities are generally held through maturity. The cost of securities sold is determined based on the specific identification method for purposes of recording realized gains and losses. During, the years ended December 31, 2020, 2019 and 2018, there were no realized gains or losses on sales of investments, and no investments were adjusted for other than temporary declines in fair value.

There were no marketable securities held as of December 31, 2020 and all marketable securities held at December 31 2019 had maturities of less than twelve months when purchased.