(6)   Investments in Available-for-Sale Securities and Other Cost Investments

All marketable equity and debt securities held by the Company are classified as available-for-sale ("AFS") and are carried at fair value generally based on quoted market prices. GAAP permits entities to choose to measure many financial instruments, such as AFS securities, and certain other items at fair value and to recognize the changes in fair value of such instruments in the entity's statement of operations. The Company previously had entered into economic hedges for certain of its non-strategic AFS securities (although such instruments were not accounted for as fair value hedges by the Company). Changes in the fair value of those economic hedges were reflected in the Company's statement of operations as unrealized gains (losses). In order to better match the changes in fair value of the subject AFS securities and the changes in fair value of the corresponding economic hedges in the Company's financial statements, the Company has elected to account for those of its AFS securities which it considers to be non-strategic ("Fair Value Option Securities") at fair value. Accordingly, changes in the fair value of Fair Value Option Securities, as determined by quoted market prices, are reported in realized and unrealized gains (losses) on financial instruments in the accompanying consolidated statements of operations.

Investments in AFS securities, including Fair Value Option Securities separately aggregated, and other cost investments are summarized as follows:

Unrealized Holding Gains and Losses

There were no unrealized holding gains or losses related to investments in AFS securities at December 31, 2015 or 2014.