4. Short-term investments

The Company classifies its short-term investments as available for sale. Short-term investments comprise highly liquid investments with minimum “A-” rated securities and as at period-end consist of U.S. Treasury and agency bonds and corporate entity commercial paper with maturities of more than three months but less than one year at the date of purchase. Short-term investments as of September 30, 2018 have an average maturity of 0.24 years. The investments are reported at fair value with unrealized gains or losses recorded in the condensed consolidated statements of operations and comprehensive loss. Any differences between the cost and fair value of investments are represented by unrealized gains or losses. The fair value of short-term investments are represented by Level 1 fair value measurements – quoted prices in active markets for identical assets.

The following table represents the Company’s available for sale short-term investments by major security type as of September 30, 2018 and December 31, 2017: