Investments	12 Months Ended
Dec. 31, 2017
Investments
Investments	7. Investments As of December 31, 2017, our investments consisted of U.S. Treasury securities, maturing at various dates through January 2019. As of December 31, 2016 our investments consisted of certificates of deposit with various financial institutions maturing in November 2017. Investments are classified as short- or long-term investments on our consolidated balance sheets based on maturity. U.S Treasury securities are classified as available-for-sale and are recorded at fair value. Certificates of deposits were classified as held-to-maturity and were recorded at amortized cost, which approximated fair value. As of December 31, 2017, all five of our U.S. Treasury securities were in an unrealized loss position, none of which had been in an unrealized loss position for 12 months or greater. Total amortized cost and fair value were $24.9 million and $24.8 million as of December 31, 2017, respectively, with a combined unrealized loss of $0.1 million. Based on review of these securities, we believe that the cost basis of these available-for-sale securities is recoverable and that there were no other-than-temporary impairments on these securities as of December 31, 2017.

7. Investments

As of December 31, 2017, our investments consisted of U.S. Treasury securities, maturing at various dates through January 2019. As of December 31, 2016 our investments consisted of certificates of deposit with various financial institutions maturing in November 2017. Investments are classified as short- or long-term investments on our consolidated balance sheets based on maturity. U.S Treasury securities are classified as available-for-sale and are recorded at fair value. Certificates of deposits were classified as held-to-maturity and were recorded at amortized cost, which approximated fair value.

As of December 31, 2017, all five of our U.S. Treasury securities were in an unrealized loss position, none of which had been in an unrealized loss position for 12 months or greater. Total amortized cost and fair value were $24.9 million and $24.8 million as of December 31, 2017, respectively, with a combined unrealized loss of $0.1 million. Based on review of these securities, we believe that the cost basis of these available-for-sale securities is recoverable and that there were no other-than-temporary impairments on these securities as of December 31, 2017.