8. Fair Value Measurements

As of September 30, 2016 and December 31, 2015, the carrying value of derivative liabilities, which are measured at fair value on a recurring basis, was $123 thousand and $40 thousand, respectively. Its fair value measurement was based on Level 2 inputs.

As of September 30, 2016, the Company did not have any assets measured at fair value on a recurring basis other than cash and cash equivalents and restricted cash, the fair values of which approximate carrying values due to the short-term nature of these instruments. The fair value of assets and liabilities whose carrying value approximates fair value is determined using Level 2 inputs, with the exception of cash (Level 1).

As of September 30, 2016, the total carrying value and estimated fair value of the Company’s 6.625% Senior Notes due July 15, 2021 (the “2021 Notes”), which are not measured at fair value on a recurring basis, were $220,902 thousand and $201,938 thousand, respectively. As of December 31, 2015, the total carrying value and estimated fair value of the 2021 Notes were $220,375 thousand and $157,500 thousand, respectively. The estimated fair values are based on Level 2 inputs.