pre_text: In relation to the oil derivative instrument (see note 24), the fair value was determined using the estimated discounted cash flows of the additional payments due to us as a result of oil prices moving above a contractual oil price floor over the term of the liquefaction tolling agreement ("LTA"). Significant inputs used in the valuation of the oil derivative instrument include management’s estimate of an appropriate discount rate and the length of time to blend the long-term and the short-term oil prices obtained from quoted prices in active markets. The changes in fair value of our oil derivative instrument is recognized in each period in current earnings in "Realized and unrealized gain on oil derivative instrument" as part of the consolidated statement of income. The realized and unrealized (loss)/ gain on the oil derivative instrument is as follows: The unrealized loss/gain results from movement in oil prices above a contractual floor price over term of the LTA; the realized gain results from monthly billings above the base tolling fee under the LTA. For further information on the nature of this derivative, refer to note 24.
table: Year Ended December 31,
table: (in thousands of $) 2019 2018 2017
table: Realized gain on oil derivative instrument 13,089 26,737 —
table: Unrealized (loss)/gain on oil derivative instrument  (39,090) (9,970) 15,100
table: (26,001) 16,767 15,100
question: Analyse this data from a financial earnings document. What was the change in realized gain on oil derivative instrument from 2017 to 2018?