pre_text: GasLog Ltd. and its Subsidiaries
  Notes to the consolidated financial statements (Continued)
  For the years ended December 31, 2017, 2018 and 2019
  (All amounts expressed in thousands of U.S. Dollars, except share and per share data) 26. Derivative Financial Instruments The fair value of the derivative assets is as follows:
table: As of December 31,
table: 2018 2019
table: Derivative assets carried at fair value through profit or loss (FVTPL)
table: Interest rate swaps 15,188 18
table: Forward foreign exchange contracts — 389
table: Derivative assets designated and effective as hedging instruments carried at fair value
table: Cross currency swaps — 3,594
table: Total 15,188 4,001
table: Derivative financial instruments, current assets 6,222 429
table: Derivative financial instruments, non-current assets 8,966 3,572
table: Total 15,188 4,001
question: Analyse this data from a financial earnings document. What was the change in fair value of interest rate swaps from 2018 to 2019?