(in thousands of USD) | December 31, 2017 | December 31, 2016 | December 31, 2015 | |||||||||||||||||
EUR | USD | EUR | USD | EUR | USD | |||||||||||||||
Trade payables | (7,891 | ) | (11,383 | ) | (8,725 | ) | (9,383 | ) | (9,913 | ) | (13,121 | ) | ||||||||
Operating expenses | (89,289 | ) | (452,113 | ) | (92,608 | ) | (440,830 | ) | (89,457 | ) | (425,806 | ) | ||||||||
Treasury Notes | (50,010 | ) | — | — | — | — | — | — | — |