| | | 12/31/2017 ThUS$ | | | 12/31/2016 ThUS$ | | 12/31/2015 ThUS | |
Opening balance | | | (22,532) | | | (21,995) | | (30,952) | |
Current cost of service | | | (934) | | | (1,333) | | (898) | |
Interest cost | | | (1,488) | | | (1,407) | | (1,588) | |
Actuarial gain/loss | | | (1,144) | | | (2,253) | | 1,242 | |
Exchange rate difference | | | (2,284) | | | (1,215) | | 3,582 | |
Benefits paid during the year | | | 937 | | | 5,671 | | 6,619 | |
Balance | | | (27,445) | | | (22,532) | | (21,995) | |