| | 2017 | | 2016 | | 2015 | | |||
PBO as at January 1 | | $ | 462,554 | | | 447,099 | | | 405,703 | |
Benefits paid by the plan | | | (32,940) | | | (26,031) | | | (25,244) | |
Service cost | | | 28,968 | | | 29,604 | | | 26,836 | |
Interest cost | | | 40,170 | | | 34,857 | | | 31,603 | |
Actuarial (gains) losses recognized in other comprehensive income | | | 13,458 | | | (24,827) | | | 8,201 | |
Past service cost plan amendments | | | - | | | 1,852 | | | - | |
PBO as at December 31 | | $ | 512,210 | | | 462,554 | | | 447,099 | |