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Pension and other post-retirement benefits | 6 Months Ended
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Jun. 30, 2019
Retirement Benefits [Abstract] |
Pension and other post-retirement benefits | Pension and other post-employment benefits The following table lists the components of net benefit costs for the pension plans and other post-employment benefits ("OPEB") in the unaudited interim consolidated statements of operations.
| Pension benefits
| Three Months Ended June 30 |  | Six Months Ended June 30
| 2019 |  | 2018 |  | 2019 |  | 2018
Service cost | $ | 2,795 |  |  | $ | 3,614 |  |  | $ | 6,060 |  |  | $ | 7,228 |
Non-service costs |  |  |  |  |  |  |
Interest cost | 3,670 |  |  | 4,459 |  |  | 8,429 |  |  | 8,390 |
Expected return on plan assets | (3,088 | ) |  | (7,005 | ) |  | (10,211 | ) |  | (14,011 | )
Amortization of net actuarial loss | 2,060 |  |  | 111 |  |  | 1,744 |  |  | 223 |
Amortization of prior service credits | (412 | ) |  | (156 | ) |  | (390 | ) |  | (311 | )
Amortization of regulatory assets/liability | 1,194 |  |  | 3,091 |  |  | 4,271 |  |  | 5,157 |
| 3,424 |  |  | 500 |  |  | 3,843 |  |  | (552 | )
Net benefit cost | $ | 6,219 |  |  | $ | 4,114 |  |  | $ | 9,903 |  |  | $ | 6,676 |
8. | Pension and other post-employment benefits (continued)
| OPEB
| Three Months Ended June 30 |  | Six Months Ended June 30
| 2019 |  | 2018 |  | 2019 |  | 2018
Service cost | $ | 1,203 |  |  | $ | 1,487 |  |  | $ | 2,402 |  |  | $ | 2,974 |
Non-service costs |  |  |  |  |  |  |
Interest cost | 1,834 |  |  | 1,625 |  |  | 3,618 |  |  | 3,251 |
Expected return on plan assets | (1,371 | ) |  | (1,849 | ) |  | (3,301 | ) |  | (3,697 | )
Amortization of net actuarial gain | (424 | ) |  | (38 | ) |  | (476 | ) |  | (77 | )
Amortization of prior service credits | (10 | ) |  | (65 | ) |  | (105 | ) |  | (131 | )
Amortization of regulatory assets/liability | 294 |  |  | 347 |  |  | 1,461 |  |  | 1,534 |
| 323 |  |  | 20 |  |  | 1,197 |  |  | 880 |
Net benefit cost | $ | 1,526 |  |  | $ | 1,507 |  |  | $ | 3,599 |  |  | $ | 3,854 |
The service cost components of pension plans and OPEB are shown as part of operating expenses within operating income in the unaudited interim consolidated statements of operations. The remaining components of net benefit costs are considered non-service costs and have been included outside of operating income in pension and post-employment non-service costs in the unaudited interim consolidated statements of operations.

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- References No definition available. + Details
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- Definition The entire disclosure for pension and other postretirement benefits. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -URI http://asc.fasb.org/topic&trid=2235017 + Details
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