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Pension and other post-retirement benefits (Tables) | 6 Months Ended
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Jun. 30, 2019
Retirement Benefits [Abstract] |
Components of Net Benefit Costs For Pension Plans and OPEB Recorded as Part of Administrative Expenses | 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 |

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- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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