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Employee Benefit Plans Employee Benefit Plans 4 (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Pension Benefits |  |  |
Components of Net Periodic Benefits Cost: |  |  |
Service cost | $ 5,342 | $ 4,999 | $ 5,094
Interest cost | 7,646 | 7,904 | 7,910
Expected return on plan assets | (11,172) | (9,705) | (9,838)
Amortization of prior service cost (credit) | 0 | 0 | 49
Amortization of actuarial (gain) loss | 1,254 | 923 | 911
Net periodic pension cost under accounting standards | 3,070 | 4,121 | 4,126
Regulatory adjustment | 0 | (465) | (859)
Total expense recognized, before surcharges and allocation to overhead pool | $ 3,070 | $ 4,586 | $ 4,985
Weighted-average assumptions used to determine net periodic cost: |  |  |
Discount rate | 3.76% | 4.44% | 4.65%
Expected long-term return on plan assets | 6.50% | 6.50% | 7.00%
Expected long-term return on plan assets | 6.50% | 6.50% | 7.00%
Post-Retirement Medical Benefits |  |  |
Components of Net Periodic Benefits Cost: |  |  |
Service cost | $ 218 | $ 227 | $ 247
Interest cost | 292 | 324 | 371
Expected return on plan assets | (493) | (466) | (489)
Amortization of prior service cost (credit) | 0 | 0 | (34)
Amortization of actuarial (gain) loss | (769) | (775) | (701)
Net periodic pension cost under accounting standards | (752) | (690) | (606)
Regulatory adjustment | 0 | 0 | 0
Total expense recognized, before surcharges and allocation to overhead pool | $ (752) | $ (690) | $ (606)
Weighted-average assumptions used to determine net periodic cost: |  |  |
Discount rate | 3.52% | 3.97% | 4.25%
Union plan |  |  |
Weighted-average assumptions used to determine net periodic cost: |  |  |
Expected long-term return on plan assets | 6.00% | 6.00% | 7.00%
Expected long-term return on plan assets | 6.00% | 6.00% | 7.00%
Non-union plan |  |  |
Weighted-average assumptions used to determine net periodic cost: |  |  |
Expected long-term return on plan assets | 4.20% | 4.20% | 4.20%
Expected long-term return on plan assets | 4.20% | 4.20% | 4.20%
Minimum | Pension Benefits |  |  |
Weighted-average assumptions used to determine net periodic cost: |  |  |
Rate of compensation increase | 3.00% | 3.00% |
Maximum | Pension Benefits |  |  |
Weighted-average assumptions used to determine net periodic cost: |  |  |
Rate of compensation increase | 8.00% | 8.00% |

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- Definition The total amount of net periodic benefit cost for defined benefit plans during the period, before allocation to overhead pool. + References No definition available. + Details
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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(5) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of net periodic benefit cost (credit) for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition The increase (decrease) during the reporting period in the value of other assets that are created when regulatory agencies permits public utilities to defer costs to the balance sheet. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
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