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Interim Pension and Other Postretirement Benefits (Table) | 9 Months Ended
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Jun. 30, 2017
General Discussion of Pension and Other Postretirement Benefits [Abstract] |
Components of net periodic pension cost table | The components of our net periodic pension cost for our pension and other postretirement benefit plans for the three and nine months ended June 30, 2017 and 2016 are presented in the following table. Most of these costs are recoverable through our tariff rates; however, a portion of these costs is capitalized into our rate base. The remaining costs are recorded as a component of operation and maintenance expense.
| Three Months Ended June 30
| Pension Benefits |  | Other Benefits
| 2017 |  | 2016 |  | 2017 |  | 2016
| (In thousands)
Components of net periodic pension cost: |  |  |  |  |  |  |
Service cost | $ | 5,216 |  |  | $ | 4,698 |  |  | $ | 3,109 |  |  | $ | 2,705 |
Interest cost | 6,296 |  |  | 7,095 |  |  | 2,669 |  |  | 3,106 |
Expected return on assets | (6,993 | ) |  | (6,881 | ) |  | (1,796 | ) |  | (1,566 | )
Amortization of transition obligation | — |  |  | — |  |  | — |  |  | 21 |
Amortization of prior service credit | (57 | ) |  | (57 | ) |  | (411 | ) |  | (411 | )
Amortization of actuarial (gain) loss | 4,248 |  |  | 3,319 |  |  | (706 | ) |  | (541 | )
Net periodic pension cost | $ | 8,710 |  |  | $ | 8,174 |  |  | $ | 2,865 |  |  | $ | 3,314 |
| Nine Months Ended June 30
| Pension Benefits |  | Other Benefits
| 2017 |  | 2016 |  | 2017 |  | 2016
| (In thousands)
Components of net periodic pension cost: |  |  |  |  |  |  |
Service cost | $ | 15,649 |  |  | $ | 14,093 |  |  | $ | 9,327 |  |  | $ | 8,117 |
Interest cost | 18,890 |  |  | 21,284 |  |  | 8,009 |  |  | 9,318 |
Expected return on assets | (20,981 | ) |  | (20,642 | ) |  | (5,389 | ) |  | (4,698 | )
Amortization of transition obligation | — |  |  | — |  |  | — |  |  | 62 |
Amortization of prior service credit | (173 | ) |  | (170 | ) |  | (1,233 | ) |  | (1,233 | )
Amortization of actuarial (gain) loss | 12,746 |  |  | 9,959 |  |  | (2,120 | ) |  | (1,625 | )
Net periodic pension cost | $ | 26,131 |  |  | $ | 24,524 |  |  | $ | 8,594 |  |  | $ | 9,941 |
Schedule of assumptions used table text block | The assumptions used to develop our net periodic pension cost for the three and nine months ended June 30, 2017 and 2016 are as follows:
|  | Pension Benefits |  | Other Benefits
|  | 2017 |  | 2016 |  | 2017 |  | 2016
Discount rate |  | 3.73% |  | 4.55% |  | 3.73% |  | 4.55%
Rate of compensation increase |  | 3.50% |  | 3.50% |  | N/A |  | N/A
Expected return on plan assets |  | 7.00% |  | 7.00% |  | 4.45% |  | 4.45%

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- Definition Tabular disclosure of the assumptions used to determine for pension plans and/or other employee benefit plans the benefit obligation and net benefit cost, including assumed discount rates, rate increase in compensation increase, and expected long-term rates of return on plan assets. + 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) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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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://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=65897934&loc=d3e1928-114920 + Details
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