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EMPLOYEE BENEFIT PLANS (Notes) | 3 Months Ended
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Mar. 31, 2015
Employee Benefit Plans [Line Items] |
EMPLOYEE BENEFIT PLANS |
7. | EMPLOYEE BENEFIT PLANS
The following tables set forth the components of net periodic benefit cost for our pension and other postretirement benefit plans for the periods indicated:
| Pension Benefits
| Three Months Ended |  | Three Months Ended
| March 31, |  | March 31,
| 2015 |  | 2014
| (Thousands of dollars)
Components of net periodic benefit cost |  |  |
Service cost | $ | 3,524 |  |  | $ | 2,768 |
Interest cost | 10,652 |  |  | 10,948 |
Expected return on assets | (15,362 | ) |  | (14,965 | )
Amortization of unrecognized prior service cost | 67 |  |  | 137 |
Amortization of net loss | 11,055 |  |  | 7,550 |
Net periodic benefit cost | $ | 9,936 |  |  | $ | 6,438 |
| Other Postretirement Benefits
| Three Months Ended |  | Three Months Ended
| March 31, |  | March 31,
| 2015 |  | 2014
| (Thousands of dollars)
Components of net periodic benefit cost |  |  |
Service cost | $ | 849 |  |  | $ | 1,174 |
Interest cost | 2,666 |  |  | 2,901 |
Expected return on assets | (2,908 | ) |  | (2,848 | )
Amortization of unrecognized prior service cost | (440 | ) |  | (440 | )
Amortization of net loss | 1,510 |  |  | 992 |
Net periodic benefit cost | $ | 1,677 |  |  | $ | 1,779 |
We recover qualified pension benefit plan and other postretirement benefit plan costs through rates charged to our customers. Certain utility commissions require that the recovery of these costs be based on specific guidelines. The difference between these regulatory-based amounts and the periodic benefit cost calculated pursuant to GAAP is deferred as a regulatory asset or liability and amortized to expense over periods in which this difference will be recovered in rates, as promulgated by the applicable utility commission. Regulatory adjustments to the net periodic benefit cost were not material for the three month periods ended March 31, 2015 and 2014.

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- Definition The entire disclosure for pension and other postretirement benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2410-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450702-114947 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6414199&loc=d3e39622-114963 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39675-114964 + Details
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