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Components of net periodic benefit cost (Tables) | 3 Months Ended
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Mar. 31, 2012
Components of net periodic benefit cost [Abstract] |
Schedule of Net Benefit Costs | Components of net periodic benefit cost
| Pension Benefits |  | Other Postretirement Benefits
| Three months ended March 31, |  | Three months ended March 31,
| 2012 | 2011 |  | 2012 | 2011
Service cost | $ | 895 |  | $ | 858 |  |  | $ | 525 |  | $ | 359 |
Interest cost | 1,830 |  | 1,680 |  |  | 1,486 |  | 1,386 |
Expected return on plan assets | (1,700 | ) | (1,540 | ) |  | — |  | — |
Amortization of prior service cost (1) | 35 |  | 35 |  |  | (1,060 | ) | (15,155 | )
Amortization of net loss | 688 |  | 482 |  |  | 1,496 |  | 5,803 |
Net periodic benefit cost | $ | 1,748 |  | $ | 1,515 |  |  | $ | 2,447 |  | $ | (7,607 | )
(1) | Plan amendments made in November 2010 resulted in a reduction in OPEB liability and a credit to accumulated other comprehensive loss. The resulting prior service benefit and actuarial losses were amortized ratably into income over the period November 1, 2010 to June 30, 2011 at which time the CAWV OPEB plan terminated.

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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 -Topic 715 -SubTopic 20 -Publisher FASB -Number -Article -Subparagraph (h) -Name Accounting Standards Codification -Paragraph 1 -Section 50 -URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920 + Details
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