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Components of net periodic benefit cost | 3 Months Ended
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Mar. 31, 2014
Components of net periodic benefit cost [Abstract] |
Components of net periodic benefit cost | Components of net periodic benefit cost
| Pension Benefits
| Three months ended March 31,
| 2014 | 2013
Service cost | $ | 1,587 |  | $ | 680 |
Interest cost | 2,640 |  | 1,635 |
Expected return on plan assets | (3,397 | ) | (1,720 | )
Amortization of prior service costs | 9 |  | 32 |
Amortization of net loss | 787 |  | 849 |
Net periodic benefit cost | $ | 1,626 |  | $ | 1,476 |
| Other Postretirement Benefits ("OPEB")
| Three months ended March 31,
| 2014 | 2013
Service cost | $ | 677 |  | $ | 493 |
Interest cost | 1,511 |  | 1,323 |
Amortization of prior service cost | (961 | ) | (1,060 | )
Amortization of net loss | 1,024 |  | 1,503 |
Net periodic benefit cost | $ | 2,251 |  | $ | 2,259 |
Employer contributions During the three months ended March 31, 2014, we made contributions of approximately $549 to the qualified defined benefit plans we sponsor.

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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 -URI http://asc.fasb.org/topic&trid=2235017 + Details
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