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Employee benefit plans | 3 Months Ended
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Mar. 31, 2012
Employee Benefit Plans [Abstract] |
Pension and Other Postretirement Benefits Disclosure | Employee benefit plans The Company has noncontributory defined benefit pension plans and other postretirement benefit plans for certain eligible employees. Components of net periodic benefit cost for the Company's pension and other postretirement benefit plans were as follows:
Three Months Ended March 31, | Pension Benefits | Other Postretirement Benefits
2012 |  | 2011 |  | 2012 |  | 2011 |
| (In thousands)
Components of net periodic benefit cost: |  |  |  |
Service cost | $ | 345 |  | $ | 827 |  | $ | 412 |  | $ | 339 |
Interest cost | 4,554 |  | 4,960 |  | 1,143 |  | 1,189 |
Expected return on assets | (5,886 | ) | (5,700 | ) | (1,244 | ) | (1,218 | )
Amortization of prior service cost (credit) | (21 | ) | 43 |  | (272 | ) | (669 | )
Amortization of net actuarial loss | 1,681 |  | 1,543 |  | 526 |  | 311 |
Amortization of net transition obligation | — |  | — |  | 532 |  | 531 |
Net periodic benefit cost, including amount capitalized | 673 |  | 1,673 |  | 1,097 |  | 483 |
Less amount capitalized | 234 |  | 248 |  | 138 |  | (67 | )
Net periodic benefit cost | $ | 439 |  | $ | 1,425 |  | $ | 959 |  | $ | 550 |
Defined pension plan benefits to all nonunion and certain union employees hired after December 31, 2005, were discontinued. Employees that would have been eligible for defined pension plan benefits are eligible to receive additional defined contribution plan benefits. Effective January 1, 2010, all benefit and service accruals for nonunion and certain union plans were frozen. Effective June 30, 2011, all benefit and service accruals for an additional union plan were frozen. These employees will be eligible to receive additional defined contribution plan benefits. In addition to the qualified plan defined pension benefits reflected in the table, the Company has an unfunded, nonqualified benefit plan for executive officers and certain key management employees that generally provides for defined benefit payments at age 65 following the employee's retirement or to their beneficiaries upon death for a 15-year period. The Company's net periodic benefit cost for this plan for the three months ended March 31, 2012 and 2011, was $2.1 million and $2.1 million, respectively.

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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 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 87 -Paragraph 264 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. 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