Pension and other postretirement benefits Net benefit cost of pension and postretirement benefit plans (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
---|---|---|---|---|
Jun. 28, 2015 |
Jun. 29, 2014 |
Jun. 28, 2015 |
Jun. 29, 2014 |
|
Pension | ||||
Defined Benefit Plan Disclosure [Line Items] | ||||
Service cost | $ 469 | $ 447 | $ 940 | $ 897 |
Interest cost | 4,485 | 4,486 | 8,971 | 8,969 |
Expected return on plan assets | (6,427) | (6,264) | (12,852) | (12,524) |
Net amortization and deferral | 1,528 | 1,070 | 3,058 | 2,141 |
Net benefit expense (income) | 55 | (261) | 117 | (517) |
Other Postretirement Benefits | ||||
Defined Benefit Plan Disclosure [Line Items] | ||||
Service cost | 107 | 138 | 214 | 276 |
Interest cost | 511 | 596 | 1,023 | 1,193 |
Expected return on plan assets | 0 | 0 | 0 | 0 |
Net amortization and deferral | 78 | 27 | 155 | 53 |
Net benefit expense (income) | $ 696 | $ 761 | $ 1,392 | $ 1,522 |