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Components of net periodic benefit cost
 3 Months Ended
Mar. 31, 2013
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,
 

2013
2012
Service cost
 
$
680

$
895

Interest cost
 
1,635

1,830

Expected return on plan assets
 
(1,720
)
(1,700
)
Amortization of prior service cost
 
32

35

Amortization of net loss
 
849

688

Net periodic benefit cost
 
$
1,476

$
1,748

 
Other Postretirement Benefits ("OPEB")
 
 
Three months ended March 31,
 
 
2013
2012
Service cost
 
$
493

$
525

Interest cost
 
1,323

1,486

Amortization of prior service cost
 
(1,060
)
(1,060
)
Amortization of net loss
 
1,503

1,496

Net periodic benefit cost
 
$
2,259

$
2,447



Employer contributions
During the three months ended March 31, 2013, we have made contributions of approximately $569 to the qualified defined benefit plans we sponsor.