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Benefit plans (Tables)
 3 Months Ended
Mar. 31, 2012
Benefit plans [Abstract]  
Components of net periodic benefit cost
The following table provides the components of net periodic benefit cost for the pension, supplemental executive retirement and other postretirement benefit plans:

 
Three Months Ended March 31,
 
 
Pension and Supplemental
 
 
Other Postretirement
 
 
Executive Retirement Plans
 
 
Benefits
 
 
 
 
 
2012
 
 
2011
 
 
2012
 
 
2011
 
 
(In thousands)
 
 
 
 
 
 
 
 
 
 
 
 
 
Service cost
 
$
2,390
 
 
$
2,172
 
 
$
309
 
 
$
254
 
Interest cost
 
 
4,106
 
 
 
4,122
 
 
 
292
 
 
 
354
 
Expected return on plan assets
 
 
(4,516
)
 
 
(4,194
)
 
 
(790
)
 
 
(823
)
Recognized net actuarial loss
 
 
1,478
 
 
 
1,217
 
 
 
210
 
 
 
187
 
Amortization of prior service cost
 
 
161
 
 
 
162
 
 
 
(1,554
)
 
 
(1,554
)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net periodic benefit cost
 
$
3,619
 
 
$
3,479
 
 
$
(1,533
)
 
$
(1,582
)