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Employee Benefits (Tables)
 6 Months Ended
Jun. 30, 2017
Employee Benefits [Abstract]  
Components of Net Periodic Benefit Cost for Postretirement Benefit Plans
The components of net periodic benefit cost for our postretirement benefit plans for the three months and six months ended June 30, 2017 and 2016 were as follows (in thousands):

   
Three Months Ended
June 30,
  
Six Months Ended
June 30,
 
Postretirement benefits
 
2017
  
2016
  
2017
  
2016
 
Service cost
 
$
—
  
$
—
  
$
—
  
$
—
 
Interest cost
  
2
   
3
   
4
   
6
 
Amortization of prior service cost
  
—
   
(14
)
  
—
   
(27
)
Actuarial net loss
  
(271
)
  
115
   
(330
)
  
390
 
Net periodic benefit cost (credit)
 
$
(269
)
 
$
104
  
$
(326
)
 
$
369