Pension Benefits and Other Postretirement Benefit Plans (Tables)
 3 Months Ended
Mar. 31, 2015
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]  
Components of net periodic benefit cost
The components of net periodic benefit cost (income) for the periods indicated are:
(Dollars in thousands)
Pension Benefits
 
Retirement Health and Life Insurance Benefits
Quarter Ended
 
Quarter Ended
Change in benefit obligation:
March 31, 2015
 
March 31, 2014
 
March 31, 2015
 
March 31, 2014
Service cost
$
—

 
$
—

 
$
150

 
$
160

Interest cost
1,839

 
2,018

 
75

 
83

Expected return on plan assets
(2,771
)
 
(3,227
)
 
—

 
—

Amortization of prior service cost
—

 
—

 
—

 
—

Amortization of net loss
413

 
183

 
—

 
31

Settlement charge
—

 
110

 
—

 
—

Net periodic benefit cost (income)
$
(519
)
 
$
(916
)
 
$
225

 
$
274