Pension and Other Post-Retirement Benefits (Tables)
 6 Months Ended
Jun. 30, 2018
Retirement Benefits [Abstract]  
Components of Net Periodic Benefit Costs
The following table provides the components of net periodic benefit (credit) costs:
 
For the Three Months Ended June 30,
 
For the Six Months Ended June 30,
 
2018
 
2017
 
2018
 
2017
Components of net periodic pension benefit cost:
 
 
 
 
 
 
 
Service cost
$
8

 
$
8

 
$
17

 
$
17

Interest cost
19

 
20

 
38

 
40

Expected return on plan assets
(24
)
 
(23
)
 
(49
)
 
(47
)
Amortization of actuarial loss
7

 
9

 
14

 
18

Net periodic pension benefit cost
$
10

 
$
14

 
$
20

 
$
28

 
 
 
 
 
 
 
 
Components of net periodic other post-retirement benefit (credit) cost:
 
 
 
 
 
 
 
Service cost
$
2

 
$
2

 
$
5

 
$
5

Interest cost
5

 
6

 
11

 
13

Expected return on plan assets
(6
)
 
(6
)
 
(13
)
 
(13
)
Amortization of prior service credit
(4
)
 
(4
)
 
(9
)
 
(9
)
Amortization of actuarial loss
1

 
2

 
2

 
5

Net periodic other post-retirement benefit (credit) cost
$
(2
)
 
$
—

 
$
(4
)
 
$
1