Employee Benefit Plan - Pre-Tax Amounts Recognized as Component of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)
$ in Thousands |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
| DB Pension Plan |
|
|
|
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |
|
|
|
| Net actuarial loss (gain) |
$ 39,960
|
$ 39,601
|
$ 38,695
|
| Prior service cost (credit) |
(30)
|
(40)
|
(55)
|
| Total |
39,930
|
39,561
|
38,640
|
| Actuarial loss |
1,041
|
|
|
| Prior service cost |
(10)
|
|
|
| Total |
1,031
|
|
|
| Life and Healthcare Plan |
|
|
|
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |
|
|
|
| Net actuarial loss (gain) |
1,767
|
1,093
|
889
|
| Prior service cost (credit) |
(668)
|
235
|
250
|
| Total |
1,099
|
1,328
|
1,139
|
| Actuarial loss |
62
|
|
|
| Prior service cost |
(62)
|
|
|
| Total |
0
|
|
|
| SERPs |
|
|
|
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |
|
|
|
| Net actuarial loss (gain) |
9,086
|
7,077
|
6,739
|
| Prior service cost (credit) |
602
|
689
|
576
|
| Total |
9,688
|
$ 7,766
|
$ 7,315
|
| Actuarial loss |
529
|
|
|
| Prior service cost |
87
|
|
|
| Total |
$ 616
|
|
|