Employee Benefit Plans - Schedule of Aggregate Fair Value of Asset and Supplemental Asset Mix (Detail) - USD ($)
$ in Millions |
Dec. 31, 2016 |
Dec. 31, 2015 |
| Combined Master Retirement Trust Asset [Line Items] |
|
|
| CMRT asset value |
$ 637.8
|
$ 648.8
|
| CMRT assets comprised of: |
|
|
| Assets not subject to fair value hierarchy |
30.00%
|
30.00%
|
| Assets subject to fair value hierarchy: |
|
|
| Fair value input |
100.00%
|
100.00%
|
| CMRT asset mix: |
|
|
| Percentage of combined master retirement trust asset mix |
100.00%
|
100.00%
|
| Domestic equities, principally publicly traded |
|
|
| CMRT asset mix: |
|
|
| Percentage of combined master retirement trust asset mix |
31.00%
|
29.00%
|
| International equities, principally publicly traded |
|
|
| CMRT asset mix: |
|
|
| Percentage of combined master retirement trust asset mix |
22.00%
|
22.00%
|
| Fixed income securities, principally publicly traded |
|
|
| CMRT asset mix: |
|
|
| Percentage of combined master retirement trust asset mix |
36.00%
|
38.00%
|
| Privately managed limited partnerships |
|
|
| CMRT asset mix: |
|
|
| Percentage of combined master retirement trust asset mix |
5.00%
|
5.00%
|
| Hedge funds |
|
|
| CMRT asset mix: |
|
|
| Percentage of combined master retirement trust asset mix |
5.00%
|
5.00%
|
| Other, primarily cash |
|
|
| CMRT asset mix: |
|
|
| Percentage of combined master retirement trust asset mix |
1.00%
|
1.00%
|
| Level 1 |
|
|
| Assets subject to fair value hierarchy: |
|
|
| Fair value input |
54.00%
|
54.00%
|
| Level 2 |
|
|
| Assets subject to fair value hierarchy: |
|
|
| Fair value input |
8.00%
|
7.00%
|
| Level 3 |
|
|
| Assets subject to fair value hierarchy: |
|
|
| Fair value input |
8.00%
|
9.00%
|