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Employee Benefit Plans - Summary of Defined Benefit Pension Plan and Other Postretirement Defined Benefit Plan (Detail) (USD $)
In Thousands, unless otherwise specified |
3 Months Ended | |
|---|---|---|
|
Mar. 31, 2015
|
Mar. 31, 2014
|
|
| Pension Benefits [Member] | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Service cost | $ 107 | $ 114 |
| Interest cost | 2,938 | 3,335 |
| Recognized actuarial loss (gain) | 170 | 71 |
| Expected return on plan assets | (3,477) | (3,814) |
| Net periodic benefit income | (262) | (294) |
| Other Postretirement Benefits [Member] | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Service cost | 7 | 24 |
| Interest cost | 161 | 225 |
| Recognized actuarial loss (gain) | (283) | (84) |
| Amortization of prior service credits | (2,457) | (2,494) |
| Net periodic benefit income | $ (2,572) | $ (2,329) |