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ACCUMULATED OTHER COMPREHENSIVE LOSS - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |
Other components of net periodic pension and postretirement benefits | $ (408) | $ (333)
Income tax expense | 1,061 | 1,277
Net income | 4,439 | 2,979
Reclassification out of Accumulated Other Comprehensive Income |  |
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |
Net income | (13) | (21)
Defined Benefit and Other Benefit Plans | Reclassification out of Accumulated Other Comprehensive Income |  |
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |
Income tax expense | (5) | (12)
Prior Service Costs | Reclassification out of Accumulated Other Comprehensive Income |  |
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |
Other components of net periodic pension and postretirement benefits | (55) | (55)
Actuarial Losses | Reclassification out of Accumulated Other Comprehensive Income |  |
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |
Other components of net periodic pension and postretirement benefits | $ 73 | $ 88

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