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Discontinued Operations and Assets Held For Sale - Schedule of Activity From Discontinued Operations (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Discontinued Operations And Disposal Groups [Abstract]        
Impairments $ (329)   $ (718) $ (269)
Changes in environmental estimates 46 $ 551 305 2,804
Other operating income   4   7
Earnings (loss) from discontinued operations $ (283) $ 555 $ (413) $ 2,542