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Discontinued Operations and Assets Held For Sale - Schedule of Activity From Discontinued Operations (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Discontinued Operations And Disposal Groups [Abstract]        
Impairments $ (103) $ (226) $ (821) $ (495)
Changes in environmental estimates 30 105 335 2,906
Other operating income   3   11
Earnings (loss) from discontinued operations $ (73) $ (118) $ (486) $ 2,422