Quarterly report pursuant to Section 13 or 15(d)

Property, Plant and Equipment - Schedule of Depreciation, Amortization, Accretion, and Depletion (Details)

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Property, Plant and Equipment - Schedule of Depreciation, Amortization, Accretion, and Depletion (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Property, Plant and Equipment [Abstract]        
Depreciation expense $ 28,099 $ 27,058 $ 56,165 $ 51,456
Depletion expense 1,734 1,340 1,946 1,427
Amortization expense 284 2,382 568 4,790
Accretion expense 28 15 42 30
Depreciation, depletion, amortization and accretion $ 30,145 $ 30,795 $ 58,721 $ 57,703