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, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Property, Plant and Equipment [Abstract]        
Depreciation expense $ 27,058 $ 17,229 $ 51,456 $ 32,196
Depletion expense 1,340 382 1,427 384
Amortization expense 2,382 2,268 4,790 4,536
Accretion expense 15 14 30 14
Depreciation, depletion, amortization and accretion $ 30,795 $ 19,893 57,703 37,130
Depreciation expense for assets under capital leases     $ 400 $ 200