Restatement of Previously Issued Financial Statements - Condensed Consolidated Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss	$ (21,593)	$ (23,715)	$ (38,130)	$ (20,598)
Depreciation, depletion and amortization			36,162	25,472
Deferred taxes			(6,432)	(11,262)
Net cash provided by operating activities			38,751	17,112
As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss			(35,428)	(20,096)
Depreciation, depletion and amortization			35,027	24,693
Deferred taxes			(7,999)	(10,985)
Net cash provided by operating activities			38,751	17,112
Correction
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss			(2,702)	(502)
Depreciation, depletion and amortization			1,135	779
Deferred taxes			1,567	(277)
Net cash provided by operating activities			$ 0	$ 0