Restatement of Previously Issued Financial Statements - Condensed Consolidated Statements of Income (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Depreciation, depletion and amortization	$ 23,775,000	$ 16,530,000	$ 59,937,000	$ 42,003,000
Total expenses	50,825,000	25,743,000	113,267,000	96,185,000
Income (loss) from operations	7,912,000	1,140,000	30,014,000	(33,551,000)
Loss before income taxes	(19,992,000)	(12,080,000)	(64,333,000)	(43,576,000)
Income tax benefit	282,000	4,956,000	6,493,000	15,854,000
Net loss	(19,710,000)	(7,124,000)	(57,840,000)	(27,722,000)
Net loss attributable to common stockholders	$ (21,685,000)	$ (8,948,000)	$ (63,636,000)	$ (29,842,000)
Net loss per common share
Basic (in dollars per share)	$ (0.88)	$ (0.41)	$ (2.59)	$ (1.37)
Diluted (in dollars per share)	$ (0.88)	$ (0.41)	$ (2.59)	$ (1.37)
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Depreciation, depletion and amortization		$ 15,929,000		$ 40,623,000
Total expenses		25,142,000		94,805,000
Income (loss) from operations		1,741,000		(32,171,000)
Loss before income taxes		(11,479,000)		(42,196,000)
Income tax benefit		4,718,000		15,339,000
Net loss		(6,761,000)		(26,857,000)
Net loss attributable to common stockholders		$ (8,585,000)		$ (28,977,000)
Net loss per common share
Basic (in dollars per share)		$ (0.39)		$ (1.33)
Diluted (in dollars per share)		$ (0.39)		$ (1.33)
Correction
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Depreciation, depletion and amortization		$ 601,000		$ 1,380,000
Total expenses		601,000		1,380,000
Income (loss) from operations		(601,000)		(1,380,000)
Loss before income taxes		(601,000)		(1,380,000)
Income tax benefit		(238,000)		(515,000)
Net loss		(363,000)		(865,000)
Net loss attributable to common stockholders		$ (363,000)		$ (865,000)
Net loss per common share
Basic (in dollars per share)		$ (0.02)		$ (0.04)
Diluted (in dollars per share)		$ (0.02)		$ (0.04)