Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in oil and natural gas revenues	$ (185,022)
Restricted cash	$ 25,753	$ 14,604	$ 5,977
Discount rate, present value of future revenue	10.00%
Impairment charges	$ 0	0
Capitalized general and administrative costs	7,300	5,600
Interest costs capitalized	1,900	1,200
Accounting Standards Update 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted cash	6,000	$ 1,300
Calculated under Revenue Guidance in Effect before Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in oil and natural gas revenues	(2,200)
Decrease in production taxes, transportation and processing expenses	$ 2,200