Asset Retirement Obligations - Asset Retirement Obligations (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jan. 18, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of period	$ 0
Liability incurred during the period	53,294
Liability settled during the period	(5,327)
Accretion expense	1,118
Balance at end of period	49,085
Business Acquisition [Line Items]
ARO liability	0
Droshky Prospect
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liability settled during the period	$ (5,300)
Business Acquisition [Line Items]
ARO liability		$ 53,300
Other receivables		50,800
Acquired property		$ 2,500