Oil and Natural Gas Properties - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Oil And Natural Gas Properties [Line Items]
Accumulated impairments to proved and unproved oil and natural gas properties	$ 121.1	$ 148.2
Proved Oil and Natural Gas Properties
Oil And Natural Gas Properties [Line Items]
Depletion expenses	$ 47.1	$ 36.4
Unproved Oil and Gas Properties | Minimum
Oil And Natural Gas Properties [Line Items]
Unproved oil and gas lease term	3 years
Unproved Oil and Gas Properties | Maximum
Oil And Natural Gas Properties [Line Items]
Unproved oil and gas lease term	5 years