Oil and Natural Gas Properties (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Oil And Natural Gas Properties [Line Items]
Impairment of proved and unproved oil and gas properties	$ 0	$ 66,648,000	$ 0	$ 66,648,000
Proved Oil and Natural Gas Properties
Oil And Natural Gas Properties [Line Items]
Depletion expenses	$ 10,700,000	9,900,000	$ 20,300,000	17,700,000
Impairment of proved and unproved oil and gas properties		63,000,000		63,000,000
Unproved Oil and Gas Properties
Oil And Natural Gas Properties [Line Items]
Impairment of proved and unproved oil and gas properties		$ 3,600,000		$ 3,600,000
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