Debt - Senior Secured Credit Facility (Details) - Secured Debt	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Line of Credit
Debt Instrument [Line Items]
Collateral as a percentage of present value of proved reserves	80.00%
Current ratio requirement (not less than)	1.00
Consolidated interest coverage ratio (not less than)	2.50
Line of Credit
Debt Instrument [Line Items]
Borrowing capacity	$ 2,000,000,000.0
Current borrowing capacity	815,000,000
Line of credit	$ 70,000,000
Interest rate (as a percent)	2.31%
Letters of credit
Debt Instrument [Line Items]
Borrowing capacity	$ 20,000,000
Letters of credit outstanding	$ 0	$ 0
Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	0.50%
Minimum | Senior Secured Credit Facility
Debt Instrument [Line Items]
Commitment fee on unused capacity (as a percent)	0.375%
Minimum | Senior Secured Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.50%
Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.50%
Maximum | Senior Secured Credit Facility
Debt Instrument [Line Items]
Commitment fee on unused capacity (as a percent)	0.50%
Maximum | Senior Secured Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	2.50%