Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) Customer	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Joint interest and other receivables	$ 167,573,000	$ 211,308,000
Held-to-maturity securities unrecognized holding gains	0	0
Held-to-maturity securities unrecognized holding losses	0	0
OTTI in debt securities	0	0
Dry hole costs	213,500,000	188,000,000	$ 165,500,000
Upper limit of individual leasehold	1,000,000
Lower limit of individual leasehold	$ 1,000,000
New Accounting Pronouncement Early Adoption Effect
Summary Of Significant Accounting Policies [Line Items]
Reclassification of unamortized debt issuance costs		32,900,000
Sales revenue, net | Customer concentration risk
Summary Of Significant Accounting Policies [Line Items]
Number of customers | Customer	1
Concentration risk, percentage	96.50%
7.75% second lien notes due 2023
Summary Of Significant Accounting Policies [Line Items]
Debt instrument maturity year	2023
Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated economic lives	3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated economic lives	10 years
Proved oil and natural gas properties
Summary Of Significant Accounting Policies [Line Items]
Impairment charges		256,800,000
Unproved oil and natural gas properties
Summary Of Significant Accounting Policies [Line Items]
Impairment charges	$ 66,600,000	$ 26,900,000	$ 70,500,000
Leases expiration dates, description	These leases have expiration dates ranging from 2017 through 2026.
Angolan | Exploration well costs
Summary Of Significant Accounting Policies [Line Items]
Dry hole costs	$ 1,276,400,000
Impairment charges	353,400,000
Block 21 risk services agreement | Sonangol P&P
Summary Of Significant Accounting Policies [Line Items]
Joint interest and other receivables	$ 159,100,000