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Subsequent Events - Additional Information (Detail)				12 Months Ended
	Feb. 02, 2016 USD ($) $ / shares shares	Mar. 09, 2015 USD ($) $ / shares shares	Dec. 09, 2013 $ / shares shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Feb. 23, 2016 USD ($)	Feb. 22, 2016 USD ($)	Feb. 18, 2016 MBbls $ / bbl
Subsequent Event [Line Items]
Shares issued, price per share (in usd per share) | $ / shares		$ 12.80	$ 44.94
Proceeds from sale of common stock | $		$ 462,800,000		$ 462,833,000	$ 0	$ 314,580,000
Unsecured debt | Line of credit | Consent Notes
Subsequent Event [Line Items]
Current borrowing base | $				$ 1,525,000,000.0
Common stock
Subsequent Event [Line Items]
Issuance of common stock, shares | shares		36,800,000	7,000,000
Common stock | Underwriters' option
Subsequent Event [Line Items]
Issuance of common stock, shares | shares		4,800,000
Subsequent event
Subsequent Event [Line Items]
Weighted average floor price (in dollars per barrel) | $ / bbl									41.58
Shares issued, price per share (in usd per share) | $ / shares	$ 4.685
Proceeds from sale of common stock | $	$ 182,900,000
Subsequent event | Unsecured debt | Line of credit | Consent Notes
Subsequent Event [Line Items]
Current borrowing base | $							$ 1,150,000,000.0	$ 1,525,000,000.0
Subsequent event | Common stock
Subsequent Event [Line Items]
Issuance of common stock, shares | shares	39,100,000
Subsequent event | Common stock | Underwriters' option
Subsequent Event [Line Items]
Issuance of common stock, shares | shares	5,100,000
Subsequent event | 2016 Swaps | Not designated as hedging instrument
Subsequent Event [Line Items]
Total notional amount of oil barrels | MBbls									1,131
Subsequent event | 2017 Swaps | Not designated as hedging instrument
Subsequent Event [Line Items]
Total notional amount of oil barrels | MBbls									2,159
Subsequent event | 2018 Swaps | Not designated as hedging instrument
Subsequent Event [Line Items]
Total notional amount of oil barrels | MBbls									186,000

X

- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Average fixed price related to the group of price risk swap derivatives.

+ References

No definition available.

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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The cash inflow from the additional capital contribution to the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3255-108585

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- Definition

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+ References

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- Definition

Number of new stock issued during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 29, 30
-Article 5

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- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

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