Chord Energy (CHRD) 10-Q 7 Nov 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Nov. 04, 2013
Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	30-Sep-13	'
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'Q3	'
Trading Symbol	'OAS	'
Entity Registrant Name	'Oasis Petroleum Inc.	'
Entity Central Index Key	'0001486159	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	93,701,254

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheet (Unaudited) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
ASSETS	'	'
Cash and cash equivalents	$125,440	$213,447
Restricted cash	986,210	0
Short-term investments	0	25,891
Accounts receivable — oil and gas revenues	155,068	110,341
Accounts receivable — joint interest partners	120,058	99,194
Inventory	18,358	20,707
Prepaid expenses	7,440	1,770
Advances to joint interest partners	1,170	1,985
Derivative instruments	374	19,016
Deferred income taxes	8,683	0
Other current assets	473	335
Total current assets	1,423,274	492,686
Property, plant and equipment	'	'
Oil and gas properties (successful efforts method)	3,044,515	2,348,128
Other property and equipment	157,926	49,732
Less: accumulated depreciation, depletion, amortization and impairment	-589,173	-391,260
Total property, plant and equipment, net	2,613,268	2,006,600
Derivative instruments	3,405	4,981
Deferred costs and other assets	43,436	24,527
Total assets	4,083,383	2,528,794
LIABILITIES AND STOCKHOLDERS’ EQUITY	'	'
Accounts payable	39,468	12,491
Advances from joint interest partners	13,211	21,176
Revenues and production taxes payable	133,083	71,553
Accrued liabilities	198,493	189,863
Accrued interest payable	22,873	30,096
Derivative instruments	17,060	1,048
Deferred income taxes	0	4,558
Total current liabilities	424,188	330,785
Long-term debt	2,360,000	1,200,000
Asset retirement obligations	26,999	22,956
Derivative instruments	852	380
Deferred income taxes	293,156	177,671
Other liabilities	2,310	1,997
Total liabilities	3,107,505	1,733,789
Commitments and contingencies (Note 13)	'	'
Stockholders’ equity	'	'
Common stock, $0.01 par value; 300,000,000 shares authorized; 93,854,867 issued and 93,690,494 outstanding at September 30, 2013; 93,432,712 issued and 93,303,298 outstanding at December 31, 2012	926	925
Treasury stock, at cost; 164,373 and 129,414 shares at September 30, 2013 and December 31, 2012, respectively	-5,220	-3,796
Additional paid-in-capital	666,770	657,943
Retained earnings	313,402	139,933
Total stockholders’ equity	975,878	795,005
Total liabilities and stockholders’ equity	$4,083,383	$2,528,794

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheet (Unaudited) (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]	'	'
Common stock, par value (in dollars per share)	$0.01	$0.01
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	93,854,867	93,432,712
Common stock, shares outstanding	93,690,494	93,303,298
Treasury stock, shares	164,373	129,414

Condensed_Consolidated_Stateme

Condensed Consolidated Statement of Operations (Unaudited) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues	'	'	'	'
Oil and gas revenues	$286,952	$178,748	$770,445	$461,857
Well services and midstream revenues	18,546	5,963	37,939	10,484
Total revenues	305,498	184,711	808,384	472,341
Expenses	'	'	'	'
Lease operating expenses	21,831	16,134	59,586	37,979
Well services and midstream operating expenses	10,319	5,420	19,877	7,104
Marketing, transportation and gathering expenses	5,688	2,744	19,856	7,283
Production taxes	26,823	16,433	70,309	43,419
Depreciation, depletion and amortization	72,728	57,684	205,779	140,783
Exploration expenses	463	336	2,712	3,171
Impairment of oil and gas properties	56	36	762	2,607
General and administrative expenses	16,728	13,886	47,238	39,622
Total expenses	154,636	112,673	426,119	281,968
Operating income (loss)	150,862	72,038	382,265	190,373
Other income (expense)	'	'	'	'
Net gain (loss) on derivative instruments	-39,817	-22,441	-41,838	33,568
Interest expense, net of capitalized interest	-22,854	-20,979	-65,429	-48,952
Other income	23	1,147	1,097	2,521
Total other income (expense)	-62,648	-42,273	-106,170	-12,863
Income before income taxes	88,214	29,765	276,095	177,510
Income tax expense	33,715	11,451	102,626	66,712
Net income	$54,499	$18,314	$173,469	$110,798
Earnings per share:	'	'	'	'
Basic (Note 11) (in dollars per share)	$0.59	$0.20	$1.88	$1.20
Diluted (Note 11) (in dollars per share)	$0.59	$0.20	$1.87	$1.20
Weighted average shares outstanding:	'	'	'	'
Basic (Note 11) (in shares)	92,449	92,186	92,408	92,164
Diluted (Note 11) (in shares)	92,836	92,416	92,838	92,343

Condensed_Consolidated_Stateme1

Condensed Consolidated Statement of Changes in Stockholders' Equity (Unaudited) (USD $)	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in-Capital [Member]	Retained Earnings [Member]
In Thousands, unless otherwise specified
Balance at Dec. 31, 2012	$795,005	$925	($3,796)	$657,943	$139,933
Balance, shares at Dec. 31, 2012	'	93,303	129	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'
Stock-based compensation	8,828	1	'	8,827	'
Stock-based compensation, shares	'	422	'	'	'
Treasury stock – tax withholdings	1,424	'	1,424	'	'
Treasury stock - tax withholdings, shares	'	-35	35	'	'
Net income	173,469	'	'	'	173,469
Balance at Sep. 30, 2013	$975,878	$926	($5,220)	$666,770	$313,402
Balance, shares at Sep. 30, 2013	'	93,690	164	'	'

Condensed_Consolidated_Stateme2

Condensed Consolidated Statement of Cash Flows (Unaudited) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:	'	'
Net income	$173,469	$110,798
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Depreciation, depletion and amortization	205,779	140,783
Impairment of oil and gas properties	762	2,607
Deferred income taxes	102,244	66,648
Derivative instruments	41,838	-33,568
Stock-based compensation expenses	8,411	6,627
Debt discount amortization and other	2,693	2,038
Working capital and other changes:	'	'
Change in accounts receivable	-67,487	-69,163
Change in inventory	-8,820	-26,790
Change in prepaid expenses	-5,175	-2,009
Change in other current assets	-138	413
Change in other assets	-63	-119
Change in accounts payable and accrued liabilities	82,246	79,079
Change in other current liabilities	0	4,784
Change in other liabilities	922	0
Net cash provided by operating activities	536,681	282,128
Cash flows from investing activities:	'	'
Capital expenditures	-654,175	-777,516
Acquisition of oil and gas properties	-133,061	0
Increase in restricted cash	-986,210	0
Derivative settlements	-5,135	2,784
Purchases of short-term investments	0	-126,213
Redemptions of short-term investments	25,000	19,994
Advances from joint interest partners	-7,965	17,508
Net cash used in investing activities	-1,761,546	-863,443
Cash flows from financing activities:	'	'
Proceeds from credit facility	160,000	0
Proceeds from issuance of senior notes	1,000,000	400,000
Purchases of treasury stock	-1,424	-1,299
Debt issuance costs	-21,718	-7,955
Net cash provided by financing activities	1,136,858	390,746
Decrease in cash and cash equivalents	-88,007	-190,569
Cash and cash equivalents:	'	'
Beginning of period	213,447	470,872
End of period	125,440	280,303
Supplemental non-cash transactions:	'	'
Change in accrued capital expenditures	10,530	71,572
Change in asset retirement obligations	$4,173	$7,774

Organization_and_Operations_of

Organization and Operations of the Company	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Organization and Operations of the Company	'
	Organization and Operations of the Company
	Organization
	Oasis Petroleum Inc. (together with its subsidiaries, “Oasis” or the “Company”) was formed on February 25, 2010, pursuant to the laws of the State of Delaware, to become a holding company for Oasis Petroleum LLC (“OP LLC”), the Company’s predecessor, which was formed as a Delaware limited liability company on February 26, 2007. In connection with its initial public offering in June 2010 and related corporate reorganization, the Company acquired all of the outstanding membership interests in OP LLC in exchange for shares of the Company’s common stock. In 2007, Oasis Petroleum North America LLC (“OPNA”), a Delaware limited liability company, was formed to conduct domestic oil and natural gas exploration and production activities. In 2008, Oasis Petroleum International LLC (“OPI”), a Delaware limited liability company, was formed to conduct business development activities outside of the United States of America. As of September 30, 2013, OPI had no business activities or material assets. In 2011, the Company formed Oasis Well Services LLC (“OWS”), a Delaware limited liability company, to provide well services to OPNA, and Oasis Petroleum Marketing LLC (“OPM”), a Delaware limited liability company, to provide marketing services to OPNA. In 2013, the Company formed Oasis Midstream Services LLC (“OMS”), a Delaware limited liability company, to provide midstream services to OPNA. As part of the formation of OMS, the Company transferred substantially all of its salt water disposal and other midstream assets from OPNA to OMS.
	Nature of Business
	The Company is an independent exploration and production company focused on the acquisition and development of unconventional oil and natural gas resources in the Williston Basin. The Company’s proved and unproved oil and natural gas properties are located in the Montana and North Dakota areas of the Williston Basin and are owned by OPNA. The Company also operates a marketing business (OPM), a well services business (OWS) and a midstream services business (OMS), all of which are complementary to its primary development and production activities.  Both OWS and OMS are separate reportable business segments.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Summary of Significant Accounting Policies	'
	Summary of Significant Accounting Policies
	Basis of Presentation
	The accompanying condensed consolidated financial statements of the Company include the accounts of Oasis and its wholly owned subsidiaries. The accompanying condensed consolidated financial statements of the Company have not been audited by the Company’s independent registered public accounting firm, except that the Condensed Consolidated Balance Sheet at December 31, 2012 is derived from audited financial statements. All significant intercompany transactions have been eliminated in consolidation. Certain reclassifications of prior year balances have been made to conform such amounts to current year classifications. These reclassifications have no impact on net income. In the opinion of management, all adjustments, consisting of normal recurring adjustments necessary for the fair presentation, have been included. In preparing the accompanying condensed consolidated financial statements, management has made certain estimates and assumptions that affect reported amounts in the condensed consolidated financial statements and disclosures of contingencies. Actual results may differ from those estimates. The results for interim periods are not necessarily indicative of annual results.
	These interim financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain disclosures have been condensed or omitted from these financial statements. Accordingly, they do not include all of the information and notes required by accounting principles generally accepted in the United States of America (“GAAP”) for complete consolidated financial statements and should be read in conjunction with the Company’s audited consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012 (“2012 Annual Report”).
	Significant Accounting Policies
	There have been no material changes to the Company’s critical accounting policies and estimates from those disclosed in the 2012 Annual Report other than those noted below.
	Restricted Cash
	Restricted cash represents aggregate net proceeds from the issuance of $1,000.0 million of 6.875% senior unsecured notes due 2022, which were held in escrow as of September 30, 2013 pending the closing of the acquisition of oil and gas properties in the Company’s West Williston project area (see Note 7 – Long-Term Debt and Note 15 – Subsequent Events). If the acquisition had not closed prior to December 12, 2013, the Company would have been required to use the restricted cash to redeem all of the notes due 2022 at a redemption price equal to 100% of the initial offering price, plus accrued and unpaid interest through the date of redemption.

Inventory

Inventory	9 Months Ended
	Sep. 30, 2013
Inventory Disclosure [Abstract]	'
Inventory	'
	Inventory
	Equipment and materials consist primarily of tubular goods, well equipment to be used in future drilling or repair operations, well fracturing equipment, chemicals and proppant, all of which are stated at the lower of cost or market with cost determined on an average cost method. Crude oil inventories include oil in tank and line fill and are valued at the lower of average cost or market value. Inventory consists of the following:
		September 30,		December 31,
		2013		2012
		(In thousands)
	Equipment and materials	$	12,498	$	16,438
	Crude oil inventory	5,860		4,269
	Total inventory	$	18,358	$	20,707

Property_Plant_and_Equipment

Property, Plant and Equipment	9 Months Ended
	Sep. 30, 2013
Property, Plant and Equipment [Abstract]	'
Property, Plant and Equipment	'
	Property, Plant and Equipment
	The following table sets forth the Company’s property, plant and equipment:
		30-Sep-13			31-Dec-12
		(In thousands)
	Proved oil and gas properties (1)	$	2,916,453		$	2,271,711
	Less: Accumulated depreciation, depletion, amortization and impairment	(568,567		)	(383,564		)
	Proved oil and gas properties, net (2)	2,347,886			1,888,147
	Unproved oil and gas properties	128,062			76,417
	Total oil and gas properties, net	2,475,948			1,964,564
	Other property and equipment	157,926			49,732
	Less: Accumulated depreciation	(20,606		)	(7,696		)
	Other property and equipment, net (2)	137,320			42,036
	Total property, plant and equipment, net	$	2,613,268		$	2,006,600
	__________________
	-1	Included in the Company’s proved oil and gas properties are estimates of future asset retirement costs of $24.0 million and $20.7 million at September 30, 2013 and December 31, 2012, respectively.
	-2	The Company reclassed substantially all of its salt water disposal and other midstream assets from proved oil and gas properties to other property and equipment, effective January 1, 2013.
	As a result of expiring leases and periodic assessments of unproved properties, the Company recorded non-cash impairment charges on its unproved oil and natural gas properties of $56,000 and $0.8 million for the three and nine months ended September 30, 2013, respectively, and $36,000 and $2.6 million for the three and nine months ended September 30, 2012, respectively. No impairment charges on proved oil and natural gas properties were recorded for the three and nine months ended September 30, 2013 or 2012.
	Asset acquisitions. On September 26, 2013, the Company acquired certain oil and natural gas assets totaling approximately 25,000 net acres in its East Nesson project area for cash consideration of $54.8 million, subject to further customary post close adjustments (the “East Nesson Acquisitions”). As part of the East Nesson Acquisitions, the Company also agreed to invest, expend and/or incur expenses of $8.2 million in connection with drilling and completion activities for certain wells (see Note 13 - Commitments and Contingencies). Additionally, the Company paid a deposit of $72.5 million in September 2013 for the acquisition of assets in its West Williston project area (see Note 15 - Subsequent Events), which is included in oil and gas properties on the Company’s Condensed Consolidated Balance Sheet at September 30, 2013.

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	Fair Value Measurements
	In accordance with the Financial Accounting Standards Board’s (“FASB”) authoritative guidance on fair value measurements, the Company’s financial assets and liabilities are measured at fair value on a recurring basis. The Company recognizes its non-financial assets and liabilities, such as asset retirement obligations (“ARO”) and proved oil and natural gas properties upon impairment, at fair value on a non-recurring basis.
	As defined in the authoritative guidance, fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). To estimate fair value, the Company utilizes market data or assumptions that market participants would use in pricing the asset or liability, including assumptions about risk and the risks inherent in the inputs to the valuation technique. These inputs can be readily observable, market corroborated or generally unobservable.
	The authoritative guidance establishes a fair value hierarchy that prioritizes the inputs used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (“Level 1” measurements) and the lowest priority to unobservable inputs (“Level 3” measurements). The three levels of the fair value hierarchy are as follows:
	Level 1 — Unadjusted quoted prices are available in active markets for identical assets or liabilities as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis.
	Level 2 — Pricing inputs, other than unadjusted quoted prices in active markets included in Level 1, are either directly or indirectly observable as of the reporting date. Level 2 includes those financial instruments that are valued using models or other valuation methodologies. These models are primarily industry-standard models that consider various assumptions, including quoted forward prices for commodities, time value, volatility factors and current market and contractual prices for the underlying instruments, as well as other relevant economic measures. Substantially all of these assumptions are observable in the marketplace throughout the full term of the instrument and can be derived from observable data or are supported by observable levels at which transactions are executed in the marketplace.
	Level 3 — Pricing inputs are generally less observable from objective sources, requiring internally developed valuation methodologies that result in management’s best estimate of fair value.
	Financial Assets and Liabilities
	As required, financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement requires judgment and may affect the valuation of fair value assets and liabilities and their placement within the fair value hierarchy levels. The following tables set forth by level within the fair value hierarchy the Company’s financial assets and liabilities that were accounted for at fair value on a recurring basis:
		At fair value as of September 30, 2013
		Level 1		Level 2		Level 3		Total
		(In thousands)
	Assets:
	Money market funds	$	11,274	$	—	$	—	$	11,274
	Commodity derivative instruments (see Note 6)	—		3,779		—		3,779
	Total assets	$	11,274	$	3,779	$	—	$	15,053
	Liabilities:
	Commodity derivative instruments (see Note 6)	$	—	$	17,912	$	—	$	17,912
	Total liabilities	$	—	$	17,912	$	—	$	17,912
		At fair value as of December 31, 2012
		Level 1		Level 2		Level 3		Total
		(In thousands)
	Assets:
	Money market funds	$	66,387	$	—	$	—	$	66,387
	Commodity derivative instruments (see Note 6)	—		23,997		—		23,997
	Total assets	$	66,387	$	23,997	$	—	$	90,384
	Liabilities:
	Commodity derivative instruments (see Note 6)	$	—	$	1,428	$	—	$	1,428
	Total liabilities	$	—	$	1,428	$	—	$	1,428
	The Level 1 instruments presented in the tables above consist of money market funds included in cash and cash equivalents on the Company’s Condensed Consolidated Balance Sheet at September 30, 2013 and December 31, 2012. The Company’s money market funds represent cash equivalents backed by the assets of high-quality major banks and financial institutions. The Company identified the money market funds as Level 1 instruments due to the fact that the money market funds have daily liquidity, quoted prices for the underlying investments can be obtained and there are active markets for the underlying investments.
	The Level 2 instruments presented in the tables above consist of commodity derivative instruments, which include oil collars, swaps and puts. The fair values of the Company’s commodity derivative instruments are based upon a third-party preparer’s calculation using mark-to-market valuation reports provided by the Company’s counterparties for monthly settlement purposes to determine the valuation of its derivative instruments. The Company has the third-party preparer evaluate other readily available market prices for its derivative contracts as there is an active market for these contracts. The third-party preparer performs its independent valuation using a moment matching method similar to Turnbull-Wakeman for Asian options. The significant inputs used are crude oil prices, volatility, skew, discount rate and the contract terms of the derivative instruments. However, the Company does not have access to the specific proprietary valuation models or inputs used by its counterparties or third-party preparer. The Company compares the third-party preparer’s valuation to counterparty valuation statements, investigating any significant differences, and analyzes monthly valuation changes in relation to movements in crude oil forward price curves. The determination of the fair value for derivative instruments also incorporates a credit adjustment for non-performance risk, as required by GAAP. The Company calculated the credit adjustment for derivatives in a net asset position using current credit default swap values for each counterparty. The credit adjustment for derivatives in a net liability position is based on the Company’s market credit spread. Based on these calculations, the Company recorded a downward adjustment to the fair value of its net derivative liability of $0.4 million at September 30, 2013 and a downward adjustment to the fair value of its net derivative asset of $29,000 at December 31, 2012.
	Fair Value of Other Financial Instruments
	The Company’s financial instruments, including certain cash and cash equivalents, restricted cash, short-term investments, accounts receivable and accounts payable, are carried at cost, which approximates fair value due to the short-term maturity of these instruments. At September 30, 2013, the Company’s cash equivalents were all Level 1 assets. The carrying amount of the Company’s long-term debt reported in the Condensed Consolidated Balance Sheet at September 30, 2013 is $2,360.0 million, which includes $2,200.0 million of senior unsecured notes and $160.0 million of borrowings under the revolving credit facility (see Note 7 – Long-Term Debt). The fair value of the Company’s senior unsecured notes, which are Level 1 liabilities, is $2,325.0 million at September 30, 2013.
	Nonfinancial Assets and Liabilities
	Asset retirement obligations. The carrying amount of the Company’s ARO in the Condensed Consolidated Balance Sheet at September 30, 2013 is $27.4 million (see Note 8 – Asset Retirement Obligations). The Company determines the ARO by calculating the present value of estimated cash flows related to the liability. Estimating the future ARO requires management to make estimates and judgments regarding timing and existence of a liability, as well as what constitutes adequate restoration. Inherent in the fair value calculation are numerous assumptions and judgments, including the ultimate costs, inflation factors, credit adjusted discount rates, timing of settlement and changes in the legal, regulatory, environmental and political environments. These assumptions represent Level 3 inputs. To the extent future revisions to these assumptions impact the fair value of the existing ARO liability, a corresponding adjustment is made to the related asset.
	Impairment. The Company reviews its proved oil and natural gas properties for impairment whenever events and circumstances indicate that a decline in the recoverability of their carrying value may have occurred. The Company estimates the expected undiscounted future cash flows of its oil and natural gas properties and compares such undiscounted future cash flows to the carrying amount of the oil and natural gas properties to determine if the carrying amount is recoverable. If the carrying amount exceeds the estimated undiscounted future cash flows, the Company will adjust the carrying amount of the oil and natural gas properties to fair value. The factors used to determine fair value are subject to management’s judgment and expertise and include, but are not limited to, recent sales prices of comparable properties, the present value of future cash flows, net of estimated operating and development costs using estimates of proved reserves, future commodity pricing, future production estimates, anticipated capital expenditures and various discount rates commensurate with the risk and current market conditions associated with realizing the expected cash flows projected. These assumptions represent Level 3 inputs. No impairment charges on proved oil and natural gas properties were recorded for the three and nine months ended September 30, 2013 or 2012.

Derivative_Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative Instruments	'
	Derivative Instruments
	The Company utilizes derivative financial instruments to manage risks related to changes in oil prices. As of September 30, 2013, the Company utilized two-way and three-way costless collar options, put spreads, swaps and swaps with sub-floors to reduce the volatility of oil prices on a significant portion of its future expected oil production. A two-way collar is a combination of options: a sold call and a purchased put. The purchased put establishes a minimum price (floor) and the sold call establishes a maximum price (ceiling) the Company will receive for the volumes under contract. A three-way collar is a combination of options: a sold call, a purchased put and a sold put. The purchased put establishes a minimum price (floor), unless the market price falls below the sold put (sub-floor), at which point the minimum price would be NYMEX West Texas Intermediate (“WTI”) crude oil index price plus the difference between the purchased put and the sold put strike price. The sold call establishes a maximum price (ceiling) the Company will receive for the volumes under contract. A put spread is a combination of a purchased put and a sold put, and in this case does not include a sold call, allowing the volumes under this contract to have no established maximum price (ceiling). A swap is a sold call and a purchased put established at the same price (both ceiling and floor). A swap with a sub-floor is a swap coupled with a sold put (sub-floor) at which point the minimum price would be WTI crude oil index price plus the difference between the swap and the sold put strike price.
	All derivative instruments are recorded on the balance sheet as either assets or liabilities measured at fair value (see Note 5 – Fair Value Measurements). Derivative assets and liabilities arising from the Company’s derivative contracts with the same counterparty are also reported on a net basis, as all counterparty contracts provide for net settlement. The Company has not designated any derivative instruments as hedges for accounting purposes and does not enter into such instruments for speculative trading purposes. If a derivative does not qualify as a hedge or is not designated as a hedge, the changes in fair value, both cash settlements and non-cash changes in fair value, are recognized in the other income (expense) section of the Condensed Consolidated Statement of Operations as a net gain or loss on derivative instruments. The Company’s cash flow is only impacted when the actual settlements under the derivative contracts result in making a payment to or receiving a payment from the counterparty. These cash settlements are reflected as investing activities in the Company’s Condensed Consolidated Statement of Cash Flows.
	As of September 30, 2013, the Company had the following outstanding commodity derivative instruments, all of which settle monthly based on the average WTI crude oil index price:
	Settlement		Derivative		Total Notional			Weighted Average Prices											Fair Value
	Period		Instrument		Amount of Oil														Asset
								Swap				Sub-Floor			Floor		Ceiling		(Liability)
					(Barrels)			($/Barrel)											(In thousands)
	2013		Two-way collars		836,000										$	92.11	$	103.45	$	(2,636	)
	2013		Three-way collars		832,330							$	67.63		92.01		110.97		(118		)
	2013		Put spreads		168,670							70.89			90.89				4
	2013		Swaps		880,500			$	97.29										(5,118		)
	2014		Two-way collars		1,510,000										90.77		102.06		(159		)
	2014		Three-way collars		3,530,530							70.3			90.65		105.64		2,497
	2014		Put spreads		11,470							70			90				10
	2014		Swaps		2,218,500			95.87											(2,486		)
	2014		Swaps with sub-floors		2,004,000			92.6				70							(7,202		)
	2015		Two-way collars		108,500										90		99.86		284
	2015		Three-way collars		263,500							70.59			90.59		105.25		723
	2015		Swaps		108,500			93.07											148
	2015		Swaps with sub-floors		186,000			92.6				70							(80		)
																			$	(14,133	)
	The following table summarizes the location and fair value of all outstanding commodity derivative instruments recorded in the balance sheet for the periods presented:
	Fair Value of Derivative Instrument Assets (Liabilities)
				Fair Value
	Commodity	Balance Sheet Location		September 30,				31-Dec-12
				2013
				(In thousands)
	Crude oil	Derivative instruments — current assets		$	374			$	19,016
	Crude oil	Derivative instruments — non-current assets		3,405				4,981
	Crude oil	Derivative instruments — current liabilities		(17,060		)		(1,048		)
	Crude oil	Derivative instruments — non-current liabilities		(852		)		(380		)
	Total derivative instruments			$	(14,133	)		$	22,569
	The following table summarizes the location and amounts of gains and losses from the Company’s commodity derivative instruments for the periods presented:
				Three Months Ended								Nine Months Ended September 30,
				September 30,
		Income Statement Location		2013				2012				2013			2012
				(In thousands)
	Change in fair value of derivative instruments	Net gain (loss) on derivative instruments		$	(31,750	)		$	(27,690	)		$	(36,703	)	$	30,784
	Derivative settlements	Net gain (loss) on derivative instruments		(8,067		)		5,249				(5,135		)	2,784
	Total net gain (loss) on derivative instruments			$	(39,817	)		$	(22,441	)		$	(41,838	)	$	33,568
	The Company has adopted the FASB’s authoritative guidance on disclosures about offsetting assets and liabilities, which requires entities to disclose both gross and net information about instruments and transactions eligible for offset in the statement of financial position as well as instruments and transactions subject to an agreement similar to a master netting agreement. The Company’s derivative instruments are presented as assets and liabilities on a net basis by counterparty, as all counterparty contracts provide for net settlement. No margin or collateral balances are deposited with counterparties, and as such, gross amounts are offset to determine the net amounts presented in the Company’s Condensed Consolidated Balance Sheet.
	The following tables summarize gross and net information about the Company’s commodity derivative instruments for the periods presented:
	Offsetting of Derivative Assets		Gross Amounts of Recognized Assets				Gross Amounts Offset				Net Amounts of Assets Presented
							in the Balance Sheet				in the Balance Sheet
			(In thousands)
	As of September 30, 2013		$	32,895			$	(29,116	)		$	3,779
	As of December 31, 2012		68,970				(44,973		)		23,997
	Offsetting of Derivative Liabilities		Gross Amounts of Recognized Liabilities				Gross Amounts Offset				Net Amounts of Liabilities Presented
							in the Balance Sheet				in the Balance Sheet
			(In thousands)
	As of September 30, 2013		$	47,028			$	(29,116	)		$	17,912
	As of December 31, 2012		46,401				(44,973		)		1,428

LongTerm_Debt

Long-Term Debt	9 Months Ended
	Sep. 30, 2013
Debt Disclosure [Abstract]	'
Long-Term Debt	'
	Long-Term Debt
	Senior unsecured notes. On September 24, 2013, the Company issued $1,000.0 million of 6.875% senior unsecured notes due March 15, 2022 (the “2022 Notes”). The issuance of the 2022 Notes resulted in aggregate net proceeds to the Company of approximately $983.0 million. The Company used the proceeds from the 2022 Notes to fund the acquisition of oil and gas properties in its West Williston project area (see Note 15 – Subsequent Events). The proceeds of the 2022 Notes were held in escrow as of September 30, 2013, pending the closing of the acquisition. The acquisition subsequently closed on October 1, 2013, at which time the funds were released from escrow.
	In connection with the issuance of the 2022 Notes, the Company and Guarantors (as defined below) entered into a Registration Rights Agreement pursuant to which the Company and Guarantors agreed to file a registration statement with the SEC to allow the holders of the 2022 Notes to exchange the 2022 Notes for the same principal amount of a new issue of notes with substantially identical terms, except the new notes will be freely transferable under the Securities Act. The Company and the Guarantors will use commercially reasonable efforts to cause the exchange to be completed within 360 days after the 2022 Notes issuance date. Under certain circumstances, in lieu of a registered exchange offer, the Company must use commercially reasonable efforts to file a shelf registration statement for the resale of the 2022 Notes. If the Company fails to satisfy these obligations on a timely basis, the annual interest borne by the 2022 Notes will be increased by 1.0% per annum until the exchange offer is completed or the shelf registration statement is declared effective. The Company estimates the value of this contingent interest is immaterial at September 30, 2013.
	During 2011 and 2012, the Company issued $400.0 million of 7.25% senior unsecured notes due February 1, 2019 (the “2019 Notes”), $400.0 million of 6.5% senior unsecured notes due November 1, 2021 (the “2021 Notes”) and $400.0 million of 6.875% senior unsecured notes due January 15, 2023 (the “2023 Notes”, and together with the 2022 Notes, 2019 Notes and 2021 Notes, the “Notes”). The issuance of the 2019 Notes, 2021 Notes and the 2023 Notes resulted in aggregate net proceeds to the Company of approximately $1,175.8 million. The Company used the proceeds from the 2019 Notes, 2021 Notes and the 2023 Notes to fund its exploration, development and acquisition program and for general corporate purposes.
	Interest on the Notes is payable semi-annually in arrears. The Notes are guaranteed on a senior unsecured basis by the Company’s material subsidiaries (the “Guarantors”). These guarantees are full and unconditional and joint and several among the Guarantors, subject to certain customary release provisions, as follows:
	•	in connection with any sale or other disposition of all or substantially all of the assets of that Guarantor (including by way of merger or consolidation) to a person that is not (either before or after giving effect to such transaction) the Company or a restricted subsidiary of the Company;
	•	in connection with any sale or other disposition of the capital stock of that Guarantor (including by way of merger or consolidation) to a person that is not (either before or after giving effect to such transaction) the Company or a restricted subsidiary of the Company, such that, immediately after giving effect to such transaction, such Guarantor would no longer constitute a subsidiary of the Company;
	•	if the Company designates any restricted subsidiary that is a Guarantor to be an unrestricted subsidiary in accordance with the indenture;
	•	upon legal defeasance or satisfaction and discharge of the indenture; or
	•	upon the liquidation or dissolution of a Guarantor, provided no event of default occurs under the indentures as a result thereof.
	The Notes were issued under indentures containing provisions that are substantially the same, as amended and supplemented by supplemental indentures (collectively the “Indentures”), among the Company, the Guarantors and U.S. Bank National Association, as trustee (the “Trustee”). The Company has certain options to redeem up to 35% of the Notes at a certain redemption price based on a percentage of the principal amount, plus accrued and unpaid interest to the redemption date, with the proceeds of certain equity offerings so long as the redemption occurs within 180 days of completing such equity offering and at least 65% of the aggregate principal amount of the Notes remains outstanding after such redemption. Prior to certain dates, the Company has the option to redeem some or all of the Notes for cash at certain redemption prices equal to a certain percentage of their principal amount plus an applicable make-whole premium and accrued and unpaid interest to the redemption date. The Company estimates that the fair value of these redemption options is immaterial at September 30, 2013.
	The Indentures restrict the Company’s ability and the ability of certain of its subsidiaries to: (i) incur additional debt or enter into sale and leaseback transactions; (ii) pay distributions on, redeem or repurchase equity interests; (iii) make certain investments; (iv) incur liens; (v) enter into transactions with affiliates; (vi) merge or consolidate with another company; and (vii) transfer and sell assets. These covenants are subject to certain exceptions and qualifications. If at any time when the Notes are rated investment grade by both Moody’s Investors Service, Inc. and Standard & Poor’s Ratings Services and no Default (as defined in the Indentures) has occurred and is continuing, many of such covenants will terminate and the Company and its subsidiaries will cease to be subject to such covenants.
	The Indentures contain customary events of default, including:
	•	default in any payment of interest on any Note when due, continued for 30 days;
	•	default in the payment of principal or premium, if any, on any Note when due;
	•	failure by the Company to comply with its other obligations under the Indentures, in certain cases subject to notice and grace periods;
	•	payment defaults and accelerations with respect to other indebtedness of the Company and its Restricted Subsidiaries (as defined in the Indentures) in the aggregate principal amount of $10.0 million or more;
	•	certain events of bankruptcy, insolvency or reorganization of the Company or a Significant Subsidiary (as defined in the Indentures) or group of Restricted Subsidiaries that, taken together, would constitute a Significant Subsidiary;
	•	failure by the Company or any Significant Subsidiary or group of Restricted Subsidiaries that, taken together, would constitute a Significant Subsidiary to pay certain final judgments aggregating in excess of $10.0 million within 60 days; and
	•	any guarantee of the Notes by a Guarantor ceases to be in full force and effect, is declared null and void in a judicial proceeding or is denied or disaffirmed by its maker.
	Senior secured revolving line of credit. On April 5, 2013, the Company, as parent, and OPNA, as borrower, entered into a second amended and restated credit agreement (the “Second Amended Credit Facility”), which has a maturity date of April 5, 2018. In connection with entry into the Second Amended Credit Facility, the semi-annual redetermination of the Company’s borrowing base was also completed on April 5, 2013, which increased the borrowing base of the Second Amended Credit Facility from $750.0 million to $1,250.0 million. However, the Company elected to limit the aggregate commitment of the lenders under the Second Amended Credit Facility (the “Lenders”) to $900.0 million. The Company could have increased its aggregate commitment to the full $1,250.0 million borrowing base by increasing the commitment of one or more lenders. In addition, under the Second Amended Credit Facility, the overall credit facility increased from $1,000.0 million to $2,500.0 million. On September 3, 2013, the Company entered into an amendment to its Second Amended Credit Facility (the “Amendment”). In connection with the Amendment, the lenders under the Company’s revolving credit facility completed their regular semi-annual redetermination of the borrowing base scheduled for October 1, 2013. Following the redetermination, the Company’s borrowing base increased from $1,250.0 million to $1,500.0 million and elected commitments also totaled $1,500.0 million.
	The Second Amended Credit Facility is restricted to the borrowing base, which is reserve-based and subject to semi-annual redeterminations on April 1 and October 1 of each year. Borrowings under the Second Amended Credit Facility are collateralized by perfected first priority liens and security interests on substantially all of the Company’s assets, including mortgage liens on oil and natural gas properties having at least 80% of the reserve value as determined by reserve reports.
	Borrowings under the Second Amended Credit Facility are subject to varying rates of interest based on (1) the total outstanding borrowings (including the value of all outstanding letters of credit) in relation to the borrowing base and (2) whether the loan is a London interbank offered rate (“LIBOR”) loan or a domestic bank prime interest rate loan (defined in the Second Amended Credit Facility as an Alternate Based Rate or “ABR” loan). As of September 30, 2013, any outstanding LIBOR and ABR loans bore their respective interest rates plus the applicable margin indicated in the following table:
	Ratio of Total Outstanding Borrowings to Borrowing Base		Applicable Margin		Applicable Margin
			for LIBOR Loans		for ABR Loans
	Less than .25 to 1		1.5	%	0	%
	Greater than or equal to .25 to 1 but less than .50 to 1		1.75	%	0.25	%
	Greater than or equal to .50 to 1 but less than .75 to 1		2	%	0.5	%
	Greater than or equal to .75 to 1 but less than .90 to 1		2.25	%	0.75	%
	Greater than .90 to 1 but less than or equal 1		2.5	%	1	%
	An ABR loan may be repaid at any time before the scheduled maturity of the Second Amended Credit Facility upon the Company providing advance notification to the Lenders. Interest is paid quarterly on ABR loans based on the number of days an ABR loan is outstanding as of the last business day in March, June, September and December. The Company has the option to convert an ABR loan to a LIBOR-based loan upon providing advance notification to the Lenders. The minimum available loan term is one month and the maximum loan term is six months for LIBOR-based loans. Interest for LIBOR loans is paid upon maturity of the loan term. Interim interest is paid every three months for LIBOR loans that have loan terms greater than three months in duration. At the end of a LIBOR loan term, the Second Amended Credit Facility allows the Company to elect to repay the borrowing, continue a LIBOR loan with the same or a differing loan term or convert the borrowing to an ABR loan.
	On a quarterly basis, the Company pays a 0.375% (as of September 30, 2013) annualized commitment fee on the average amount of borrowing base capacity not utilized during the quarter and fees calculated on the average amount of letter of credit balances outstanding during the quarter.
	As of September 30, 2013, the Second Amended Credit Facility contained covenants that included, among others:
	•	a prohibition against incurring debt, subject to permitted exceptions;
	•	a prohibition against making dividends, distributions and redemptions, subject to permitted exceptions;
	•	a prohibition against making investments, loans and advances, subject to permitted exceptions;
	•	restrictions on creating liens and leases on the assets of the Company and its subsidiaries, subject to permitted exceptions;
	•	restrictions on merging and selling assets outside the ordinary course of business;
	•	restrictions on use of proceeds, investments, transactions with affiliates or change of principal business;
	•	a provision limiting oil and natural gas derivative financial instruments;
	•	a requirement that the Company maintain a ratio of consolidated EBITDAX (as defined in the Second Amended Credit Facility) to consolidated Interest Expense (as defined in the Second Amended Credit Facility) of no less than 2.5 to 1.0 for the four quarters ended on the last day of each quarter; and
	•	a requirement that the Company maintain a Current Ratio (as defined in the Second Amended Credit Facility) of consolidated current assets (with exclusions as described in the Second Amended Credit Facility) to consolidated current liabilities (with exclusions as described in the Second Amended Credit Facility) of not less than 1.0 to 1.0 as of the last day of any fiscal quarter.
	The Second Amended Credit Facility contains customary events of default. If an event of default occurs and is continuing, the Lenders may declare all amounts outstanding under the Second Amended Credit Facility to be immediately due and payable.
	As of September 30, 2013, the Company had $160.0 million of LIBOR loans and $5.2 million of outstanding letters of credit issued under the Second Amended Credit Facility, resulting in an unused borrowing base capacity of $1,334.8 million. The weighted average interest rate incurred on the outstanding Second Amended Credit Facility borrowings for both the three and nine months ended September 30, 2013 was 2.8%. The Company was in compliance with the financial covenants of the Second Amended Credit Facility as of September 30, 2013.
	Deferred financing costs. As of September 30, 2013, the Company had $42.3 million of deferred financing costs related to the Notes and the Second Amended Credit Facility. The deferred financing costs are included in deferred costs and other assets on the Company’s Condensed Consolidated Balance Sheet at September 30, 2013 and are being amortized over the respective terms of the Notes and the Second Amended Credit Facility. Amortization of deferred financing costs recorded for the three and nine months ended September 30, 2013 was $1.0 million and $2.9 million, respectively, and $0.8 million and $2.1 million for the three and nine months ended September 30, 2012, respectively. These costs are included in interest expense on the Company’s Condensed Consolidated Statement of Operations.

Asset_Retirement_Obligations

Asset Retirement Obligations	9 Months Ended
	Sep. 30, 2013
Asset Retirement Obligation Disclosure [Abstract]	'
Asset Retirement Obligations	'
	Asset Retirement Obligations
	The following table reflects the changes in the Company’s ARO during the nine months ended September 30, 2013:
		(In thousands)
	Balance at December 31, 2012	$	23,234
	Liabilities incurred during period	3,066
	Liabilities settled during period	23
	Accretion expense during period (1)	895
	Revisions to estimates	213
	Balance at September 30, 2013	$	27,431
	___________________
	-1	Included in depreciation, depletion and amortization on the Company’s Condensed Consolidated Statement of Operations.
	At September 30, 2013, the current portion of the total ARO balance was approximately $0.4 million and is included in accrued liabilities on the Company’s Condensed Consolidated Balance Sheet.

StockBased_Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Stock-Based Compensation	'
	Stock-Based Compensation
	Restricted stock awards. The Company has granted restricted stock awards to employees and directors under its 2010 Long-Term Incentive Plan, the majority of which vest over a three-year period. The fair value of restricted stock grants is based on the value of the Company’s common stock on the date of grant. Compensation expense is recognized ratably over the requisite service period. Beginning January 1, 2013, the Company assumed annual forfeiture rates by employee group ranging from 0% to 11% based on the Company’s forfeiture history for this type of award as adjusted for management’s expectations of forfeitures.
	Stock-based compensation expense recorded for restricted stock awards for the three and nine months ended September 30, 2013 was $2.6 million and $7.1 million, respectively. For the three and nine months ended September 30, 2012, stock-based compensation expense recorded for restricted stock awards was $2.6 million and $6.5 million, respectively. Stock-based compensation expense is included in general and administrative expenses on the Company’s Condensed Consolidated Statement of Operations.
	Performance share units. The Company has granted performance share units (“PSUs”) to officers of the Company under its 2010 Long-Term Incentive Plan. The PSUs are awards of restricted stock units, and each PSU that is earned represents the right to receive one share of the Company’s common stock.
	Each grant of PSUs is subject to a designated three-year initial performance period. The number of PSUs to be earned is subject to a market condition, which is based on a comparison of the total shareholder return (“TSR”) achieved with respect to shares of the Company’s common stock against the TSR achieved by a defined peer group at the end of the performance period. Depending on the Company’s performance relative to the defined peer group, an award recipient will earn between 0% and 200% of the initial PSUs granted. If less than 200% of the initial PSUs granted are earned at the end of the initial performance period, then the performance period will be extended an additional year to give the recipient the opportunity to earn up to an aggregate of 200% of the initial PSUs granted.
	The following table summarizes PSUs held by the Company’s officers at September 30, 2013:
		PSUs		Weighted Average
				Grant Date Fair Value
				per Unit
	Non-vested PSUs at December 31, 2012	155,220		$	26.22
	Granted	135,620		42.01
	Vested	—		—
	Forfeited	(21,540	)	32.89
	Non-vested PSUs at September 30, 2013	269,300		$	33.64
	The Company accounted for these PSUs as equity awards pursuant to the FASB’s authoritative guidance for share-based payments. The aggregate grant date fair value of the market-based awards was determined using a Monte Carlo simulation model, which results in an expected percentage of PSUs earned. The fair value of these PSUs is recognized on a straight-line basis over the performance period. As it is probable that a portion of the awards will be earned during the extended performance period, the grant date fair value will be amortized over four years. However, if 200% of the initial PSUs granted are earned at the end of the initial performance period, then the remaining compensation expense will be accelerated in order to be fully recognized over three years. All compensation expense related to the PSUs will be recognized if the requisite performance period is fulfilled, even if the market condition is not achieved.
	The Monte Carlo simulation model uses assumptions regarding random projections and must be repeated numerous times to achieve a probabilistic assessment. The key valuation assumptions for the Monte Carlo model are the forecast period, initial value, risk-free rate, volatility and correlation coefficients. The risk-free rate is the U.S. treasury rate on the date of grant. The initial value is the average of the volume weighted average prices for the 30 trading days prior to the start of the performance cycle for the Company and each of its peers. Volatility is the standard deviation of the average percentage in stock price over a historical two-year period for the Company and each of its peers. The correlation coefficients are measures of the strength of the linear relationship between and amongst the Company and its peers estimated based on historical stock price data. Beginning January 1, 2013, the Company assumed an annual forfeiture rate of 2.7% based on management’s expectations of forfeitures for all PSUs granted.
	The following assumptions were used for the Monte Carlo model to determine the grant date fair value and associated stock-based compensation expense of the PSUs granted:
		2013 Grants		2012 Grants
	Forecast period (years)	4		4.01
	Risk-free rate	0.65	%	0.46	%
	Oasis volatility	47.48	%	51	%
	Based on these assumptions, the Monte Carlo simulation model resulted in an expected percentage of PSUs earned of 112% and 98% for the 2013 and 2012 grants, respectively. Stock-based compensation expense recorded for PSUs for the three and nine months ended September 30, 2013 was $0.5 million and $1.3 million, respectively, and is included in general and administrative expenses on the Condensed Consolidated Statement of Operations. Stock-based compensation expense recorded for PSUs for both the three and nine months ended September 30, 2012 was $0.2 million.

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2013
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Income Taxes
	The Company’s effective tax rate for the three and nine months ended September 30, 2013 was 38.2% and 37.2%, respectively. The Company’s effective tax rate for the three and nine months ended September 30, 2012 was 38.5% and 37.6%, respectively. These rates were consistent with the statutory tax rate applicable to the U.S. and the blended state rate for the states in which the Company conducts business. As of September 30, 2013, the Company did not have any uncertain tax positions requiring adjustments to its tax liability.
	The Company had deferred tax assets for its federal and state tax loss carryforwards at September 30, 2013 recorded in current deferred taxes. Deferred tax assets are reduced by a valuation allowance when, in the opinion of management, it is more likely than not that some portion or all of the deferred tax assets will not be realized. As of September 30, 2013, management determined that a valuation allowance was not required for the tax loss carryforwards as they are expected to be fully utilized before expiration.

Earnings_Per_Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Earnings Per Share	'
	Earnings Per Share
	Basic earnings per share is computed by dividing income available to common stockholders by the weighted average number of shares outstanding for the periods presented. The calculation of diluted earnings per share includes the impact of potentially dilutive non-vested restricted shares outstanding during the periods presented, unless their effect is anti-dilutive. There are no adjustments made to income available to common stockholders in the calculation of diluted earnings per share.
	The following is a calculation of the basic and diluted weighted-average shares outstanding for the three and nine months ended September 30, 2013 and 2012:
		Three Months Ended		Nine Months Ended September 30,
		September 30,
		2013	2012	2013	2012
		(In thousands)
	Basic weighted average common shares outstanding	92,449	92,186	92,408	92,164
	Dilution effect of stock awards at end of period	387	230	430	179
	Diluted weighted average common shares outstanding	92,836	92,416	92,838	92,343
	Anti-dilutive stock-based compensation awards	789	748	719	541

Business_Segment_Information

Business Segment Information	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]	'
Business Segment Information	'
	Business Segment Information
	In the first quarter of 2012, the Company began its well services business segment (OWS) to perform completion services for the Company’s oil and natural gas wells operated by OPNA. Revenues for the well services segment are derived from providing well completion services and related product sales. In the first quarter of 2013, the Company formed its midstream services business segment (OMS) to perform salt water disposal and other midstream services for the Company’s oil and natural gas wells operated by OPNA. Revenues for the midstream segment are primarily derived from providing salt water disposal services. Prior to 2013, the salt water disposal systems were owned by OPNA, and the related income was included as a reduction to lease operating expenses. The revenues and expenses related to work performed by OWS and OMS for OPNA’s working interests are eliminated in consolidation, and only the revenues and expenses related to non-affiliated working interest owners are included in the Company’s Condensed Consolidated Statement of Operations. Prior to 2012, the Company only operated its exploration and production segment. The exploration and production segment is engaged in the acquisition and development of oil and natural gas properties and includes the complementary marketing services provided by OPM. Revenues for the exploration and production segment are primarily derived from the sale of oil and natural gas production. These segments represent the Company’s three current operating units, each offering different products and services. The Company’s corporate activities have been allocated to the supported business segments accordingly.
	Management evaluates the performance of the Company’s business segments based on operating income, which is defined as segment operating revenues less expenses. Summarized financial information for the Company’s segments is shown in the following table:
		Exploration and			Well Services			Midstream Services			Consolidated
		Production
		(In thousands)
	Three Months Ended September 30, 2013:
	Revenues	$	286,952		$	57,116		$	7,597		$	351,665
	Inter-segment revenues	—			(40,026		)	(6,141		)	(46,167		)
	Total revenues	286,952			17,090			1,456			305,498
	Operating income	140,765			5,870			4,227			150,862
	Other income (expense)	(62,628		)	(20		)	—			(62,648		)
	Income before income taxes	78,137			5,850			4,227			88,214
	Three Months Ended September 30, 2012:
	Revenues	$	178,748		$	37,160		$	—		$	215,908
	Inter-segment revenues	—			(31,197		)	—			(31,197		)
	Total revenues	178,748			5,963			—			184,711
	Operating income (loss)	89,279			(17,241		)	—			72,038
	Other income (expense)	(42,273		)	—			—			(42,273		)
	Income (loss) before income taxes	47,006			(17,241		)	—			29,765
	Nine Months Ended September 30, 2013:
	Revenues	$	770,445		$	124,266		$	19,451		$	914,162
	Inter-segment revenues	—			(90,000		)	(15,778		)	(105,778		)
	Total revenues	770,445			34,266			3,673			808,384
	Operating income	359,121			11,744			11,400			382,265
	Other income (expense)	(106,159		)	(11		)	—			(106,170		)
	Income before income taxes	252,962			11,733			11,400			276,095
	Nine Months Ended September 30, 2012:
	Revenues	$	461,857		$	54,909		$	—		$	516,766
	Inter-segment revenues	—			(44,425		)	—			(44,425		)
	Total revenues	461,857			10,484			—			472,341
	Operating income	190,257			116			—			190,373
	Other income (expense)	(12,863		)	—			—			(12,863		)
	Income before income taxes	177,394			116			—			177,510
	Total Assets:
	As of September 30, 2013	$	3,916,554		$	68,869		$	97,960		$	4,083,383
	As of December 31, 2012	2,475,820			52,974			—			2,528,794

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	Commitments and Contingencies
	Lease obligations. The Company’s total rental commitments under leases for office space and other property and equipment at September 30, 2013 were $11.5 million.
	Drilling contracts. As of September 30, 2013, the Company had certain drilling rig contracts with initial terms greater than one year. In the event of early contract termination under these contracts, the Company would be obligated to pay approximately $24.9 million as of September 30, 2013 for the days remaining through the end of the primary terms of the contracts.
	Volume commitment agreements. As of September 30, 2013, the Company had certain agreements with an aggregate requirement to deliver a minimum quantity of approximately 14.3 MMBbl and 12.8 Bcf from its Williston Basin project areas within specified timeframes, all of which are less than six years. Future obligations under these agreements were approximately $55.5 million as of September 30, 2013.
	Investment commitment. As of September 30, 2013, the Company had a remaining capital commitment to invest, expend and/or incur expenses of $7.2 million in connection with drilling and completion activities for certain wells located in the Company’s East Nesson project area, in exchange for the transfer of assets in connection with the East Nesson Acquisitions.
	Litigation. The Company is party to various legal and/or regulatory proceedings from time to time arising in the ordinary course of business. The Company believes all such matters are without merit and involve amounts which, if resolved unfavorably, either individually or in the aggregate, will not have a material adverse effect on its financial condition, results of operations or cash flows.

Condensed_Consolidating_Financ

Condensed Consolidating Financial Information	9 Months Ended
	Sep. 30, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Condensed Consolidating Financial Information	'
	Condensed Consolidating Financial Information
	The Notes (see Note 7) are guaranteed on a senior unsecured basis by the Guarantors, which are 100% owned by the Company. These guarantees are full and unconditional and joint and several among the Guarantors. Certain of the Company’s immaterial wholly owned subsidiaries do not guarantee the Notes (“Non-Guarantor Subsidiaries”).
	The following financial information reflects consolidating financial information of the Company (“Issuer”) and its Guarantors on a combined basis, prepared on the equity basis of accounting. The Non-Guarantor Subsidiaries are immaterial and, therefore, not presented separately. The information is presented in accordance with the requirements of Rule 3-10 under the SEC’s Regulation S-X. The financial information may not necessarily be indicative of results of operations, cash flows or financial position had the Guarantors operated as independent entities. The Company has not presented separate financial and narrative information for each of the Guarantors because it believes such financial and narrative information would not provide any additional information that would be material in evaluating the sufficiency of the Guarantors.
	Condensed Consolidating Balance Sheet
	(In thousands, except share data)
		30-Sep-13
		Parent/			Combined			Intercompany			Consolidated
		Issuer			Guarantor			Eliminations
					Subsidiaries
	ASSETS
	Current assets
	Cash and cash equivalents	$	32,955		$	92,485		$	—		$	125,440
	Restricted cash	986,210			—			—			986,210
	Accounts receivable – oil and gas revenues	—			155,068			—			155,068
	Accounts receivable – joint interest partners	—			120,058			—			120,058
	Accounts receivable – from affiliates	770			8,432			(9,202		)	—
	Inventory	—			18,358			—			18,358
	Prepaid expenses	477			6,963			—			7,440
	Advances to joint interest partners	—			1,170			—			1,170
	Derivative instruments	—			374			—			374
	Deferred income taxes	—			8,683			—			8,683
	Other current assets	2			471			—			473
	Total current assets	1,020,414			412,062			(9,202		)	1,423,274
	Property, plant and equipment
	Oil and gas properties (successful efforts method)	—			3,044,515			—			3,044,515
	Other property and equipment	—			157,926			—			157,926
	Less: accumulated depreciation, depletion, amortization and impairment	—			(589,173		)	—			(589,173		)
	Total property, plant and equipment, net	—			2,613,268			—			2,613,268
	Investments in and advances to subsidiaries	2,082,828			—			(2,082,828		)	—
	Derivative instruments	—			3,405			—			3,405
	Deferred income taxes	69,795			—			(69,795		)	—
	Deferred costs and other assets	34,128			9,308			—			43,436
	Total assets	$	3,207,165		$	3,038,043		$	(2,161,825	)	$	4,083,383
	LIABILITIES AND STOCKHOLDERS’ EQUITY
	Current liabilities
	Accounts payable	$	—		$	39,468		$	—		$	39,468
	Accounts payable – from affiliates	8,432			770			(9,202		)	—
	Advances from joint interest partners	—			13,211			—			13,211
	Revenues and production taxes payable	—			133,083			—			133,083
	Accrued liabilities	46			198,447			—			198,493
	Accrued interest payable	22,809			64			—			22,873
	Derivative instruments	—			17,060			—			17,060
	Total current liabilities	31,287			402,103			(9,202		)	424,188
	Long-term debt	2,200,000			160,000			—			2,360,000
	Asset retirement obligations	—			26,999			—			26,999
	Derivative instruments	—			852			—			852
	Deferred income taxes	—			362,951			(69,795		)	293,156
	Other liabilities	—			2,310			—			2,310
	Total liabilities	2,231,287			955,215			(78,997		)	3,107,505
	Stockholders’ equity
	Capital contributions from affiliates	—			1,643,729			(1,643,729		)	—
	Common stock, $0.01 par value; 300,000,000 shares authorized; 93,854,867 issued and 93,690,494 outstanding	926			—			—			926
	Treasury stock, at cost; 164,373 shares	(5,220		)	—			—			(5,220		)
	Additional paid-in-capital	666,770			8,743			(8,743		)	666,770
	Retained earnings	313,402			430,356			(430,356		)	313,402
	Total stockholders’ equity	975,878			2,082,828			(2,082,828		)	975,878
	Total liabilities and stockholders’ equity	$	3,207,165		$	3,038,043		$	(2,161,825	)	$	4,083,383
	Condensed Consolidating Balance Sheet
	(In thousands, except share data)
		31-Dec-12
		Parent/			Combined			Intercompany			Consolidated
		Issuer			Guarantor			Eliminations
					Subsidiaries
ASSETS
Current assets
Cash and cash equivalents	$	133,797		$	79,650		$	—		$	213,447
Short-term investments	25,891			—			—			25,891
Accounts receivable – oil and gas revenues	—			110,341			—			110,341
Accounts receivable – joint interest partners	—			99,194			—			99,194
Accounts receivable – from affiliates	310			5,845			(6,155		)	—
Inventory	—			20,707			—			20,707
Prepaid expenses	313			1,457			—			1,770
Advances to joint interest partners	—			1,985			—			1,985
Derivative instruments	—			19,016			—			19,016
Other current assets	235			100			—			335
Total current assets	160,546			338,295			(6,155		)	492,686
Property, plant and equipment
Oil and gas properties (successful efforts method)	—			2,348,128			—			2,348,128
Other property and equipment	—			49,732			—			49,732
Less: accumulated depreciation, depletion, amortization and impairment	—			(391,260		)	—			(391,260		)
Total property, plant and equipment, net	—			2,006,600			—			2,006,600
Investments in and advances to subsidiaries	1,807,010			—			(1,807,010		)	—
Derivative instruments	—			4,981			—			4,981
Deferred income taxes	42,746			—			(42,746		)	—
Deferred costs and other assets	20,748			3,779			—			24,527
Total assets	$	2,031,050		$	2,353,655		$	(1,855,911	)	$	2,528,794
LIABILITIES AND STOCKHOLDERS’ EQUITY
Current liabilities
Accounts payable	$	9		$	12,482		$	—		$	12,491
Accounts payable – from affiliates	5,845			310			(6,155		)	—
Advances from joint interest partners	—			21,176			—			21,176
Revenues and production taxes payable	—			71,553			—			71,553
Accrued liabilities	100			189,763			—			189,863
Accrued interest payable	30,091			5			—			30,096
Derivative instruments	—			1,048			—			1,048
Deferred income taxes	—			4,558			—			4,558
Total current liabilities	36,045			300,895			(6,155		)	330,785
Long-term debt	1,200,000			—			—			1,200,000
Asset retirement obligations	—			22,956			—			22,956
Derivative instruments	—			380			—			380
Deferred income taxes	—			220,417			(42,746		)	177,671
Other liabilities	—			1,997			—			1,997
Total liabilities	1,236,045			546,645			(48,901		)	1,733,789
Stockholders’ equity
Capital contributions from affiliates	—			1,586,780			(1,586,780		)	—
Common stock, $0.01 par value; 300,000,000 shares authorized; 93,432,712 issued and 93,303,298 outstanding	925			—			—			925
Treasury stock, at cost; 129,414 shares	(3,796		)	—			—			(3,796		)
Additional paid-in-capital	657,943			8,743			(8,743		)	657,943
Retained earnings	139,933			211,487			(211,487		)	139,933
Total stockholders’ equity	795,005			1,807,010			(1,807,010		)	795,005
Total liabilities and stockholders’ equity	$	2,031,050		$	2,353,655		$	(1,855,911	)	$	2,528,794
Condensed Consolidating Statement of Operations
(In thousands)
	Three Months Ended September 30, 2013
	Parent/			Combined			Intercompany			Consolidated
	Issuer			Guarantor			Eliminations
				Subsidiaries
Revenues
Oil and gas revenues	$	—		$	286,952		$	—		$	286,952
Well services and midstream revenues	—			18,546			—			18,546
Total revenues	—			305,498			—			305,498
Expenses
Lease operating expenses	—			21,831			—			21,831
Well services and midstream operating expenses	—			10,319			—			10,319
Marketing, transportation and gathering expenses	—			5,688			—			5,688
Production taxes	—			26,823			—			26,823
Depreciation, depletion and amortization	—			72,728			—			72,728
Exploration expenses	—			463			—			463
Impairment of oil and gas properties	—			56			—			56
General and administrative expenses	3,746			12,982			—			16,728
Total expenses	3,746			150,890			—			154,636
Operating income (loss)	(3,746		)	154,608			—			150,862
Other income (expense)
Equity in earnings in subsidiaries	70,118			—			(70,118		)	—
Net loss on derivative instruments	—			(39,817		)	—			(39,817		)
Interest expense, net of capitalized interest	(21,277		)	(1,577		)	—			(22,854		)
Other income	15			8			—			23
Total other income (expense)	48,856			(41,386		)	(70,118		)	(62,648		)
Income before income taxes	45,110			113,222			(70,118		)	88,214
Income tax benefit (expense)	9,389			(43,104		)	—			(33,715		)
Net income	$	54,499		$	70,118		$	(70,118	)	$	54,499
Condensed Consolidating Statement of Operations
(In thousands)
	Three Months Ended September 30, 2012
	Parent/			Combined			Intercompany			Consolidated
	Issuer			Guarantor			Eliminations
				Subsidiaries
Revenues
Oil and gas revenues	$	—		$	178,748		$	—		$	178,748
Well services revenues	—			5,963			—			5,963
Total revenues	—			184,711			—			184,711
Expenses
Lease operating expenses	—			16,134			—			16,134
Well services operating expenses	—			5,420			—			5,420
Marketing, transportation and gathering expenses	—			2,744			—			2,744
Production taxes	—			16,433			—			16,433
Depreciation, depletion and amortization	—			57,684			—			57,684
Exploration expenses	—			336			—			336
Impairment of oil and gas properties	—			36			—			36
General and administrative expenses	2,988			10,898			—			13,886
Total expenses	2,988			109,685			—			112,673
Operating income (loss)	(2,988		)	75,026			—			72,038
Other income (expense)
Equity in earnings in subsidiaries	32,735			—			(32,735		)	—
Net loss on derivative instruments	—			(22,441		)	—			(22,441		)
Interest expense, net of capitalized interest	(20,307		)	(672		)	—			(20,979		)
Other income	238			909			—			1,147
Total other income (expense)	12,666			(22,204		)	(32,735		)	(42,273		)
Income before income taxes	9,678			52,822			(32,735		)	29,765
Income tax benefit (expense)	8,636			(20,087		)	—			(11,451		)
Net income	$	18,314		$	32,735		$	(32,735	)	$	18,314
Condensed Consolidating Statement of Operations
(In thousands)
	Nine Months Ended September 30, 2013
	Parent/			Combined			Intercompany			Consolidated
	Issuer			Guarantor			Eliminations
				Subsidiaries
Revenues
Oil and gas revenues	$	—		$	770,445		$	—		$	770,445
Well services and midstream revenues	—			37,939			—			37,939
Total revenues	—			808,384			—			808,384
Expenses
Lease operating expenses	—			59,586			—			59,586
Well services and midstream operating expenses	—			19,877			—			19,877
Marketing, transportation and gathering expenses	—			19,856			—			19,856
Production taxes	—			70,309			—			70,309
Depreciation, depletion and amortization	—			205,779			—			205,779
Exploration expenses	—			2,712			—			2,712
Impairment of oil and gas properties	—			762			—			762
General and administrative expenses	10,146			37,092			—			47,238
Total expenses	10,146			415,973			—			426,119
Operating income (loss)	(10,146		)	392,411			—			382,265
Other income (expense)
Equity in earnings in subsidiaries	218,869			—			(218,869		)	—
Net loss on derivative instruments	—			(41,838		)	—			(41,838		)
Interest expense, net of capitalized interest	(61,955		)	(3,474		)	—			(65,429		)
Other income	(348		)	1,445			—			1,097
Total other income (expense)	156,566			(43,867		)	(218,869		)	(106,170		)
Income before income taxes	146,420			348,544			(218,869		)	276,095
Income tax benefit (expense)	27,049			(129,675		)	—			(102,626		)
Net income	$	173,469		$	218,869		$	(218,869	)	$	173,469
Condensed Consolidating Statement of Operations
(In thousands)
	Nine Months Ended September 30, 2012
	Parent/			Combined			Intercompany			Consolidated
	Issuer			Guarantor			Eliminations
				Subsidiaries
Revenues
Oil and gas revenues	$	—		$	461,857		$	—		$	461,857
Well services and midstream revenues	—			10,484			—			10,484
Total revenues	—			472,341			—			472,341
Expenses
Lease operating expenses	—			37,979			—			37,979
Well services and midstream operating expenses	—			7,104			—			7,104
Marketing, transportation and gathering expenses	—			7,283			—			7,283
Production taxes	—			43,419			—			43,419
Depreciation, depletion and amortization	—			140,783			—			140,783
Exploration expenses	—			3,171			—			3,171
Impairment of oil and gas properties	—			2,607			—			2,607
General and administrative expenses	8,078			31,544			—			39,622
Total expenses	8,078			273,890			—			281,968
Operating income (loss)	(8,078		)	198,451			—			190,373
Other income (expense)
Equity in earnings in subsidiaries	145,021			—			(145,021		)	—
Net gain on derivative instruments	—			33,568			—			33,568
Interest expense, net of capitalized interest	(47,136		)	(1,816		)	—			(48,952		)
Other income	533			1,988			—			2,521
Total other income (expense)	98,418			33,740			(145,021		)	(12,863		)
Income before income taxes	90,340			232,191			(145,021		)	177,510
Income tax benefit (expense)	20,458			(87,170		)	—			(66,712		)
Net income	$	110,798		$	145,021		$	(145,021	)	$	110,798
Condensed Consolidating Statement of Cash Flows
(In thousands)
	Nine Months Ended September 30, 2013
	Parent/			Combined			Intercompany			Consolidated
	Issuer			Guarantor			Eliminations
				Subsidiaries
Cash flows from operating activities:
Net income	$	173,469		$	218,869		$	(218,869	)	$	173,469
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Equity in earnings of subsidiaries	(218,869		)	—			218,869			—
Depreciation, depletion and amortization	—			205,779			—			205,779
Impairment of oil and gas properties	—			762			—			762
Deferred income taxes	(27,049		)	129,293			—			102,244
Derivative instruments	—			41,838			—			41,838
Stock-based compensation expenses	8,196			215			—			8,411
Debt discount amortization and other	2,850			(157		)	—			2,693
Working capital and other changes:
Change in accounts receivable	(460		)	(69,614		)	2,587			(67,487		)
Change in inventory	—			(8,820		)	—			(8,820		)
Change in prepaid expenses	(164		)	(5,011		)	—			(5,175		)
Change in other current assets	233			(371		)	—			(138		)
Change in other assets	—			(63		)	—			(63		)
Change in accounts payable and accrued liabilities	(4,758		)	89,591			(2,587		)	82,246
Change in other current liabilities	—			—			—			—
Change in other liabilities	—			922			—			922
Net cash provided by (used in) operating activities	(66,552		)	603,233			—			536,681
Cash flows from investing activities:
Capital expenditures	—			(654,175		)	—			(654,175		)
Acquisitions of oil and gas properties	—			(133,061		)	—			(133,061		)
Increase in restricted cash	(986,210		)	—			—			(986,210		)
Derivative settlements	—			(5,135		)	—			(5,135		)
Redemptions of short-term investments	25,000			—			—			25,000
Advances from joint interest partners	—			(7,965		)	—			(7,965		)
Net cash used in investing activities	(961,210		)	(800,336		)	—			(1,761,546		)
Cash flows from financing activities:
Proceeds from credit facility	—			160,000			—			160,000
Proceeds from issuance of senior notes	1,000,000			—			—			1,000,000
Purchases of treasury stock	(1,424		)	—			—			(1,424		)
Debt issuance costs	(15,340		)	(6,378		)	—			(21,718		)
Investment in / capital contributions from affiliates	(56,316		)	56,316			—			—
Net cash provided by financing activities	926,920			209,938			—			1,136,858
Increase (decrease) in cash and cash equivalents	(100,842		)	12,835			—			(88,007		)
Cash and cash equivalents at beginning of period	133,797			79,650			—			213,447
Cash and cash equivalents at end of period	$	32,955		$	92,485		$	—		$	125,440
Condensed Consolidating Statement of Cash Flows
(In thousands)
	Nine Months Ended September 30, 2012
	Parent/			Combined			Intercompany			Consolidated
	Issuer			Guarantor			Eliminations
				Subsidiaries
Cash flows from operating activities:
Net income	$	110,798		$	145,021		$	(145,021	)	$	110,798
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries	(145,021		)	—			145,021			—
Depreciation, depletion and amortization	—			140,783			—			140,783
Impairment of oil and gas properties	—			2,607			—			2,607
Deferred income taxes	(20,458		)	87,106			—			66,648
Derivative instruments	—			(33,568		)	—			(33,568		)
Stock-based compensation expenses	6,397			230			—			6,627
Debt discount amortization and other	1,616			422			—			2,038
Working capital and other changes:
Change in accounts receivable	(203		)	(70,899		)	1,939			(69,163		)
Change in inventory	—			(26,790		)	—			(26,790		)
Change in prepaid expenses	(192		)	(1,817		)	—			(2,009		)
Change in other current assets	(60		)	473			—			413
Change in other assets	(24		)	(95		)	—			(119		)
Change in accounts payable and accrued liabilities	8,620			72,398			(1,939		)	79,079
Change in other current liabilities	—			4,784			—			4,784
Net cash provided by operating activities	(38,527		)	320,655			—			282,128
Cash flows from investing activities:
Capital expenditures	—			(777,516		)	—			(777,516		)
Derivative settlements	—			2,784			—			2,784
Purchases of short-term investments	(126,213		)	—			—			(126,213		)
Redemptions of short-term investments	19,994			—			—			19,994
Advances from joint interest partners	—			17,508			—			17,508
Net cash used in investing activities	(106,219		)	(757,224		)	—			(863,443		)
Cash flows from financing activities:
Proceeds from issuance of senior notes	400,000			—						400,000
Purchases of treasury stock	(1,299		)	—			—			(1,299		)
Debt issuance costs	(7,255		)	(700		)	—			(7,955		)
Investment in / capital contributions from affiliates	(459,012		)	459,012			—			—
Net cash provided by (used in) financing activities	(67,566		)	458,312			—			390,746
Increase (decrease) in cash and cash equivalents	(212,312		)	21,743			—			(190,569		)
Cash and cash equivalents at beginning of period	443,482			27,390			—			470,872
Cash and cash equivalents at end of period	$	231,170		$	49,133		$	—		$	280,303

Subsequent_Events

Subsequent Events	9 Months Ended
	Sep. 30, 2013
Subsequent Events [Abstract]	'
Subsequent Events	'
	Subsequent Events
	The Company has evaluated the period after the balance sheet date, noting no subsequent events or transactions that required recognition or disclosure in the financial statements, other than as noted below.
	West Williston acquisition. On October 1, 2013, the Company acquired approximately 136,000 net acres in and around its position in North Dakota in its West Williston project area (the “West Williston Acquisition”) for $1,478.6 million, which included a $72.5 million deposit made in September 2013, and is subject to further customary post close adjustments. The Company funded the West Williston Acquisition with proceeds from its issuance of the 2022 Notes and borrowings under its revolving credit facility (see below and Note 7 – Long-Term Debt). The West Williston Acquisition will be accounted for as a business combination.
	Senior secured revolving line of credit. On October 1, 2013, the Company borrowed an additional $440.0 million under its Second Amended Credit Facility, resulting in total outstanding indebtedness under the Second Amended Credit Facility of $605.2 million and an unused borrowing base capacity of $894.8 million. After the closing of the 2022 Notes and the West Williston Acquisition, the Lenders kept the borrowing base of the Second Amended Credit Facility at $1,500.0 million.
	Drilling contracts. In October 2013, the Company assumed an additional long-term drilling rig contract as part of the West Williston Acquisition. In the event of early termination under this contract, the Company would be obligated to pay an additional maximum amount of approximately $9.7 million if terminated immediately after execution.
	Purchase agreements. In October 2013, the Company entered into an agreement to purchase well fracturing equipment. The future obligation under this agreement is $3.6 million.

Organization_and_Operations_of1

Organization and Operations of the Company (Policies)	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Organization	'
	Organization
	Oasis Petroleum Inc. (together with its subsidiaries, “Oasis” or the “Company”) was formed on February 25, 2010, pursuant to the laws of the State of Delaware, to become a holding company for Oasis Petroleum LLC (“OP LLC”), the Company’s predecessor, which was formed as a Delaware limited liability company on February 26, 2007. In connection with its initial public offering in June 2010 and related corporate reorganization, the Company acquired all of the outstanding membership interests in OP LLC in exchange for shares of the Company’s common stock. In 2007, Oasis Petroleum North America LLC (“OPNA”), a Delaware limited liability company, was formed to conduct domestic oil and natural gas exploration and production activities. In 2008, Oasis Petroleum International LLC (“OPI”), a Delaware limited liability company, was formed to conduct business development activities outside of the United States of America. As of September 30, 2013, OPI had no business activities or material assets. In 2011, the Company formed Oasis Well Services LLC (“OWS”), a Delaware limited liability company, to provide well services to OPNA, and Oasis Petroleum Marketing LLC (“OPM”), a Delaware limited liability company, to provide marketing services to OPNA. In 2013, the Company formed Oasis Midstream Services LLC (“OMS”), a Delaware limited liability company, to provide midstream services to OPNA. As part of the formation of OMS, the Company transferred substantially all of its salt water disposal and other midstream assets from OPNA to OMS.
Basis of Presentation	'
	Basis of Presentation
	The accompanying condensed consolidated financial statements of the Company include the accounts of Oasis and its wholly owned subsidiaries. The accompanying condensed consolidated financial statements of the Company have not been audited by the Company’s independent registered public accounting firm, except that the Condensed Consolidated Balance Sheet at December 31, 2012 is derived from audited financial statements. All significant intercompany transactions have been eliminated in consolidation. Certain reclassifications of prior year balances have been made to conform such amounts to current year classifications. These reclassifications have no impact on net income. In the opinion of management, all adjustments, consisting of normal recurring adjustments necessary for the fair presentation, have been included. In preparing the accompanying condensed consolidated financial statements, management has made certain estimates and assumptions that affect reported amounts in the condensed consolidated financial statements and disclosures of contingencies. Actual results may differ from those estimates. The results for interim periods are not necessarily indicative of annual results.
	These interim financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain disclosures have been condensed or omitted from these financial statements. Accordingly, they do not include all of the information and notes required by accounting principles generally accepted in the United States of America (“GAAP”) for complete consolidated financial statements and should be read in conjunction with the Company’s audited consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012 (“2012 Annual Report”).
Significant Accounting Policies	'
	Significant Accounting Policies
	There have been no material changes to the Company’s critical accounting policies and estimates from those disclosed in the 2012 Annual Report other than those noted below.
Restricted Cash	'
	Restricted Cash
	Restricted cash represents aggregate net proceeds from the issuance of $1,000.0 million of 6.875% senior unsecured notes due 2022, which were held in escrow as of September 30, 2013 pending the closing of the acquisition of oil and gas properties in the Company’s West Williston project area (see Note 7 – Long-Term Debt and Note 15 – Subsequent Events). If the acquisition had not closed prior to December 12, 2013, the Company would have been required to use the restricted cash to redeem all of the notes due 2022 at a redemption price equal to 100% of the initial offering price, plus accrued and unpaid interest through the date of redemption.

Inventory_Tables

Inventory (Tables)	9 Months Ended
	Sep. 30, 2013
Inventory Disclosure [Abstract]	'
Schedule of Inventory	'
	Inventory consists of the following:
		September 30,		December 31,
		2013		2012
		(In thousands)
	Equipment and materials	$	12,498	$	16,438
	Crude oil inventory	5,860		4,269
	Total inventory	$	18,358	$	20,707

Property_Plant_and_Equipment_T

Property, Plant and Equipment (Tables)	9 Months Ended
	Sep. 30, 2013
Property, Plant and Equipment [Abstract]	'
Schedule of Property, Plant and Equipment	'
	The following table sets forth the Company’s property, plant and equipment:
		30-Sep-13			31-Dec-12
		(In thousands)
	Proved oil and gas properties (1)	$	2,916,453		$	2,271,711
	Less: Accumulated depreciation, depletion, amortization and impairment	(568,567		)	(383,564		)
	Proved oil and gas properties, net (2)	2,347,886			1,888,147
	Unproved oil and gas properties	128,062			76,417
	Total oil and gas properties, net	2,475,948			1,964,564
	Other property and equipment	157,926			49,732
	Less: Accumulated depreciation	(20,606		)	(7,696		)
	Other property and equipment, net (2)	137,320			42,036
	Total property, plant and equipment, net	$	2,613,268		$	2,006,600
	__________________
	-1	Included in the Company’s proved oil and gas properties are estimates of future asset retirement costs of $24.0 million and $20.7 million at September 30, 2013 and December 31, 2012, respectively.
	-2	The Company reclassed substantially all of its salt water disposal and other midstream assets from proved oil and gas properties to other property and equipment, effective January 1, 2013.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'
Hierarchy of Fair Value, Assets and Liabilities Measured on Recurring Basis	'
	The following tables set forth by level within the fair value hierarchy the Company’s financial assets and liabilities that were accounted for at fair value on a recurring basis:
		At fair value as of September 30, 2013
		Level 1		Level 2		Level 3		Total
		(In thousands)
	Assets:
	Money market funds	$	11,274	$	—	$	—	$	11,274
	Commodity derivative instruments (see Note 6)	—		3,779		—		3,779
	Total assets	$	11,274	$	3,779	$	—	$	15,053
	Liabilities:
	Commodity derivative instruments (see Note 6)	$	—	$	17,912	$	—	$	17,912
	Total liabilities	$	—	$	17,912	$	—	$	17,912
		At fair value as of December 31, 2012
		Level 1		Level 2		Level 3		Total
		(In thousands)
	Assets:
	Money market funds	$	66,387	$	—	$	—	$	66,387
	Commodity derivative instruments (see Note 6)	—		23,997		—		23,997
	Total assets	$	66,387	$	23,997	$	—	$	90,384
	Liabilities:
	Commodity derivative instruments (see Note 6)	$	—	$	1,428	$	—	$	1,428
	Total liabilities	$	—	$	1,428	$	—	$	1,428

Derivative_Instruments_Tables

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Schedule of Outstanding Commodity Derivative Instruments	'
	As of September 30, 2013, the Company had the following outstanding commodity derivative instruments, all of which settle monthly based on the average WTI crude oil index price:
	Settlement		Derivative		Total Notional			Weighted Average Prices											Fair Value
	Period		Instrument		Amount of Oil														Asset
								Swap				Sub-Floor			Floor		Ceiling		(Liability)
					(Barrels)			($/Barrel)											(In thousands)
	2013		Two-way collars		836,000										$	92.11	$	103.45	$	(2,636	)
	2013		Three-way collars		832,330							$	67.63		92.01		110.97		(118		)
	2013		Put spreads		168,670							70.89			90.89				4
	2013		Swaps		880,500			$	97.29										(5,118		)
	2014		Two-way collars		1,510,000										90.77		102.06		(159		)
	2014		Three-way collars		3,530,530							70.3			90.65		105.64		2,497
	2014		Put spreads		11,470							70			90				10
	2014		Swaps		2,218,500			95.87											(2,486		)
	2014		Swaps with sub-floors		2,004,000			92.6				70							(7,202		)
	2015		Two-way collars		108,500										90		99.86		284
	2015		Three-way collars		263,500							70.59			90.59		105.25		723
	2015		Swaps		108,500			93.07											148
	2015		Swaps with sub-floors		186,000			92.6				70							(80		)
																			$	(14,133	)
Schedule of Location and Fair Value of Outstanding Commodity Derivative Instruments	'
	The following table summarizes the location and fair value of all outstanding commodity derivative instruments recorded in the balance sheet for the periods presented:
	Fair Value of Derivative Instrument Assets (Liabilities)
				Fair Value
	Commodity	Balance Sheet Location		September 30,				31-Dec-12
				2013
				(In thousands)
	Crude oil	Derivative instruments — current assets		$	374			$	19,016
	Crude oil	Derivative instruments — non-current assets		3,405				4,981
	Crude oil	Derivative instruments — current liabilities		(17,060		)		(1,048		)
	Crude oil	Derivative instruments — non-current liabilities		(852		)		(380		)
	Total derivative instruments			$	(14,133	)		$	22,569
Realized and Unrealized Gains and Losses from Commodity Derivative Instruments	'
	The following table summarizes the location and amounts of gains and losses from the Company’s commodity derivative instruments for the periods presented:
				Three Months Ended								Nine Months Ended September 30,
				September 30,
		Income Statement Location		2013				2012				2013			2012
				(In thousands)
	Change in fair value of derivative instruments	Net gain (loss) on derivative instruments		$	(31,750	)		$	(27,690	)		$	(36,703	)	$	30,784
	Derivative settlements	Net gain (loss) on derivative instruments		(8,067		)		5,249				(5,135		)	2,784
	Total net gain (loss) on derivative instruments			$	(39,817	)		$	(22,441	)		$	(41,838	)	$	33,568
Summary of Gross and Net Information about Commodity Derivative Instruments	'
	The following tables summarize gross and net information about the Company’s commodity derivative instruments for the periods presented:
	Offsetting of Derivative Assets		Gross Amounts of Recognized Assets				Gross Amounts Offset				Net Amounts of Assets Presented
							in the Balance Sheet				in the Balance Sheet
			(In thousands)
	As of September 30, 2013		$	32,895			$	(29,116	)		$	3,779
	As of December 31, 2012		68,970				(44,973		)		23,997
	Offsetting of Derivative Liabilities		Gross Amounts of Recognized Liabilities				Gross Amounts Offset				Net Amounts of Liabilities Presented
							in the Balance Sheet				in the Balance Sheet
			(In thousands)
	As of September 30, 2013		$	47,028			$	(29,116	)		$	17,912
	As of December 31, 2012		46,401				(44,973		)		1,428

LongTerm_Debt_Tables

Long-Term Debt (Tables)	9 Months Ended
	Sep. 30, 2013
Debt Disclosure [Abstract]	'
Schedule of Long-Term Debt Interest Rate	'
	As of September 30, 2013, any outstanding LIBOR and ABR loans bore their respective interest rates plus the applicable margin indicated in the following table:
	Ratio of Total Outstanding Borrowings to Borrowing Base	Applicable Margin		Applicable Margin
		for LIBOR Loans		for ABR Loans
	Less than .25 to 1	1.5	%	0	%
	Greater than or equal to .25 to 1 but less than .50 to 1	1.75	%	0.25	%
	Greater than or equal to .50 to 1 but less than .75 to 1	2	%	0.5	%
	Greater than or equal to .75 to 1 but less than .90 to 1	2.25	%	0.75	%
	Greater than .90 to 1 but less than or equal 1	2.5	%	1	%

Asset_Retirement_Obligations_T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 2013
Asset Retirement Obligation Disclosure [Abstract]	'
Schedule of Changes in Asset Retirement Obligations	'
	The following table reflects the changes in the Company’s ARO during the nine months ended September 30, 2013:
		(In thousands)
	Balance at December 31, 2012	$	23,234
	Liabilities incurred during period	3,066
	Liabilities settled during period	23
	Accretion expense during period (1)	895
	Revisions to estimates	213
	Balance at September 30, 2013	$	27,431
	___________________
	-1	Included in depreciation, depletion and amortization on the Company’s Condensed Consolidated Statement of Operations.

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Summary of Performance Share Units	'
	The following table summarizes PSUs held by the Company’s officers at September 30, 2013:
		PSUs		Weighted Average
				Grant Date Fair Value
				per Unit
	Non-vested PSUs at December 31, 2012	155,220		$	26.22
	Granted	135,620		42.01
	Vested	—		—
	Forfeited	(21,540	)	32.89
	Non-vested PSUs at September 30, 2013	269,300		$	33.64
Summary of Assumptions	'
	The following assumptions were used for the Monte Carlo model to determine the grant date fair value and associated stock-based compensation expense of the PSUs granted:
		2013 Grants		2012 Grants
	Forecast period (years)	4		4.01
	Risk-free rate	0.65	%	0.46	%
	Oasis volatility	47.48	%	51	%

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Schedule of Weighted-Average Number of Shares Outstanding	'
	The following is a calculation of the basic and diluted weighted-average shares outstanding for the three and nine months ended September 30, 2013 and 2012:
		Three Months Ended		Nine Months Ended September 30,
		September 30,
		2013	2012	2013	2012
		(In thousands)
	Basic weighted average common shares outstanding	92,449	92,186	92,408	92,164
	Dilution effect of stock awards at end of period	387	230	430	179
	Diluted weighted average common shares outstanding	92,836	92,416	92,838	92,343
	Anti-dilutive stock-based compensation awards	789	748	719	541

Business_Segment_Information_T

Business Segment Information (Tables)	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]	'
Summarized Financial Information of Segments	'
	Summarized financial information for the Company’s segments is shown in the following table:
		Exploration and			Well Services			Midstream Services			Consolidated
		Production
		(In thousands)
	Three Months Ended September 30, 2013:
	Revenues	$	286,952		$	57,116		$	7,597		$	351,665
	Inter-segment revenues	—			(40,026		)	(6,141		)	(46,167		)
	Total revenues	286,952			17,090			1,456			305,498
	Operating income	140,765			5,870			4,227			150,862
	Other income (expense)	(62,628		)	(20		)	—			(62,648		)
	Income before income taxes	78,137			5,850			4,227			88,214
	Three Months Ended September 30, 2012:
	Revenues	$	178,748		$	37,160		$	—		$	215,908
	Inter-segment revenues	—			(31,197		)	—			(31,197		)
	Total revenues	178,748			5,963			—			184,711
	Operating income (loss)	89,279			(17,241		)	—			72,038
	Other income (expense)	(42,273		)	—			—			(42,273		)
	Income (loss) before income taxes	47,006			(17,241		)	—			29,765
	Nine Months Ended September 30, 2013:
	Revenues	$	770,445		$	124,266		$	19,451		$	914,162
	Inter-segment revenues	—			(90,000		)	(15,778		)	(105,778		)
	Total revenues	770,445			34,266			3,673			808,384
	Operating income	359,121			11,744			11,400			382,265
	Other income (expense)	(106,159		)	(11		)	—			(106,170		)
	Income before income taxes	252,962			11,733			11,400			276,095
	Nine Months Ended September 30, 2012:
	Revenues	$	461,857		$	54,909		$	—		$	516,766
	Inter-segment revenues	—			(44,425		)	—			(44,425		)
	Total revenues	461,857			10,484			—			472,341
	Operating income	190,257			116			—			190,373
	Other income (expense)	(12,863		)	—			—			(12,863		)
	Income before income taxes	177,394			116			—			177,510
	Total Assets:
	As of September 30, 2013	$	3,916,554		$	68,869		$	97,960		$	4,083,383
	As of December 31, 2012	2,475,820			52,974			—			2,528,794

Condensed_Consolidating_Financ1

Condensed Consolidating Financial Information (Tables)	9 Months Ended
	Sep. 30, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Condensed Consolidating Balance Sheet	'
	Condensed Consolidating Balance Sheet
	(In thousands, except share data)
		30-Sep-13
		Parent/			Combined			Intercompany			Consolidated
		Issuer			Guarantor			Eliminations
					Subsidiaries
	ASSETS
	Current assets
	Cash and cash equivalents	$	32,955		$	92,485		$	—		$	125,440
	Restricted cash	986,210			—			—			986,210
	Accounts receivable – oil and gas revenues	—			155,068			—			155,068
	Accounts receivable – joint interest partners	—			120,058			—			120,058
	Accounts receivable – from affiliates	770			8,432			(9,202		)	—
	Inventory	—			18,358			—			18,358
	Prepaid expenses	477			6,963			—			7,440
	Advances to joint interest partners	—			1,170			—			1,170
	Derivative instruments	—			374			—			374
	Deferred income taxes	—			8,683			—			8,683
	Other current assets	2			471			—			473
	Total current assets	1,020,414			412,062			(9,202		)	1,423,274
	Property, plant and equipment
	Oil and gas properties (successful efforts method)	—			3,044,515			—			3,044,515
	Other property and equipment	—			157,926			—			157,926
	Less: accumulated depreciation, depletion, amortization and impairment	—			(589,173		)	—			(589,173		)
	Total property, plant and equipment, net	—			2,613,268			—			2,613,268
	Investments in and advances to subsidiaries	2,082,828			—			(2,082,828		)	—
	Derivative instruments	—			3,405			—			3,405
	Deferred income taxes	69,795			—			(69,795		)	—
	Deferred costs and other assets	34,128			9,308			—			43,436
	Total assets	$	3,207,165		$	3,038,043		$	(2,161,825	)	$	4,083,383
	LIABILITIES AND STOCKHOLDERS’ EQUITY
	Current liabilities
	Accounts payable	$	—		$	39,468		$	—		$	39,468
	Accounts payable – from affiliates	8,432			770			(9,202		)	—
	Advances from joint interest partners	—			13,211			—			13,211
	Revenues and production taxes payable	—			133,083			—			133,083
	Accrued liabilities	46			198,447			—			198,493
	Accrued interest payable	22,809			64			—			22,873
	Derivative instruments	—			17,060			—			17,060
	Total current liabilities	31,287			402,103			(9,202		)	424,188
	Long-term debt	2,200,000			160,000			—			2,360,000
	Asset retirement obligations	—			26,999			—			26,999
	Derivative instruments	—			852			—			852
	Deferred income taxes	—			362,951			(69,795		)	293,156
	Other liabilities	—			2,310			—			2,310
	Total liabilities	2,231,287			955,215			(78,997		)	3,107,505
	Stockholders’ equity
	Capital contributions from affiliates	—			1,643,729			(1,643,729		)	—
	Common stock, $0.01 par value; 300,000,000 shares authorized; 93,854,867 issued and 93,690,494 outstanding	926			—			—			926
	Treasury stock, at cost; 164,373 shares	(5,220		)	—			—			(5,220		)
	Additional paid-in-capital	666,770			8,743			(8,743		)	666,770
	Retained earnings	313,402			430,356			(430,356		)	313,402
	Total stockholders’ equity	975,878			2,082,828			(2,082,828		)	975,878
	Total liabilities and stockholders’ equity	$	3,207,165		$	3,038,043		$	(2,161,825	)	$	4,083,383
		31-Dec-12
		Parent/			Combined			Intercompany			Consolidated
		Issuer			Guarantor			Eliminations
					Subsidiaries
	ASSETS
	Current assets
	Cash and cash equivalents	$	133,797		$	79,650		$	—		$	213,447
	Short-term investments	25,891			—			—			25,891
	Accounts receivable – oil and gas revenues	—			110,341			—			110,341
Accounts receivable – joint interest partners	—			99,194			—			99,194
Accounts receivable – from affiliates	310			5,845			(6,155		)	—
Inventory	—			20,707			—			20,707
Prepaid expenses	313			1,457			—			1,770
Advances to joint interest partners	—			1,985			—			1,985
Derivative instruments	—			19,016			—			19,016
Other current assets	235			100			—			335
Total current assets	160,546			338,295			(6,155		)	492,686
Property, plant and equipment
Oil and gas properties (successful efforts method)	—			2,348,128			—			2,348,128
Other property and equipment	—			49,732			—			49,732
Less: accumulated depreciation, depletion, amortization and impairment	—			(391,260		)	—			(391,260		)
Total property, plant and equipment, net	—			2,006,600			—			2,006,600
Investments in and advances to subsidiaries	1,807,010			—			(1,807,010		)	—
Derivative instruments	—			4,981			—			4,981
Deferred income taxes	42,746			—			(42,746		)	—
Deferred costs and other assets	20,748			3,779			—			24,527
Total assets	$	2,031,050		$	2,353,655		$	(1,855,911	)	$	2,528,794
LIABILITIES AND STOCKHOLDERS’ EQUITY
Current liabilities
Accounts payable	$	9		$	12,482		$	—		$	12,491
Accounts payable – from affiliates	5,845			310			(6,155		)	—
Advances from joint interest partners	—			21,176			—			21,176
Revenues and production taxes payable	—			71,553			—			71,553
Accrued liabilities	100			189,763			—			189,863
Accrued interest payable	30,091			5			—			30,096
Derivative instruments	—			1,048			—			1,048
Deferred income taxes	—			4,558			—			4,558
Total current liabilities	36,045			300,895			(6,155		)	330,785
Long-term debt	1,200,000			—			—			1,200,000
Asset retirement obligations	—			22,956			—			22,956
Derivative instruments	—			380			—			380
Deferred income taxes	—			220,417			(42,746		)	177,671
Other liabilities	—			1,997			—			1,997
Total liabilities	1,236,045			546,645			(48,901		)	1,733,789
Stockholders’ equity
Capital contributions from affiliates	—			1,586,780			(1,586,780		)	—
Common stock, $0.01 par value; 300,000,000 shares authorized; 93,432,712 issued and 93,303,298 outstanding	925			—			—			925
Treasury stock, at cost; 129,414 shares	(3,796		)	—			—			(3,796		)
Additional paid-in-capital	657,943			8,743			(8,743		)	657,943
Retained earnings	139,933			211,487			(211,487		)	139,933
Total stockholders’ equity	795,005			1,807,010			(1,807,010		)	795,005
Total liabilities and stockholders’ equity	$	2,031,050		$	2,353,655		$	(1,855,911	)	$	2,528,794
Condensed Consolidating Statement of Operations	'
	Condensed Consolidating Statement of Operations
	(In thousands)
		Three Months Ended September 30, 2013
		Parent/			Combined			Intercompany			Consolidated
		Issuer			Guarantor			Eliminations
					Subsidiaries
	Revenues
	Oil and gas revenues	$	—		$	286,952		$	—		$	286,952
	Well services and midstream revenues	—			18,546			—			18,546
	Total revenues	—			305,498			—			305,498
	Expenses
	Lease operating expenses	—			21,831			—			21,831
	Well services and midstream operating expenses	—			10,319			—			10,319
	Marketing, transportation and gathering expenses	—			5,688			—			5,688
	Production taxes	—			26,823			—			26,823
	Depreciation, depletion and amortization	—			72,728			—			72,728
	Exploration expenses	—			463			—			463
	Impairment of oil and gas properties	—			56			—			56
	General and administrative expenses	3,746			12,982			—			16,728
	Total expenses	3,746			150,890			—			154,636
	Operating income (loss)	(3,746		)	154,608			—			150,862
	Other income (expense)
	Equity in earnings in subsidiaries	70,118			—			(70,118		)	—
	Net loss on derivative instruments	—			(39,817		)	—			(39,817		)
	Interest expense, net of capitalized interest	(21,277		)	(1,577		)	—			(22,854		)
	Other income	15			8			—			23
	Total other income (expense)	48,856			(41,386		)	(70,118		)	(62,648		)
	Income before income taxes	45,110			113,222			(70,118		)	88,214
	Income tax benefit (expense)	9,389			(43,104		)	—			(33,715		)
	Net income	$	54,499		$	70,118		$	(70,118	)	$	54,499
	Condensed Consolidating Statement of Operations
	(In thousands)
		Three Months Ended September 30, 2012
		Parent/			Combined			Intercompany			Consolidated
		Issuer			Guarantor			Eliminations
					Subsidiaries
	Revenues
	Oil and gas revenues	$	—		$	178,748		$	—		$	178,748
	Well services revenues	—			5,963			—			5,963
	Total revenues	—			184,711			—			184,711
	Expenses
	Lease operating expenses	—			16,134			—			16,134
	Well services operating expenses	—			5,420			—			5,420
	Marketing, transportation and gathering expenses	—			2,744			—			2,744
	Production taxes	—			16,433			—			16,433
	Depreciation, depletion and amortization	—			57,684			—			57,684
	Exploration expenses	—			336			—			336
	Impairment of oil and gas properties	—			36			—			36
	General and administrative expenses	2,988			10,898			—			13,886
	Total expenses	2,988			109,685			—			112,673
	Operating income (loss)	(2,988		)	75,026			—			72,038
	Other income (expense)
	Equity in earnings in subsidiaries	32,735			—			(32,735		)	—
	Net loss on derivative instruments	—			(22,441		)	—			(22,441		)
	Interest expense, net of capitalized interest	(20,307		)	(672		)	—			(20,979		)
	Other income	238			909			—			1,147
	Total other income (expense)	12,666			(22,204		)	(32,735		)	(42,273		)
	Income before income taxes	9,678			52,822			(32,735		)	29,765
	Income tax benefit (expense)	8,636			(20,087		)	—			(11,451		)
	Net income	$	18,314		$	32,735		$	(32,735	)	$	18,314
	Condensed Consolidating Statement of Operations
	(In thousands)
		Nine Months Ended September 30, 2013
	Parent/			Combined			Intercompany			Consolidated
	Issuer			Guarantor			Eliminations
				Subsidiaries
Revenues
Oil and gas revenues	$	—		$	770,445		$	—		$	770,445
Well services and midstream revenues	—			37,939			—			37,939
Total revenues	—			808,384			—			808,384
Expenses
Lease operating expenses	—			59,586			—			59,586
Well services and midstream operating expenses	—			19,877			—			19,877
Marketing, transportation and gathering expenses	—			19,856			—			19,856
Production taxes	—			70,309			—			70,309
Depreciation, depletion and amortization	—			205,779			—			205,779
Exploration expenses	—			2,712			—			2,712
Impairment of oil and gas properties	—			762			—			762
General and administrative expenses	10,146			37,092			—			47,238
Total expenses	10,146			415,973			—			426,119
Operating income (loss)	(10,146		)	392,411			—			382,265
Other income (expense)
Equity in earnings in subsidiaries	218,869			—			(218,869		)	—
Net loss on derivative instruments	—			(41,838		)	—			(41,838		)
Interest expense, net of capitalized interest	(61,955		)	(3,474		)	—			(65,429		)
Other income	(348		)	1,445			—			1,097
Total other income (expense)	156,566			(43,867		)	(218,869		)	(106,170		)
Income before income taxes	146,420			348,544			(218,869		)	276,095
Income tax benefit (expense)	27,049			(129,675		)	—			(102,626		)
Net income	$	173,469		$	218,869		$	(218,869	)	$	173,469
Condensed Consolidating Statement of Operations
(In thousands)
	Nine Months Ended September 30, 2012
	Parent/			Combined			Intercompany			Consolidated
	Issuer			Guarantor			Eliminations
				Subsidiaries
Revenues
Oil and gas revenues	$	—		$	461,857		$	—		$	461,857
Well services and midstream revenues	—			10,484			—			10,484
Total revenues	—			472,341			—			472,341
Expenses
Lease operating expenses	—			37,979			—			37,979
Well services and midstream operating expenses	—			7,104			—			7,104
Marketing, transportation and gathering expenses	—			7,283			—			7,283
Production taxes	—			43,419			—			43,419
Depreciation, depletion and amortization	—			140,783			—			140,783
Exploration expenses	—			3,171			—			3,171
Impairment of oil and gas properties	—			2,607			—			2,607
General and administrative expenses	8,078			31,544			—			39,622
Total expenses	8,078			273,890			—			281,968
Operating income (loss)	(8,078		)	198,451			—			190,373
Other income (expense)
Equity in earnings in subsidiaries	145,021			—			(145,021		)	—
Net gain on derivative instruments	—			33,568			—			33,568
Interest expense, net of capitalized interest	(47,136		)	(1,816		)	—			(48,952		)
Other income	533			1,988			—			2,521
Total other income (expense)	98,418			33,740			(145,021		)	(12,863		)
Income before income taxes	90,340			232,191			(145,021		)	177,510
Income tax benefit (expense)	20,458			(87,170		)	—			(66,712		)
Net income	$	110,798		$	145,021		$	(145,021	)	$	110,798
Condensed Consolidating Statement of Cash Flows	'
	Condensed Consolidating Statement of Cash Flows
	(In thousands)
		Nine Months Ended September 30, 2013
		Parent/			Combined			Intercompany			Consolidated
		Issuer			Guarantor			Eliminations
					Subsidiaries
	Cash flows from operating activities:
	Net income	$	173,469		$	218,869		$	(218,869	)	$	173,469
	Adjustments to reconcile net income to net cash provided by (used in) operating activities:
	Equity in earnings of subsidiaries	(218,869		)	—			218,869			—
	Depreciation, depletion and amortization	—			205,779			—			205,779
	Impairment of oil and gas properties	—			762			—			762
	Deferred income taxes	(27,049		)	129,293			—			102,244
	Derivative instruments	—			41,838			—			41,838
	Stock-based compensation expenses	8,196			215			—			8,411
	Debt discount amortization and other	2,850			(157		)	—			2,693
	Working capital and other changes:
	Change in accounts receivable	(460		)	(69,614		)	2,587			(67,487		)
	Change in inventory	—			(8,820		)	—			(8,820		)
	Change in prepaid expenses	(164		)	(5,011		)	—			(5,175		)
	Change in other current assets	233			(371		)	—			(138		)
	Change in other assets	—			(63		)	—			(63		)
	Change in accounts payable and accrued liabilities	(4,758		)	89,591			(2,587		)	82,246
	Change in other current liabilities	—			—			—			—
	Change in other liabilities	—			922			—			922
	Net cash provided by (used in) operating activities	(66,552		)	603,233			—			536,681
	Cash flows from investing activities:
	Capital expenditures	—			(654,175		)	—			(654,175		)
	Acquisitions of oil and gas properties	—			(133,061		)	—			(133,061		)
	Increase in restricted cash	(986,210		)	—			—			(986,210		)
	Derivative settlements	—			(5,135		)	—			(5,135		)
	Redemptions of short-term investments	25,000			—			—			25,000
	Advances from joint interest partners	—			(7,965		)	—			(7,965		)
	Net cash used in investing activities	(961,210		)	(800,336		)	—			(1,761,546		)
	Cash flows from financing activities:
	Proceeds from credit facility	—			160,000			—			160,000
	Proceeds from issuance of senior notes	1,000,000			—			—			1,000,000
	Purchases of treasury stock	(1,424		)	—			—			(1,424		)
	Debt issuance costs	(15,340		)	(6,378		)	—			(21,718		)
	Investment in / capital contributions from affiliates	(56,316		)	56,316			—			—
	Net cash provided by financing activities	926,920			209,938			—			1,136,858
	Increase (decrease) in cash and cash equivalents	(100,842		)	12,835			—			(88,007		)
	Cash and cash equivalents at beginning of period	133,797			79,650			—			213,447
	Cash and cash equivalents at end of period	$	32,955		$	92,485		$	—		$	125,440
	Condensed Consolidating Statement of Cash Flows
	(In thousands)
		Nine Months Ended September 30, 2012
		Parent/			Combined			Intercompany			Consolidated
		Issuer			Guarantor			Eliminations
					Subsidiaries
	Cash flows from operating activities:
	Net income	$	110,798		$	145,021		$	(145,021	)	$	110,798
	Adjustments to reconcile net income to net cash provided by operating activities:
	Equity in earnings of subsidiaries	(145,021		)	—			145,021			—
	Depreciation, depletion and amortization	—			140,783			—			140,783
	Impairment of oil and gas properties	—			2,607			—			2,607
	Deferred income taxes	(20,458		)	87,106			—			66,648
	Derivative instruments	—			(33,568		)	—			(33,568		)
	Stock-based compensation expenses	6,397			230			—			6,627
	Debt discount amortization and other	1,616			422			—			2,038
	Working capital and other changes:
	Change in accounts receivable	(203		)	(70,899		)	1,939			(69,163		)
	Change in inventory	—			(26,790		)	—			(26,790		)
Change in prepaid expenses	(192		)	(1,817		)	—			(2,009		)
Change in other current assets	(60		)	473			—			413
Change in other assets	(24		)	(95		)	—			(119		)
Change in accounts payable and accrued liabilities	8,620			72,398			(1,939		)	79,079
Change in other current liabilities	—			4,784			—			4,784
Net cash provided by operating activities	(38,527		)	320,655			—			282,128
Cash flows from investing activities:
Capital expenditures	—			(777,516		)	—			(777,516		)
Derivative settlements	—			2,784			—			2,784
Purchases of short-term investments	(126,213		)	—			—			(126,213		)
Redemptions of short-term investments	19,994			—			—			19,994
Advances from joint interest partners	—			17,508			—			17,508
Net cash used in investing activities	(106,219		)	(757,224		)	—			(863,443		)
Cash flows from financing activities:
Proceeds from issuance of senior notes	400,000			—						400,000
Purchases of treasury stock	(1,299		)	—			—			(1,299		)
Debt issuance costs	(7,255		)	(700		)	—			(7,955		)
Investment in / capital contributions from affiliates	(459,012		)	459,012			—			—
Net cash provided by (used in) financing activities	(67,566		)	458,312			—			390,746
Increase (decrease) in cash and cash equivalents	(212,312		)	21,743			—			(190,569		)
Cash and cash equivalents at beginning of period	443,482			27,390			—			470,872
Cash and cash equivalents at end of period	$	231,170		$	49,133		$	—		$	280,303

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Details) (Senior Unsecured Debt [Member], 2022 Notes [Member], USD $)	0 Months Ended
	Sep. 24, 2013
Senior Unsecured Debt [Member] | 2022 Notes [Member]	'
Debt Instrument [Line Items]	'
Principal debt amount	$1,000,000,000
Stated interest rate	6.88%
Redemption price, percentage	100.00%

Inventory_Schedule_of_Inventor

Inventory - Schedule of Inventory (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Inventory Disclosure [Abstract]	'	'
Equipment and materials	$12,498	$16,438
Crude oil inventory	5,860	4,269
Total inventory	$18,358	$20,707

Property_Plant_and_Equipment_S

Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Detail) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified
Property, Plant and Equipment [Abstract]	'		'
Proved oil and gas properties	$2,916,453	[1]	$2,271,711	[1]
Less: Accumulated depreciation, depletion, amortization and impairment	-568,567		-383,564
Proved oil and gas properties, net	2,347,886	[2]	1,888,147	[2]
Unproved oil and gas properties	128,062		76,417
Total oil and gas properties, net	2,475,948		1,964,564
Other property and equipment	157,926		49,732
Less: Accumulated depreciation	-20,606		-7,696
Other property and equipment, net	137,320	[2]	42,036	[2]
Total property, plant and equipment, net	$2,613,268		$2,006,600
[1]	Included in the Company’s proved oil and gas properties are estimates of future asset retirement costs of $24.0 million and $20.7 million at September 30, 2013 and December 31, 2012, respectively.
[2]	The Company reclassed substantially all of its salt water disposal and other midstream assets from proved oil and gas properties to other property and equipment, effective January 1, 2013.

Property_Plant_and_Equipment_S1

Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Parenthetical) (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Property, Plant and Equipment [Abstract]	'	'
Asset retirement costs	$24	$20.70

Property_Plant_and_Equipment_A

Property, Plant and Equipment - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended		0 Months Ended	1 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 26, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 26, 2013	Sep. 30, 2013
						Unproved property leases [Member]	Unproved property leases [Member]	Unproved property leases [Member]	Unproved property leases [Member]	East Nesson [Member]	West Williston Acquisition [Member]
										acre
Property, Plant and Equipment [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Impairment of oil and gas properties	$56,000	$36,000	$762,000	$2,607,000	'	$56,000	$36,000	$762,000	$2,607,000	'	'
Acres acquired	'	'	'	'	'	'	'	'	'	25,000	'
Payments to acquire productive assets	'	'	'	'	'	'	'	'	'	54,800,000	'
Investment commitment	7,200,000	'	7,200,000	'	8,200,000	'	'	'	'	'	'
Acquisition, consideration transferred, deposit	'	'	'	'	'	'	'	'	'	'	$72,500,000

Fair_Value_Measurements_Hierar

Fair Value Measurements - Hierarchy of Fair Value, Assets and Liabilities Measured on Recurring Basis (Detail) (Fair Value, Measurements, Recurring [Member], USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Assets:	'	'
Total assets	$15,053	$90,384
Liabilities:	'	'
Total liabilities	17,912	1,428
Money market funds [Member]	'	'
Assets:	'	'
Total assets	11,274	66,387
Commodity derivative instruments [Member]	'	'
Assets:	'	'
Total assets	3,779	23,997
Liabilities:	'	'
Total liabilities	17,912	1,428
Level 1 [Member]	'	'
Assets:	'	'
Total assets	11,274	66,387
Liabilities:	'	'
Total liabilities	'	'
Level 1 [Member] | Money market funds [Member]	'	'
Assets:	'	'
Total assets	11,274	66,387
Level 1 [Member] | Commodity derivative instruments [Member]	'	'
Assets:	'	'
Total assets	'	'
Liabilities:	'	'
Total liabilities	'	'
Level 2 [Member]	'	'
Assets:	'	'
Total assets	3,779	23,997
Liabilities:	'	'
Total liabilities	17,912	1,428
Level 2 [Member] | Money market funds [Member]	'	'
Assets:	'	'
Total assets	'	'
Level 2 [Member] | Commodity derivative instruments [Member]	'	'
Assets:	'	'
Total assets	3,779	23,997
Liabilities:	'	'
Total liabilities	17,912	1,428
Level 3 [Member]	'	'
Assets:	'	'
Total assets	'	'
Liabilities:	'	'
Total liabilities	'	'
Level 3 [Member] | Money market funds [Member]	'	'
Assets:	'	'
Total assets	'	'
Level 3 [Member] | Commodity derivative instruments [Member]	'	'
Assets:	'	'
Total assets	'	'
Liabilities:	'	'
Total liabilities	'	'

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Debt Instrument [Line Items]	'	'
Derivative credit risk valuation adjustment, derivative assets	$400,000	$29,000
Long-term debt	2,360,000,000	1,200,000,000
Asset retirement obligation, carrying value	27,431,000	23,234,000
Senior Unsecured Debt [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-term debt	2,200,000,000	'
Long-term debt, fair value	2,325,000,000	'
Second Amended Credit Facility [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-term debt	$160,000,000	'

Derivative_Instruments_Schedul

Derivative Instruments - Schedule of Outstanding Commodity Derivative Instruments (Detail) (USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified
Derivative [Line Items]	'
Fair Value Asset (Liability)	($14,133)
2013 Two-Way Collars [Member]	'
Derivative [Line Items]	'
Settlement Period	'2013
Total Notional Amount of Oil (Barrels)	836,000
Average Floor Price (in dollars per barrel)	92.11
Average Ceiling Price (in dollars per barrel)	103.45
Fair Value Asset (Liability)	-2,636
2013 Three-Way Collars [Member]	'
Derivative [Line Items]	'
Settlement Period	'2013
Total Notional Amount of Oil (Barrels)	832,330
Average Sub-Floor Price (in dollars per barrel)	67.63
Average Floor Price (in dollars per barrel)	92.01
Average Ceiling Price (in dollars per barrel)	110.97
Fair Value Asset (Liability)	-118
2013 Put Spreads [Member]	'
Derivative [Line Items]	'
Settlement Period	'2013
Total Notional Amount of Oil (Barrels)	168,670
Average Sub-Floor Price (in dollars per barrel)	70.89
Average Floor Price (in dollars per barrel)	90.89
Fair Value Asset (Liability)	4
2013 Swaps [Member]	'
Derivative [Line Items]	'
Settlement Period	'2013
Total Notional Amount of Oil (Barrels)	880,500
Average Swap Price (in dollars per barrel)	97.29
Fair Value Asset (Liability)	-5,118
2014 Two-Way Collars [Member]	'
Derivative [Line Items]	'
Settlement Period	'2014
Total Notional Amount of Oil (Barrels)	1,510,000
Average Floor Price (in dollars per barrel)	90.77
Average Ceiling Price (in dollars per barrel)	102.06
Fair Value Asset (Liability)	-159
2014 Three-Way Collars [Member]	'
Derivative [Line Items]	'
Settlement Period	'2014
Total Notional Amount of Oil (Barrels)	3,530,530
Average Sub-Floor Price (in dollars per barrel)	70.3
Average Floor Price (in dollars per barrel)	90.65
Average Ceiling Price (in dollars per barrel)	105.64
Fair Value Asset (Liability)	2,497
2014 Put Spreads [Member]	'
Derivative [Line Items]	'
Settlement Period	'2014
Total Notional Amount of Oil (Barrels)	11,470
Average Sub-Floor Price (in dollars per barrel)	70
Average Floor Price (in dollars per barrel)	90
Fair Value Asset (Liability)	10
2014 Swaps [Member]	'
Derivative [Line Items]	'
Settlement Period	'2014
Total Notional Amount of Oil (Barrels)	2,218,500
Average Swap Price (in dollars per barrel)	95.87
Fair Value Asset (Liability)	-2,486
2014 Swaps with sub-floors [Member]	'
Derivative [Line Items]	'
Settlement Period	'2014
Total Notional Amount of Oil (Barrels)	2,004,000
Average Swap Price (in dollars per barrel)	92.6
Average Sub-Floor Price (in dollars per barrel)	70
Fair Value Asset (Liability)	-7,202
2015 Two-Way Collars [Member]	'
Derivative [Line Items]	'
Settlement Period	'2015
Total Notional Amount of Oil (Barrels)	108,500
Average Floor Price (in dollars per barrel)	90
Average Ceiling Price (in dollars per barrel)	99.86
Fair Value Asset (Liability)	284
2015 Three-Way Collars [Member]	'
Derivative [Line Items]	'
Settlement Period	'2015
Total Notional Amount of Oil (Barrels)	263,500
Average Sub-Floor Price (in dollars per barrel)	70.59
Average Floor Price (in dollars per barrel)	90.59
Average Ceiling Price (in dollars per barrel)	105.25
Fair Value Asset (Liability)	723
2015 Swaps [Member]	'
Derivative [Line Items]	'
Settlement Period	'2015
Total Notional Amount of Oil (Barrels)	108,500
Average Swap Price (in dollars per barrel)	93.07
Fair Value Asset (Liability)	148
2015 Swaps with sub-floors [Member]	'
Derivative [Line Items]	'
Settlement Period	'2015
Total Notional Amount of Oil (Barrels)	186,000
Average Swap Price (in dollars per barrel)	92.6
Average Sub-Floor Price (in dollars per barrel)	70
Fair Value Asset (Liability)	($80)

Derivative_Instruments_Schedul1

Derivative Instruments - Schedule of Location and Fair Value of Outstanding Commodity Derivative Instruments (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Derivatives, Fair Value [Line Items]	'	'
Derivative instruments — current assets	$374	$19,016
Derivative instruments — non-current assets	3,405	4,981
Derivative instruments — current liabilities	-17,060	-1,048
Derivative instruments — non-current liabilities	-852	-380
Total derivative instruments	-14,133	'
Crude oil [Member]	'	'
Derivatives, Fair Value [Line Items]	'	'
Derivative instruments — current assets	374	19,016
Derivative instruments — non-current assets	3,405	4,981
Derivative instruments — current liabilities	-17,060	-1,048
Derivative instruments — non-current liabilities	-852	-380
Total derivative instruments	($14,133)	$22,569

Derivative_Instruments_Realize

Derivative Instruments - Realized and Unrealized Gains and Losses from Commodity Derivative Instruments (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'	'	'	'
Change in fair value of derivative instruments	($31,750)	($27,690)	($36,703)	$30,784
Derivative settlements	-8,067	5,249	-5,135	2,784
Total net gain (loss) on derivative instruments	($39,817)	($22,441)	($41,838)	$33,568

Derivative_Instruments_Summary

Derivative Instruments - Summary of Gross and Net Information about Commodity Derivative Instruments (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'	'
Gross Amounts of Recognized Assets	$32,895	$68,970
Derivative Assets, Gross Amounts Offset in the Balance Sheet	-29,116	-44,973
Net Amounts of Assets Presented in the Balance Sheet	3,779	23,997
Gross Amounts of Recognized Liabilities	47,028	46,401
Derivative Liabilities, Gross Amounts Offset in the Balance Sheet	-29,116	-44,973
Net Amounts of Liabilities Presented in the Balance Sheet	$17,912	$1,428

LongTerm_Debt_Additional_Infor

Long-Term Debt - Additional Information (Detail) (USD $)

3 Months Ended

9 Months Ended

24 Months Ended

9 Months Ended

9 Months Ended

0 Months Ended

12 Months Ended

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Apr. 05, 2013

Mar. 31, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 24, 2013

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2012

Oct. 02, 2013

Senior Unsecured Debt [Member]

Senior Unsecured Debt [Member]

Second Amended Credit Facility [Member]

Second Amended Credit Facility [Member]

Second Amended Credit Facility [Member]

Current Ratio [Member]

Minimum [Member]

2022 Notes [Member]

2019 Notes [Member]

2021 Notes [Member]

2023 Notes [Member]

Subsequent Event [Member]

Second Amended Credit Facility [Member]

Second Amended Credit Facility [Member]

Senior Unsecured Debt [Member]

Senior Unsecured Debt [Member]

Senior Unsecured Debt [Member]

Senior Unsecured Debt [Member]

Second Amended Credit Facility [Member]

Debt Disclosure [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Principal debt amount

'

'

'

'

'

'

'

'

'

'

'

$1,000,000,000

$400,000,000

$400,000,000

$400,000,000

'

Stated interest rate

'

'

'

'

'

'

'

'

'

'

'

6.88%

7.25%

6.50%

6.88%

'

Debt instrument, maturity date

'

'

'

'

'

'

5-Apr-18

'

'

'

'

15-Mar-22

1-Feb-19

1-Nov-21

15-Jan-23

'

Net proceeds from issuance of notes

'

'

'

'

'

1,175,800,000

'

'

'

'

'

983,000,000

'

'

'

'

Exchange term

'

'

'

'

'

'

'

'

'

'

'

'360 days

'

'

'

'

Exchange increase in interest rate

'

'

'

'

'

'

'

'

'

'

'

1.00%

'

'

'

'

Senior unsecured notes payment frequency

'

'

'

'

'semi-annually

'

'

'

'

'

'

'

'

'

'

'

Redemption percentage, maximum

'

'

'

'

35.00%

'

'

'

'

'

'

'

'

'

'

'

Redemption term

'

'

'

'

'180 days

'

'

'

'

'

'

'

'

'

'

'

Percentage of minimum outstanding principal amount

'

'

'

'

65.00%

'

'

'

'

'

'

'

'

'

'

'

Event of default by payment default ($10.0 million or more)

'

'

'

'

10,000,000

'

'

'

'

'

'

'

'

'

'

'

Event of default by final judgments (in excess of $10.0 million)

'

'

'

'

10,000,000

'

'

'

'

'

'

'

'

'

'

'

Line of credit facility, maximum borrowing capacity

'

'

'

'

'

'

'

1,250,000,000

750,000,000

'

'

'

'

'

'

1,500,000,000

Line of credit facility, current borrowing capacity

'

'

'

'

'

'

'

900,000,000

'

'

'

'

'

'

'

1,500,000,000

Line of credit facility, capacity available for specific purpose other than for trade purchases

'

'

'

'

'

'

'

2,500,000,000

1,000,000,000

'

'

'

'

'

'

'

Percentage of the reserve value of assets as determined by reserve reports (at least 80%)

'

'

'

'

'

'

80.00%

'

'

'

'

'

'

'

'

'

Commitment fee of borrowing base capacity not utilized

'

'

'

'

'

'

0.38%

'

'

'

'

'

'

'

'

'

Ratio of EBITDAX to interest expense necessary to maintain covenants

'

'

'

'

'

'

'

'

'

'

2.5

'

'

'

'

'

Minimum current ratio

'

'

'

'

'

'

'

'

'

1

'

'

'

'

'

'

Line of credit facility, amount outstanding

'

'

'

'

'

'

160,000,000

'

'

'

'

'

'

'

'

605,200,000

Outstanding letters of credit

'

'

'

'

'

'

5,200,000

'

'

'

'

'

'

'

'

'

Line of credit facility, remaining borrowing capacity

'

'

'

'

'

'

1,334,800,000

'

'

'

'

'

'

'

'

894,800,000

Weighted average interest rate

'

'

'

'

'

'

2.80%

'

'

'

'

'

'

'

'

'

Deferred financing costs

42,300,000

'

42,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Amortization of deferred financing costs

$1,000,000

$800,000

$2,900,000

$2,100,000

'

'

'

'

'

'

'

'

'

'

'

'

LongTerm_Debt_Schedule_of_Long

Long-Term Debt - Schedule of Long-Term Debt Interest Rate (Detail)	9 Months Ended
	Sep. 30, 2013
Less than .25 to 1 [Member] | Maximum [Member]	'
Debt Instrument [Line Items]	'
Ratio of Total Outstanding Borrowings to Borrowing Base	0.25
Less than .25 to 1 [Member] | LIBOR [Member]	'
Debt Instrument [Line Items]	'
Debt instrument interest rate terms, in percentage	1.50%
Less than .25 to 1 [Member] | ABR [Member]	'
Debt Instrument [Line Items]	'
Debt instrument interest rate terms, in percentage	0.00%
Greater than or equal to .25 to 1 but less than .50 to 1 [Member] | Maximum [Member]	'
Debt Instrument [Line Items]	'
Ratio of Total Outstanding Borrowings to Borrowing Base	0.5
Greater than or equal to .25 to 1 but less than .50 to 1 [Member] | Minimum [Member]	'
Debt Instrument [Line Items]	'
Ratio of Total Outstanding Borrowings to Borrowing Base	0.25
Greater than or equal to .25 to 1 but less than .50 to 1 [Member] | LIBOR [Member]	'
Debt Instrument [Line Items]	'
Debt instrument interest rate terms, in percentage	1.75%
Greater than or equal to .25 to 1 but less than .50 to 1 [Member] | ABR [Member]	'
Debt Instrument [Line Items]	'
Debt instrument interest rate terms, in percentage	0.25%
Greater than or equal to .50 to 1 but less than .75 to 1 [Member] | Maximum [Member]	'
Debt Instrument [Line Items]	'
Ratio of Total Outstanding Borrowings to Borrowing Base	0.75
Greater than or equal to .50 to 1 but less than .75 to 1 [Member] | Minimum [Member]	'
Debt Instrument [Line Items]	'
Ratio of Total Outstanding Borrowings to Borrowing Base	0.5
Greater than or equal to .50 to 1 but less than .75 to 1 [Member] | LIBOR [Member]	'
Debt Instrument [Line Items]	'
Debt instrument interest rate terms, in percentage	2.00%
Greater than or equal to .50 to 1 but less than .75 to 1 [Member] | ABR [Member]	'
Debt Instrument [Line Items]	'
Debt instrument interest rate terms, in percentage	0.50%
Greater than or equal to .75 to 1 but less than .90 to 1 [Member] | Maximum [Member]	'
Debt Instrument [Line Items]	'
Ratio of Total Outstanding Borrowings to Borrowing Base	0.9
Greater than or equal to .75 to 1 but less than .90 to 1 [Member] | Minimum [Member]	'
Debt Instrument [Line Items]	'
Ratio of Total Outstanding Borrowings to Borrowing Base	0.75
Greater than or equal to .75 to 1 but less than .90 to 1 [Member] | LIBOR [Member]	'
Debt Instrument [Line Items]	'
Debt instrument interest rate terms, in percentage	2.25%
Greater than or equal to .75 to 1 but less than .90 to 1 [Member] | ABR [Member]	'
Debt Instrument [Line Items]	'
Debt instrument interest rate terms, in percentage	0.75%
Greater than .90 to 1 but less than or equal 1 [Member] | Minimum [Member]	'
Debt Instrument [Line Items]	'
Ratio of Total Outstanding Borrowings to Borrowing Base	0.9
Greater than .90 to 1 but less than or equal 1 [Member] | LIBOR [Member]	'
Debt Instrument [Line Items]	'
Debt instrument interest rate terms, in percentage	2.50%
Greater than .90 to 1 but less than or equal 1 [Member] | ABR [Member]	'
Debt Instrument [Line Items]	'
Debt instrument interest rate terms, in percentage	1.00%

Asset_Retirement_Obligations_S

Asset Retirement Obligations - Schedule of Changes in Asset Retirement Obligations (Detail) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'
Balance at December 31, 2012	$23,234
Liabilities incurred during period	3,066
Liabilities settled during period	23
Accretion expense during period	895	[1]
Revisions to estimates	213
Balance at September 30, 2013	$27,431
[1]	Included in depreciation, depletion and amortization on the Company’s Condensed Consolidated Statement of Operations.

Asset_Retirement_Obligations_A

Asset Retirement Obligations - Additional Information (Detail) (USD $)	Sep. 30, 2013
In Millions, unless otherwise specified
Asset Retirement Obligation Disclosure [Abstract]	'
Total asset retirement obligations, current portion	$0.40

StockBased_Compensation_Additi

Stock-Based Compensation - Additional Information (Detail) (USD $)

9 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

9 Months Ended

In Thousands, unless otherwise specified

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Feb. 15, 2013

Sep. 30, 2013

Jul. 30, 2012

Restricted Stock [Member]

Restricted Stock [Member]

Restricted Stock [Member]

Restricted Stock [Member]

Restricted Stock [Member]

Restricted Stock [Member]

Performance Share Units [Member]

Performance Share Units [Member]

Performance Share Units [Member]

Performance Share Units [Member]

Performance Share Units [Member]

Performance Share Units [Member]

PSU 2013 Grants [Member]

PSU 2013 Grants [Member]

PSU 2012 Grants [Member]

PSU 2012 Grants [Member]

Minimum [Member]

Maximum [Member]

Minimum [Member]

Maximum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Award vesting period

'

'

'

'

'3 years

'

'

'

'

'

'

'

'

'

'

'

'

'

Annual forfeiture rate

'

'

'

'

'

'

0.00%

11.00%

'

'

2.70%

'

'

'

'

'

'

'

Stock-based compensation expense

$8,411

$6,627

$2,600

$2,600

$7,100

$6,500

'

'

$500

$200

$1,300

$200

'

'

'

'

'

'

Right to received shares of common stock

'

'

'

'

'

'

'

'

1

'

1

'

'

'

'

'

'

'

Performance share units initial performance period, years

'

'

'

'

'

'

'

'

'

'

'3 years

'

'

'

'

'

'

'

PSU granted percentage of earnings

'

'

'

'

'

'

'

'

'

'

'

'

0.00%

200.00%

'

'

'

'

Amortized performance period

'

'

'

'

'

'

'

'

'

'

'4 years

'

'

'

'4 years

'

'4 years 2 days

'

Number of trading days

'

'

'

'

'

'

'

'

'

'

'30 days

'

'

'

'

'

'

'

Valuation model standard deviation term

'

'

'

'

'

'

'

'

'

'

'2 years

'

'

'

'

'

'

'

Expected percentage earned

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

112.00%

'

98.00%

StockBased_Compensation_Summar

Stock-Based Compensation - Summary of Performance Share Units (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013
Weighted Average Grant Date Fair Value per Unit (in dollars per share)	'
Vested, Weighted Average Grant Date Fair Value per Unit	$0
Performance Share Units [Member]	'
PSUs (in shares)	'
Non-vested shares outstanding, Beginning Balance	155,220
Granted	135,620
Vested	'
Forfeited	-21,540
Non-vested shares outstanding, Ending Balance	269,300
Weighted Average Grant Date Fair Value per Unit (in dollars per share)	'
Non-vested PSUs outstanding, Beginning Balance, Weighted Average Grant Date Fair Value per Unit	$26.22
Granted, Weighted Average Grant Date Fair Value per Unit	$42.01
Forfeited, Weighted Average Grant Date Fair Value per Unit	$32.89
Non-vested PSUs outstanding, Ending Balance, Weighted Average Grant Date Fair Value per Unit	$33.64

StockBased_Compensation_Summar1

Stock-Based Compensation - Summary of Assumptions (Detail)	9 Months Ended
	Sep. 30, 2013
2013 Grants [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Forecast period (years)	'4 years
Risk-free rate	0.65%
Oasis volatility	47.48%
2012 Grants [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Forecast period (years)	'4 years 2 days
Risk-free rate	0.46%
Oasis volatility	51.00%

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Tax Disclosure [Abstract]	'	'	'	'
Effective tax rate	38.20%	38.50%	37.20%	37.60%

Earnings_Per_Share_Schedule_of

Earnings Per Share - Schedule of Weighted-Average Number of Shares Outstanding (Detail)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]	'	'	'	'
Basic weighted average common shares outstanding	92,449	92,186	92,408	92,164
Dilution effect of stock awards at end of period	387	230	430	179
Diluted weighted average common shares outstanding	92,836	92,416	92,838	92,343
Anti-dilutive stock-based compensation awards	789	748	719	541

Business_Segment_Information_A

Business Segment Information - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2013
	Segment
Segment Reporting [Abstract]	'
Current operating units	3

Business_Segment_Information_S

Business Segment Information - Summarized Financial Information of Segments (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	$305,498	$184,711	$808,384	$472,341	'
Operating income	150,862	72,038	382,265	190,373	'
Other income (expense)	-62,648	-42,273	-106,170	-12,863	'
Income before income taxes	88,214	29,765	276,095	177,510	'
Total assets	4,083,383	'	4,083,383	'	2,528,794
Exploration and Production [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	286,952	178,748	770,445	461,857	'
Well Services [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	17,090	5,963	34,266	10,484	'
Midstream Services [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	1,456	'	3,673	'	'
Operating Segments [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	351,665	215,908	914,162	516,766	'
Operating income	150,862	72,038	382,265	190,373	'
Other income (expense)	-62,648	-42,273	-106,170	-12,863	'
Income before income taxes	88,214	29,765	276,095	177,510	'
Total assets	4,083,383	'	4,083,383	'	2,528,794
Operating Segments [Member] | Exploration and Production [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	286,952	178,748	770,445	461,857	'
Operating income	140,765	89,279	359,121	190,257	'
Other income (expense)	-62,628	-42,273	-106,159	-12,863	'
Income before income taxes	78,137	47,006	252,962	177,394	'
Total assets	3,916,554	'	3,916,554	'	2,475,820
Operating Segments [Member] | Well Services [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	57,116	37,160	124,266	54,909	'
Operating income	5,870	-17,241	11,744	116	'
Other income (expense)	-20	'	-11	'	'
Income before income taxes	5,850	-17,241	11,733	116	'
Total assets	68,869	'	68,869	'	52,974
Operating Segments [Member] | Midstream Services [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	7,597	'	19,451	'	'
Operating income	4,227	'	11,400	'	'
Income before income taxes	4,227	'	11,400	'	'
Total assets	97,960	'	97,960	'	'
Intersegment Eliminations [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	-46,167	-31,197	-105,778	-44,425	'
Intersegment Eliminations [Member] | Well Services [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	-40,026	-31,197	-90,000	-44,425	'
Intersegment Eliminations [Member] | Midstream Services [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	($6,141)	'	($15,778)	'	'

Commitments_and_Contingencies_

Commitments and Contingencies - Additional Information (Detail) (USD $)	Sep. 30, 2013	Sep. 26, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013
In Millions, unless otherwise specified			Long Term Commitments [Member]	Long Term Commitments [Member]	Long Term Commitments [Member]	Long Term Commitments [Member]	Drilling contracts [Member]
				Williston Basin project [Member]	Williston Basin project [Member]	Williston Basin project [Member]
					Crude oil [Member]	Natural Gas [Member]
					MMBbls	MMcf
Commitments And Contingencies [Line Items]	'	'	'	'	'	'	'
Total rental commitments under leases	$11.50	'	'	'	'	'	'
Payments upon early contract termination	'	'	'	'	'	'	24.9
Minimum quantity of delivery	'	'	'	'	14.3	12,800	'
Maximum commitment term	'	'	'	'6 years	'	'	'
Future obligations under supply agreements	'	'	55.5	'	'	'	'
Investment commitment	$7.20	$8.20	'	'	'	'	'

Condensed_Consolidating_Financ2

Condensed Consolidating Financial Information - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2013
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
Ownership percentage, Guarantors	100.00%

Condensed_Consolidating_Financ3

Condensed Consolidating Financial Information - Schedule of Condensed Consolidating Balance Sheet (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
ASSETS	'	'	'	'
Cash and cash equivalents	$125,440	$213,447	$280,303	$470,872
Restricted cash	986,210	0	'	'
Short-term investments	0	25,891	'	'
Accounts receivable — oil and gas revenues	155,068	110,341	'	'
Accounts receivable — joint interest partners	120,058	99,194	'	'
Accounts receivable – from affiliates	'	'	'	'
Inventory	18,358	20,707	'	'
Prepaid expenses	7,440	1,770	'	'
Advances to joint interest partners	1,170	1,985	'	'
Derivative instruments	374	19,016	'	'
Deferred income taxes	8,683	'	'	'
Other current assets	473	335	'	'
Total current assets	1,423,274	492,686	'	'
Property, plant and equipment	'	'	'	'
Oil and gas properties (successful efforts method)	3,044,515	2,348,128	'	'
Other property and equipment	157,926	49,732	'	'
Less: accumulated depreciation, depletion, amortization and impairment	-589,173	-391,260	'	'
Total property, plant and equipment, net	2,613,268	2,006,600	'	'
Derivative instruments	3,405	4,981	'	'
Deferred income taxes	'	'	'	'
Deferred costs and other assets	43,436	24,527	'	'
Total assets	4,083,383	2,528,794	'	'
LIABILITIES AND STOCKHOLDERS’ EQUITY	'	'	'	'
Accounts payable	39,468	12,491	'	'
Accounts payable – from affiliates	'	'	'	'
Advances from joint interest partners	13,211	21,176	'	'
Revenues and production taxes payable	133,083	71,553	'	'
Accrued liabilities	198,493	189,863	'	'
Accrued interest payable	22,873	30,096	'	'
Derivative instruments	17,060	1,048	'	'
Deferred income taxes	0	4,558	'	'
Total current liabilities	424,188	330,785	'	'
Long-term debt	2,360,000	1,200,000	'	'
Asset retirement obligations	26,999	22,956	'	'
Derivative instruments	852	380	'	'
Deferred income taxes	293,156	177,671	'	'
Other liabilities	2,310	1,997	'	'
Total liabilities	3,107,505	1,733,789	'	'
Stockholders’ equity	'	'	'	'
Common stock, $0.01 par value; 300,000,000 shares authorized; 93,854,867 issued and 93,690,494 outstanding at September 30, 2013; 93,432,712 issued and 93,303,298 outstanding at December 31, 2012	926	925	'	'
Treasury stock, at cost; 164,373 and 129,414 shares at September 30, 2013 and December 31, 2012, respectively	-5,220	-3,796	'	'
Additional paid-in-capital	666,770	657,943	'	'
Retained earnings	313,402	139,933	'	'
Total stockholders’ equity	975,878	795,005	'	'
Total liabilities and stockholders’ equity	4,083,383	2,528,794	'	'
Parent/Issuer [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	32,955	133,797	231,170	443,482
Restricted cash	986,210	'	'	'
Short-term investments	'	25,891	'	'
Accounts receivable – from affiliates	770	310	'	'
Prepaid expenses	477	313	'	'
Other current assets	2	235	'	'
Total current assets	1,020,414	160,546	'	'
Property, plant and equipment	'	'	'	'
Investments in and advances to subsidiaries	2,082,828	1,807,010	'	'
Deferred income taxes	69,795	42,746	'	'
Deferred costs and other assets	34,128	20,748	'	'
Total assets	3,207,165	2,031,050	'	'
LIABILITIES AND STOCKHOLDERS’ EQUITY	'	'	'	'
Accounts payable	'	9	'	'
Accounts payable – from affiliates	8,432	5,845	'	'
Accrued liabilities	46	100	'	'
Accrued interest payable	22,809	30,091	'	'
Total current liabilities	31,287	36,045	'	'
Long-term debt	2,200,000	1,200,000	'	'
Total liabilities	2,231,287	1,236,045	'	'
Stockholders’ equity	'	'	'	'
Common stock, $0.01 par value; 300,000,000 shares authorized; 93,854,867 issued and 93,690,494 outstanding at September 30, 2013; 93,432,712 issued and 93,303,298 outstanding at December 31, 2012	926	925	'	'
Treasury stock, at cost; 164,373 and 129,414 shares at September 30, 2013 and December 31, 2012, respectively	-5,220	-3,796	'	'
Additional paid-in-capital	666,770	657,943	'	'
Retained earnings	313,402	139,933	'	'
Total stockholders’ equity	975,878	795,005	'	'
Total liabilities and stockholders’ equity	3,207,165	2,031,050	'	'
Combined Guarantor Subsidiaries [Member]	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	92,485	79,650	49,133	27,390
Accounts receivable — oil and gas revenues	155,068	110,341	'	'
Accounts receivable — joint interest partners	120,058	99,194	'	'
Accounts receivable – from affiliates	8,432	5,845	'	'
Inventory	18,358	20,707	'	'
Prepaid expenses	6,963	1,457	'	'
Advances to joint interest partners	1,170	1,985	'	'
Derivative instruments	374	19,016	'	'
Deferred income taxes	8,683	'	'	'
Other current assets	471	100	'	'
Total current assets	412,062	338,295	'	'
Property, plant and equipment	'	'	'	'
Oil and gas properties (successful efforts method)	3,044,515	2,348,128	'	'
Other property and equipment	157,926	49,732	'	'
Less: accumulated depreciation, depletion, amortization and impairment	-589,173	-391,260	'	'
Total property, plant and equipment, net	2,613,268	2,006,600	'	'
Derivative instruments	3,405	4,981	'	'
Deferred costs and other assets	9,308	3,779	'	'
Total assets	3,038,043	2,353,655	'	'
LIABILITIES AND STOCKHOLDERS’ EQUITY	'	'	'	'
Accounts payable	39,468	12,482	'	'
Accounts payable – from affiliates	770	310	'	'
Advances from joint interest partners	13,211	21,176	'	'
Revenues and production taxes payable	133,083	71,553	'	'
Accrued liabilities	198,447	189,763	'	'
Accrued interest payable	64	5	'	'
Derivative instruments	17,060	1,048	'	'
Deferred income taxes	'	4,558	'	'
Total current liabilities	402,103	300,895	'	'
Long-term debt	160,000	'	'	'
Asset retirement obligations	26,999	22,956	'	'
Derivative instruments	852	380	'	'
Deferred income taxes	362,951	220,417	'	'
Other liabilities	2,310	1,997	'	'
Total liabilities	955,215	546,645	'	'
Stockholders’ equity	'	'	'	'
Capital contributions from affiliates	1,643,729	1,586,780	'	'
Additional paid-in-capital	8,743	8,743	'	'
Retained earnings	430,356	211,487	'	'
Total stockholders’ equity	2,082,828	1,807,010	'	'
Total liabilities and stockholders’ equity	3,038,043	2,353,655	'	'
Intercompany Eliminations [Member]	'	'	'	'
ASSETS	'	'	'	'
Accounts receivable – from affiliates	-9,202	-6,155	'	'
Total current assets	-9,202	-6,155	'	'
Property, plant and equipment	'	'	'	'
Investments in and advances to subsidiaries	-2,082,828	-1,807,010	'	'
Deferred income taxes	-69,795	-42,746	'	'
Total assets	-2,161,825	-1,855,911	'	'
LIABILITIES AND STOCKHOLDERS’ EQUITY	'	'	'	'
Accounts payable – from affiliates	-9,202	-6,155	'	'
Total current liabilities	-9,202	-6,155	'	'
Deferred income taxes	-69,795	-42,746	'	'
Total liabilities	-78,997	-48,901	'	'
Stockholders’ equity	'	'	'	'
Capital contributions from affiliates	-1,643,729	-1,586,780	'	'
Additional paid-in-capital	-8,743	-8,743	'	'
Retained earnings	-430,356	-211,487	'	'
Total stockholders’ equity	-2,082,828	-1,807,010	'	'
Total liabilities and stockholders’ equity	($2,161,825)	($1,855,911)	'	'

Condensed_Consolidating_Financ4

Condensed Consolidating Financial Information - Schedule of Condensed Consolidating Balance Sheet (Parenthetical) (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]	'	'
Common stock, par value (in dollars per share)	$0.01	$0.01
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	93,854,867	93,432,712
Common stock, shares outstanding	93,690,494	93,303,298
Treasury stock, shares	164,373	129,414

Condensed_Consolidating_Financ5

Condensed Consolidating Financial Information - Schedule of Condensed Consolidating Statement of Operations (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues	'	'	'	'
Oil and gas revenues	$286,952	$178,748	$770,445	$461,857
Well services and midstream revenues	18,546	5,963	37,939	10,484
Total revenues	305,498	184,711	808,384	472,341
Expenses	'	'	'	'
Lease operating expenses	21,831	16,134	59,586	37,979
Well services and midstream operating expenses	10,319	5,420	19,877	7,104
Marketing, transportation and gathering expenses	5,688	2,744	19,856	7,283
Production taxes	26,823	16,433	70,309	43,419
Depreciation, depletion and amortization	72,728	57,684	205,779	140,783
Exploration expenses	463	336	2,712	3,171
Impairment of oil and gas properties	56	36	762	2,607
General and administrative expenses	16,728	13,886	47,238	39,622
Total expenses	154,636	112,673	426,119	281,968
Operating income (loss)	150,862	72,038	382,265	190,373
Other income (expense)	'	'	'	'
Equity in earnings in subsidiaries	'	'	'	'
Net gain (loss) on derivative instruments	-39,817	-22,441	-41,838	33,568
Interest expense, net of capitalized interest	-22,854	-20,979	-65,429	-48,952
Other income	23	1,147	1,097	2,521
Total other income (expense)	-62,648	-42,273	-106,170	-12,863
Income before income taxes	88,214	29,765	276,095	177,510
Income tax benefit (expense)	-33,715	-11,451	-102,626	-66,712
Net income	54,499	18,314	173,469	110,798
Parent/Issuer [Member]	'	'	'	'
Expenses	'	'	'	'
General and administrative expenses	3,746	2,988	10,146	8,078
Total expenses	3,746	2,988	10,146	8,078
Operating income (loss)	-3,746	-2,988	-10,146	-8,078
Other income (expense)	'	'	'	'
Equity in earnings in subsidiaries	70,118	32,735	218,869	145,021
Interest expense, net of capitalized interest	-21,277	-20,307	-61,955	-47,136
Other income	15	238	-348	533
Total other income (expense)	48,856	12,666	156,566	98,418
Income before income taxes	45,110	9,678	146,420	90,340
Income tax benefit (expense)	9,389	8,636	27,049	20,458
Net income	54,499	18,314	173,469	110,798
Combined Guarantor Subsidiaries [Member]	'	'	'	'
Revenues	'	'	'	'
Oil and gas revenues	286,952	178,748	770,445	461,857
Well services and midstream revenues	18,546	5,963	37,939	10,484
Total revenues	305,498	184,711	808,384	472,341
Expenses	'	'	'	'
Lease operating expenses	21,831	16,134	59,586	37,979
Well services and midstream operating expenses	10,319	5,420	19,877	7,104
Marketing, transportation and gathering expenses	5,688	2,744	19,856	7,283
Production taxes	26,823	16,433	70,309	43,419
Depreciation, depletion and amortization	72,728	57,684	205,779	140,783
Exploration expenses	463	336	2,712	3,171
Impairment of oil and gas properties	56	36	762	2,607
General and administrative expenses	12,982	10,898	37,092	31,544
Total expenses	150,890	109,685	415,973	273,890
Operating income (loss)	154,608	75,026	392,411	198,451
Other income (expense)	'	'	'	'
Equity in earnings in subsidiaries	'	'	'	'
Net gain (loss) on derivative instruments	-39,817	-22,441	-41,838	33,568
Interest expense, net of capitalized interest	-1,577	-672	-3,474	-1,816
Other income	8	909	1,445	1,988
Total other income (expense)	-41,386	-22,204	-43,867	33,740
Income before income taxes	113,222	52,822	348,544	232,191
Income tax benefit (expense)	-43,104	-20,087	-129,675	-87,170
Net income	70,118	32,735	218,869	145,021
Intercompany Eliminations [Member]	'	'	'	'
Other income (expense)	'	'	'	'
Equity in earnings in subsidiaries	-70,118	-32,735	-218,869	-145,021
Total other income (expense)	-70,118	-32,735	-218,869	-145,021
Income before income taxes	-70,118	-32,735	-218,869	-145,021
Net income	($70,118)	($32,735)	($218,869)	($145,021)

Condensed_Consolidating_Financ6

Condensed Consolidating Financial Information - Schedule of Condensed Consolidating Statement of Cash Flows (Detail) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:	'	'
Net income	$173,469	$110,798
Adjustments to reconcile net income to net cash provided by (used in) operating activities:	'	'
Depreciation, depletion and amortization	205,779	140,783
Impairment of oil and gas properties	762	2,607
Deferred income taxes	102,244	66,648
Derivative instruments	41,838	-33,568
Stock-based compensation expenses	8,411	6,627
Debt discount amortization and other	2,693	2,038
Working capital and other changes:	'	'
Change in accounts receivable	-67,487	-69,163
Change in inventory	-8,820	-26,790
Change in prepaid expenses	-5,175	-2,009
Change in other current assets	-138	413
Change in other assets	-63	-119
Change in accounts payable and accrued liabilities	82,246	79,079
Change in other current liabilities	0	4,784
Change in other liabilities	922	0
Net cash provided by operating activities	536,681	282,128
Cash flows from investing activities:	'	'
Capital expenditures	-654,175	-777,516
Acquisition of oil and gas properties	-133,061	0
Increase in restricted cash	-986,210	0
Derivative settlements	-5,135	2,784
Purchases of short-term investments	0	-126,213
Redemptions of short-term investments	25,000	19,994
Advances from joint interest partners	-7,965	17,508
Net cash used in investing activities	-1,761,546	-863,443
Cash flows from financing activities:	'	'
Proceeds from credit facility	160,000	0
Proceeds from issuance of senior notes	1,000,000	400,000
Purchases of treasury stock	-1,424	-1,299
Debt issuance costs	-21,718	-7,955
Investment in / capital contributions from affiliates	0	'
Net cash provided by financing activities	1,136,858	390,746
Decrease in cash and cash equivalents	-88,007	-190,569
Beginning of period	213,447	470,872
End of period	125,440	280,303
Parent/Issuer [Member]	'	'
Cash flows from operating activities:	'	'
Net income	173,469	110,798
Adjustments to reconcile net income to net cash provided by (used in) operating activities:	'	'
Equity in earnings of subsidiaries	-218,869	-145,021
Deferred income taxes	-27,049	-20,458
Stock-based compensation expenses	8,196	6,397
Debt discount amortization and other	2,850	1,616
Working capital and other changes:	'	'
Change in accounts receivable	-460	-203
Change in prepaid expenses	-164	-192
Change in other current assets	233	-60
Change in other assets	'	-24
Change in accounts payable and accrued liabilities	-4,758	8,620
Net cash provided by operating activities	-66,552	-38,527
Cash flows from investing activities:	'	'
Increase in restricted cash	-986,210	'
Purchases of short-term investments	'	-126,213
Redemptions of short-term investments	25,000	19,994
Net cash used in investing activities	-961,210	-106,219
Cash flows from financing activities:	'	'
Proceeds from issuance of senior notes	1,000,000	400,000
Purchases of treasury stock	-1,424	-1,299
Debt issuance costs	-15,340	-7,255
Investment in / capital contributions from affiliates	-56,316	-459,012
Net cash provided by financing activities	926,920	-67,566
Decrease in cash and cash equivalents	-100,842	-212,312
Beginning of period	133,797	443,482
End of period	32,955	231,170
Combined Guarantor Subsidiaries [Member]	'	'
Cash flows from operating activities:	'	'
Net income	218,869	145,021
Adjustments to reconcile net income to net cash provided by (used in) operating activities:	'	'
Depreciation, depletion and amortization	205,779	140,783
Impairment of oil and gas properties	762	2,607
Deferred income taxes	129,293	87,106
Derivative instruments	41,838	-33,568
Stock-based compensation expenses	215	230
Debt discount amortization and other	-157	422
Working capital and other changes:	'	'
Change in accounts receivable	-69,614	-70,899
Change in inventory	-8,820	-26,790
Change in prepaid expenses	-5,011	-1,817
Change in other current assets	-371	473
Change in other assets	-63	-95
Change in accounts payable and accrued liabilities	89,591	72,398
Change in other current liabilities	'	4,784
Change in other liabilities	922	'
Net cash provided by operating activities	603,233	320,655
Cash flows from investing activities:	'	'
Capital expenditures	-654,175	-777,516
Acquisition of oil and gas properties	-133,061	'
Derivative settlements	-5,135	2,784
Advances from joint interest partners	-7,965	17,508
Net cash used in investing activities	-800,336	-757,224
Cash flows from financing activities:	'	'
Proceeds from credit facility	160,000	'
Debt issuance costs	-6,378	-700
Investment in / capital contributions from affiliates	56,316	459,012
Net cash provided by financing activities	209,938	458,312
Decrease in cash and cash equivalents	12,835	21,743
Beginning of period	79,650	27,390
End of period	92,485	49,133
Intercompany Eliminations [Member]	'	'
Cash flows from operating activities:	'	'
Net income	-218,869	-145,021
Adjustments to reconcile net income to net cash provided by (used in) operating activities:	'	'
Equity in earnings of subsidiaries	218,869	145,021
Working capital and other changes:	'	'
Change in accounts receivable	2,587	1,939
Change in accounts payable and accrued liabilities	($2,587)	($1,939)

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (USD $)	9 Months Ended						1 Months Ended		1 Months Ended	0 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2013	Apr. 05, 2013	Mar. 31, 2013	Sep. 30, 2013	Oct. 10, 2013	Oct. 31, 2013	Oct. 02, 2013	Oct. 02, 2013
			Drilling contracts [Member]	Second Amended Credit Facility [Member]	Second Amended Credit Facility [Member]	Second Amended Credit Facility [Member]	West Williston Acquisition [Member]	Subsequent Event [Member]	Subsequent Event [Member]	Subsequent Event [Member]	Subsequent Event [Member]
									Drilling contracts [Member]	Second Amended Credit Facility [Member]	West Williston Acquisition [Member]
											acre
Subsequent Event [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Acres acquired	'	'	'	'	'	'	'	'	'	'	136,000
Acquisition, consideration transferred	'	'	'	'	'	'	'	'	'	'	$1,478,600,000
Acquisition, consideration transferred, deposit	'	'	'	'	'	'	72,500,000	'	'	'	'
Proceeds from credit facility	160,000,000	0	'	'	'	'	'	'	'	440,000,000	'
Line of credit facility, amount outstanding	'	'	'	160,000,000	'	'	'	'	'	605,200,000	'
Line of credit facility, remaining borrowing capacity	'	'	'	1,334,800,000	'	'	'	'	'	894,800,000	'
Line of credit facility, maximum borrowing capacity	'	'	'	'	1,250,000,000	750,000,000	'	'	'	1,500,000,000	'
Payments upon early contract termination	'	'	24,900,000	'	'	'	'	'	9,700,000	'	'
Purchase Commitment, Remaining Minimum Amount Committed	'	'	'	'	'	'	'	$3,600,000	'	'	'