SM Energy (SM) 10-Q 29 Oct 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information Document	9 Months Ended
	Sep. 30, 2014	Oct. 22, 2014
Entity Information [Line Items]	'	'
Entity Registrant Name	'SM Energy Co	'
Entity Central Index Key	'0000893538	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Document Type	'10-Q	'
Document Period End Date	30-Sep-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q3	'
Amendment Flag	'false	'
Entity Common Stock, Shares Outstanding	'	67,405,401
Entity Current Reporting Status	'Yes	'

CONDENSED_CONSOLIDATED_BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (in thousands, except share amounts) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets	'	'
Cash and cash equivalents	$269	$282,248
Accounts receivable	304,175	318,371
Derivative asset	41,295	21,559
Deferred income taxes	9,084	10,749
Prepaid expense and other	16,782	14,574
Total current assets	371,605	647,501
Proved oil and gas properties	6,789,927	5,637,462
Less - accumulated depletion, depreciation, and amortization	-3,045,006	-2,583,698
Unproved oil and gas properties	536,100	271,100
Wells in progress	637,584	279,654
Oil and gas properties held for sale net of accumulated depletion, depreciation and amortization of $22,482 and $7,390, respectively	19,883	19,072
Other property and equipment, net of accumulated depreciation of $35,627 and $28,775, respectively	276,953	236,202
Total property and equipment, net	5,215,441	3,859,792
Derivative asset	22,510	30,951
Restricted cash	0	96,713
Other noncurrent assets	51,190	70,208
Total other noncurrent assets	73,700	197,872
Total Assets	5,660,746	4,705,165
Liabilities	'	'
Accounts payable and accrued expenses	664,925	606,751
Derivative liability	4,649	26,380
Other current liabilities	0	6,000
Total current liabilities	669,574	639,131
Revolving credit facility	390,000	0
Senior Notes (note 5)	1,600,000	1,600,000
Asset retirement obligation	123,905	115,659
Asset retirement obligation associated with oil and gas properties held for sale	452	3,033
Net Profits Plan liability	41,705	56,985
Deferred income taxes	846,698	650,125
Derivative liability	8,243	4,640
Other noncurrent liabilities	28,329	28,771
Total noncurrent liabilities	3,039,332	2,459,213
Commitments and contingencies (note 6)	'	'
Stockholders' equity:	'	'
Common stock, $0.01 par value - authorized: 200,000,000 shares; issued: 67,393,867 and 67,078,853 shares outstanding, respectively; net of treasury shares: 67,393,867 and 67,056,441, respectively	674	671
Additional paid-in-capital	273,783	257,720
Treasury stock, at cost: zero and 22,412 shares, respectively	0	-823
Retained earnings	1,682,273	1,354,669
Accumulated other comprehensive loss	-4,890	-5,416
Total stockholders' equity	1,951,840	1,606,821
Total Liabilities and Stockholders' Equity	$5,660,746	$4,705,165

Balance_Sheet_Parenthetical_Pa

Balance Sheet Parenthetical (Parentheticals) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization	$3,045,006,000	$2,583,698,000
Common Stock, Par or Stated Value Per Share	$0.01	$0.01
Common Stock, Shares Authorized	200,000,000	200,000,000
Common Stock, Shares, Issued	67,393,867	67,078,853
Common Stock, Shares, Outstanding	67,393,867	67,056,441
Treasury Stock, Shares	0	22,412
Assets Held-for-sale [Member]	'	'
Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization	22,482,000	7,390,000
Other Capitalized Property Plant and Equipment [Member]	'	'
Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization	$35,627,000	$28,775,000

CONDENSED_CONSOLIDATED_STATEME

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) (in thousands, except per share amounts) (USD $)	3 Months Ended				9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Operating revenues:	'		'		'		'
Oil, gas, and NGL production revenue	$617,207		$601,787		$1,894,977		$1,605,882
Other operating revenues	1,579		11,320		31,509		50,765
Total operating revenues	618,786		613,107		1,926,486		1,656,647
Operating expenses:	'		'		'		'
Oil, gas, and NGL production expense	178,390		158,921		519,697		434,291
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	183,259		195,792		548,255		620,232
Exploration	34,556		16,280		80,161		52,335
Impairment of proved properties	0		5,935		0		61,706
Abandonment and impairment of unproved properties	15,522		3,818		18,487		8,459
General and administrative	41,696		33,920		114,862		101,574
Change in Net Profits Plan liability	-6,399		940		-15,280		-6,423
Derivative (gain) loss	-190,661	[1]	39,933	[1]	33,470	[1]	-14,685	[1]
Other operating expenses	5,444		20,084		19,505		71,192
Total operating expenses	261,807		475,623		1,319,157		1,328,681
Income from operations	356,979		137,484		607,329		327,966
Non-operating income (expense):	'		'		'		'
Interest expense	-22,621		-24,488		-70,851		-65,170
Other, net	-672		28		-2,493		64
Income before income taxes	333,686		113,024		533,985		262,860
Income tax expense	-124,748		-42,334		-199,660		-98,921
Net income	$208,938		$70,690		$334,325		$163,939
Basic weighted-average common shares outstanding	67,379		66,943		67,169		66,486
Diluted weighted-average common shares outstanding	68,430		68,253		68,258		67,969
Basic net income per common share	$3.10		$1.06		$4.98		$2.47
Diluted net income per common share	$3.05		$1.04		$4.90		$2.41
Dividends per common share	$0.05		$0.05		$0.10		$0.10
[1]	(2)B Total derivative (gain) loss is reported in the derivative (gain) loss line item on the condensed consolidated statements of cash flows within net cash provided by operating activities.

CONDENSED_CONSOLIDATED_STATEME1

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (USD $)	3 Months Ended				9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Statement of Comprehensive Income [Abstract]	'		'		'		'
Net income	$208,938		$70,690		$334,325		$163,939
Reclassification to earnings	0	[1]	308	[1]	0	[1]	1,115	[1]
Pension liability adjustment	196		0		526		-3
Total other comprehensive income, net of tax	196		308		526		1,112
Total comprehensive income	$209,134		$70,998		$334,851		$165,051
[1]	Reclassification from accumulated other comprehensive loss (bAOCLb) related to de-designated hedges. As of December 31, 2013, all commodity derivative contracts that had been designated as cash flow hedges were settled and reclassified into earnings from AOCL.

CONDENSED_CONSOLIDATED_STATEME2

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013
Statement of Cash Flows [Abstract]	'		'
Net income	$334,325		$163,939
Adjustments to reconcile net income to net cash provided by operating activities:	'		'
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	548,255		620,232
Exploratory dry hole expense	22,844		5,878
Impairment of proved properties	0		61,706
Abandonment and impairment of unproved properties	18,487		8,459
Stock-based compensation expense	24,568		25,495
Change in Net Profits Plan liability	-15,280		-6,423
Derivative (gain) loss	33,470	[1]	-14,685	[1]
Derivative cash settlement (gain) loss	-62,894	[2]	12,715	[2]
Amortization of deferred financing costs	4,433		3,914
Deferred income taxes	198,180		98,619
Plugging and abandonment	-6,193		-7,453
Other, net	-2,986		3,439
Changes in current assets and liabilities:	'		'
Accounts receivable	6,476		-45,209
Prepaid expenses and other	234		-2,461
Accounts payable and accrued expenses	-28,797		72,704
Net Cash Provided by Operating Activities	1,075,122		1,000,869
Cash flows from investing activities:	'		'
Net proceeds from sale of oil and gas properties	41,868		20,498
Capital expenditures	-1,317,862		-1,121,355
Acquisition of proved and unproved oil and gas properties	-459,277		-62,007
Other, net	-714		-3,509
Net cash used in investing activities	-1,735,985		-1,166,373
Cash flows from financing activities:	'		'
Proceeds from credit facility	536,500		976,500
Repayment of credit facility	-146,500		-1,288,500
Deferred financing costs related to credit facility	0		-3,444
Net proceeds from 2024 Notes	0		490,274
Proceeds from sale of common stock	2,898		4,450
Dividends paid	-3,353		-3,314
Net share settlement from issuance of stock awards	-10,576		-16,203
Other, net	-85		-9
Net cash provided by financing activities	378,884		159,754
Net change in cash and cash equivalents	-281,979		-5,750
Cash and cash equivalents at beginning of period	282,248		5,926
Cash and cash equivalents at ending of period	269		176
Supplemental schedule of additional cash flow information and noncash investing and financing activities:	'		'
Cash paid for interest, net of capitalized interest	79,119		59,841
Net cash paid (refunded) for income taxes	$1,979		($259)
[1]	(2)B Total derivative (gain) loss is reported in the derivative (gain) loss line item on the condensed consolidated statements of cash flows within net cash provided by operating activities.
[2]	(1)B Total derivative cash settlement (gain) loss is reported in the derivative cash settlement gain (loss) line item on the condensed consolidated statements of cash flows within net cash provided by operating activities.

CONDENSED_CONSOLIDATED_STATEME3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) (in thousands) (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Cash Flows [Abstract]	'	'	'	'
Dividends, Common Stock	'	'	$3.40	$3.30
Capital Expenditures Incurred but Not yet Paid	'	'	404.8	238.7
Noncash or Part Noncash Acquisition, Net Nonmonetary Assets Acquired (Liabilities Assumed)	$6.20	$25	'	'

The_Company_and_Business

The Company and Business	9 Months Ended
	Sep. 30, 2014
Company and Business Disclosure [Abstract]	'
The Company and Business	'
	Note 1 - The Company and Business
	SM Energy Company (“SM Energy” or the “Company”) is an independent energy company engaged in the acquisition, exploration, development, and production of crude oil and condensate, natural gas, and natural gas liquids (also respectively referred to as “oil,” “gas,” and “NGLs” throughout this report) in onshore North America, with a current focus on oil and liquids-rich resource plays.

Basis_of_Presentation_Signific

Basis of Presentation, Significant Accounting Policies, and Recently Issued Accounting Standards	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Basis of Presentation, Significant Accounting Policies, and Recently Issued Accounting Standards	'
	Note 2 - Basis of Presentation, Significant Accounting Policies, and Recently Issued Accounting Standards
	Basis of Presentation
	The accompanying unaudited condensed consolidated financial statements of SM Energy have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial information and the instructions to Form 10-Q and Regulation S-X. They do not include all information and notes required by GAAP for complete financial statements. However, except as disclosed herein, there has been no material change in the information disclosed in the notes to consolidated financial statements included in SM Energy’s Annual Report on Form 10-K for the year ended December 31, 2013 (the “2013 Form 10-K”). In the opinion of management, all adjustments, consisting of normal recurring accruals considered necessary for a fair presentation of interim financial information, have been included. Operating results for the periods presented are not necessarily indicative of expected results for the full year. In connection with the preparation of its unaudited condensed consolidated financial statements, the Company evaluated events subsequent to the balance sheet date of September 30, 2014, through the filing date of this report.
	Significant Accounting Policies
	The significant accounting policies followed by the Company are set forth in Note 1 to the Company’s consolidated financial statements in its 2013 Form 10-K, and are supplemented by the notes to the unaudited condensed consolidated financial statements in this report. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in the 2013 Form 10-K.
	Recently Issued Accounting Standards
	In April 2014, the Financial Accounting Standards Board (“FASB”) issued new authoritative accounting guidance related to the recognition and presentation of discontinued operations in the financial statements.  This guidance intends to reduce the frequency of disposals reported as discontinued operations by focusing on strategic shifts that have, or will have, a major effect on an entity’s operations and financial results.  This guidance is to be applied prospectively and is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2014.  Early application is permitted. The Company is currently evaluating the provisions of this guidance and assessing its impact on the Company’s financial statements and disclosures.
	In May 2014, the FASB issued new authoritative accounting guidance related to the recognition of revenue from contracts with customers. This guidance is to be applied using a retrospective method or a modified retrospective method, as outlined in the guidance, and is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2016. Early application is not permitted. The Company is currently evaluating the provisions of this guidance and assessing its impact on the Company’s financial statements and disclosures.
	In June 2014, the FASB issued new authoritative accounting guidance related to the recognition of share-based compensation when an award provides that a performance target can be achieved after the requisite service period.  This guidance may be applied either prospectively or retrospectively and is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2015.  Early application is permitted. The Company is currently evaluating the provisions of this guidance and assessing its impact on the Company’s financial statements and disclosures.
	In August 2014, the FASB issued new authoritative guidance that requires management to evaluate whether there are conditions or events that raise substantial doubt about an entity’s ability to continue as a going concern within one year after the date that the entity’s financial statements are issued, or within one year after the date that the entity’s financial statements are available to be issued, and to provide disclosures when certain criteria are met.  This guidance is effective for the annual period ending after December 15, 2016, and for annual periods and interim periods thereafter. Early application is permitted.  The Company is currently evaluating the provisions of this guidance and assessing its impact on the Company’s financial statements and disclosures.
	There are no other new significant accounting standards applicable to the Company that have been issued but not yet adopted by the Company as of September 30, 2014, and through the filing date of this report.

Assets_Held_for_Sale_Assets_He

Assets Held for Sale Assets Held for Sale	9 Months Ended
	Sep. 30, 2014
Assets held for sale [Abstract]	'
Assets Held-for-sale	'
	Note 3 – Acquisitions, Divestitures, and Assets Held for Sale
	Gooseneck Prospect Acquisition
	On September 24, 2014, the Company acquired approximately 61,000 net acres of proved and unproved oil and gas properties in the Company’s Gooseneck prospect area in North Dakota, along with other related equipment, contracts, records and other assets (collectively the “Assets”). Total consideration paid by the Company was $325.2 million in cash and the effective date for the acquisition was July 1, 2014.
	It was determined that this acquisition met the definition of a business combination under ASC 805, Business Combinations, as it included proved properties. The Company allocated the preliminary adjusted purchase price to the acquired assets and liabilities based on fair values as of the acquisition date of September 24, 2014, as summarized in the following table. This acquisition is subject to normal post-closing adjustments, which are expected to be completed in early 2015. Refer to Note 11 - Fair Value Measurements for additional discussion on the valuation techniques used in determining the fair value of acquired properties.
	Purchase Price	As of September 24, 2014
		(in thousands)
	Cash consideration	$	325,230
	Fair value of assets acquired:
	Proved oil and gas properties	$	201,842
	Unproved oil and gas properties	125,562
	Total fair value of oil and gas properties acquired	327,404
	Working capital	(61		)
	Asset retirement obligation	(2,113		)
	Total fair value of net assets acquired	$	325,230
	Rocky Mountain Acquisitions
	In addition to the Gooseneck prospect acquisition discussed above, the Company acquired other proved and unproved properties in its Rocky Mountain region during the nine months ended September 30, 2014, from multiple sellers for approximately $134.1 million in total cash consideration plus approximately 7,000 net acres of non-core assets in the Company’s Rocky Mountain region. These acquisitions are subject to normal post-closing adjustments, which are expected to be completed in late 2014 and early 2015.
	Subsequent to September 30, 2014, the Company closed an acquisition of proved and unproved properties in its Gooseneck prospect area for total cash consideration of approximately $84.8 million. This acquisition is subject to normal post-closing adjustments, which are expected to be completed in early 2015.
	Divestitures
	During the second quarter of 2014, the Company divested certain non-strategic assets in the Williston Basin located in its Rocky Mountain region. Total cash proceeds received at closing (referred throughout this report as “divestiture proceeds”) were $50.2 million and the estimated net gain is $26.8 million. This divestiture is subject to normal post-closing adjustments, which are expected to be completed during the fourth quarter of 2014.
	Assets Held for Sale
	Assets are classified as held for sale when the Company commits to a plan to sell the assets and there is reasonable certainty the sale will take place within one year. Upon classification as held for sale, long-lived assets are no longer depreciated or depleted, and a measurement for impairment is performed to identify and expense any excess of carrying value over fair value less estimated costs to sell. Subsequent decreases to the estimated fair value less the costs to sell impact the measurement of assets held for sale.
	As of September 30, 2014, the accompanying condensed consolidated balance sheets (“accompanying balance sheets”) present $19.9 million of oil and gas properties held for sale, net of accumulated depletion, depreciation, and amortization expense. A corresponding asset retirement obligation liability of $0.5 million is separately presented. Assets held for sale are recorded at the lesser of their respective carrying value or fair value less estimated costs to sell. Certain assets classified as held for sale as of September 30, 2014, were written down to fair value less estimated costs to sell, which was recorded as a loss on divestiture activity and is included within the other operating revenues line item in the accompanying condensed consolidated statements of operations (“accompanying statements of operations”).
	The Company determined that these planned asset sales do not qualify for discontinued operations accounting under financial statement presentation authoritative guidance.

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2014
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Note 4 - Income Taxes
	Income tax expense for the three and nine months ended September 30, 2014, and 2013, differs from the amounts that would be provided by applying the statutory United States federal income tax rate to income before income taxes primarily due to the effect of state income taxes, changes in valuation allowances, percentage depletion, research and development (“R&D”) credits, and other permanent differences. The quarterly rate can also be impacted by the proportional effects of forecasted net income as of each period end presented.
	The provision for income taxes consists of the following:
		For the Three Months Ended September 30,						For the Nine Months Ended September 30,
		2014			2013			2014			2013
		(in thousands)
	Current portion of income tax (benefit) expense:
	Federal	$	—		$	—		$	—		$	—
	State	479			(46		)	1,480			302
	Deferred portion of income tax expense	124,269			42,380			198,180			98,619
	Total income tax expense	$	124,748		$	42,334		$	199,660		$	98,921
		37.4		%	37.5		%	37.4		%	37.6		%
	A change in the Company’s effective tax rate between reported periods will generally reflect differences in its estimated highest marginal state tax rate due to changes in the composition of income from Company activities among various state tax jurisdictions. Cumulative effects of state rate changes are reflected in the period legislation is enacted.
	The Company and its subsidiaries file federal income tax returns and various state income tax returns. With certain exceptions, the Company is no longer subject to United States federal or state income tax examinations by tax authorities for years before 2007. Federal tax law allowing for the calculation of an R&D credit was enacted in 2013, which allowed the credit for the 2012 and 2013 tax years. However, the Company has not yet commissioned a study to calculate the credit for these tax years. The table above excludes the impact for any credit that could be claimed for the 2013 tax year. The Internal Revenue Service (“IRS”) initiated an audit in the first quarter of 2012 related to R&D tax credits claimed by the Company for the 2007 through 2010 tax years. On April 23, 2013, the IRS issued a Notice of Proposed Adjustment disallowing $4.6 million of R&D tax credits claimed for open tax years during the audit period. During the quarter ended September 30, 2014, the Company successfully reached an agreement with the IRS Appeals Office, which allowed the Company to claim a portion of these R&D credits and resulted in no significant adjustment.
	On September 13, 2013, the United States Department of the Treasury issued the final and re-proposed tangible property regulations effective for tax years beginning January 1, 2014. The Company has determined it is materially compliant with the requirements of these regulations.

LongTerm_Debt

Long-Term Debt	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Long-term debt	'
	Note 5 - Long-term Debt
	Revolving Credit Facility
	The Company’s Fifth Amended and Restated Credit Agreement provides a maximum loan amount of $2.5 billion, current aggregate lender commitments of $1.3 billion, and a maturity date of April 12, 2018.  The borrowing base is subject to regular semi-annual redeterminations. On October 6, 2014, the lending group redetermined the Company’s borrowing base under the credit facility and increased it from $2.2 billion to $2.4 billion, with no change in the aggregate lender commitments of $1.3 billion. The borrowing base redetermination process under the credit facility considers the value of the Company’s proved oil and gas properties, as determined by the lender group. The next scheduled redetermination date is April 1, 2015. Borrowings under the facility are secured by at least 75 percent of the Company’s proved oil and gas properties.
	The Company must comply with certain financial and non-financial covenants under the terms of its credit facility agreement, including limitations on the payment of dividends to $50.0 million per year.  The Company was in compliance with all covenants under the credit facility as of September 30, 2014, and through the filing date of this report.
	The following table presents the outstanding balance, total amount of letters of credit, and available borrowing capacity under the Company’s credit facility as of October 22, 2014, September 30, 2014, and December 31, 2013:
		As of October 22, 2014		As of September 30, 2014		As of December 31, 2013
		(in thousands)
	Credit facility balance	$	558,500	$	390,000	$	—
	Letters of credit (1)	$	808	$	808	$	808
	Available borrowing capacity	$	740,692	$	909,192	$	1,299,192
	____________________________________________
	(1) Letters of credit reduce the available borrowing capacity under the credit facility on a dollar-for-dollar basis.
	Senior Notes
	The Senior Notes line on the accompanying balance sheets represents the outstanding principal amount of the 6.625% Senior Notes due 2019 (the “2019 Notes”), the 6.50% Senior Notes due 2021 (the “2021 Notes”), the 6.50% Senior Notes due 2023 (the “2023 Notes”), and the 5.0% Senior Notes due 2024 (the “2024 Notes” and collectively with the 2019 Notes, 2021 Notes, and 2023 Notes, the “Senior Notes”), as shown in the table below:
		As of September 30, 2014		As of December 31, 2013
		(in thousands)
	2019 Notes	$	350,000	$	350,000
	2021 Notes	350,000		350,000
	2023 Notes	400,000		400,000
	2024 Notes	500,000		500,000
	Total Senior Notes	$	1,600,000	$	1,600,000
	The Senior Notes are unsecured senior obligations and rank equal in right of payment with all of the Company’s existing and any future unsecured senior debt, and are senior in right of payment to any future subordinated debt. There are no subsidiary guarantors of the Senior Notes.  The Company is subject to certain covenants under the respective indentures governing the Senior Notes that limit the Company’s ability to incur additional indebtedness, issue preferred stock, and make restricted payments, including dividends; provided, however, that the first $6.5 million of dividends paid each year are not restricted by these covenants. The Company does not expect these restrictions to limit its ability to continue paying dividends at its current rate for the foreseeable future if declared by the Company’s Board of Directors. The Company was in compliance with all covenants under its Senior Notes as of September 30, 2014, and through the filing date of this report.
	2024 Notes
	On May 20, 2013, the Company issued $500.0 million in aggregate principal amount of 2024 Notes. The 2024 Notes were issued at par and mature on January 15, 2024. Please refer to Note 5 - Long-term Debt in the Company’s 2013 Form 10-K for additional discussion of the terms of these notes.
	On May 20, 2013, the Company entered into a registration rights agreement that provided holders of the 2024 Notes certain registration rights under the Securities Act of 1933, as amended (the “Securities Act”). The Company closed its offer to exchange its 2024 Notes for notes registered under the Securities Act on June 25, 2014.

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	Note 6 - Commitments and Contingencies
	Commitments
	During the first nine months of 2014, the Company entered into drilling rig contracts with total expected commitments of $110.5 million and varying terms extending through 2016. As of September 30, 2014, the remaining expected drilling commitments totaled $72.3 million. Early termination of the remaining contracts would result in penalties totaling $42.5 million as of September 30, 2014. Subsequent to September 30, 2014, the Company entered into additional drilling rig contracts with future expected commitments totaling $24.5 million, and varying terms extending through 2016. Early termination of these contracts would result in penalties totaling $14.4 million.
	During the third quarter of 2014, as part of the Gooseneck prospect acquisition described in Note 3 - Acquisitions, Divestitures, and Assets Held for Sale, the Company assumed a share of the seller’s rights and obligations under a gas purchase agreement whereby the Company is subject to certain through-put commitments extending through 2028. The Company may be required to make periodic deficiency payments for any shortfalls in delivering the minimum applicable annual volume commitment. In the event that no product is delivered in accordance with this agreement, the undiscounted aggregate deficiency payments totaled approximately $24.4 million as of September 30, 2014. Subsequent to September 30, 2014, the Company closed an acquisition resulting in an increase it its obligations under this gas purchase agreement. As of the filing date of this report, in the event that no product is delivered in accordance with this agreement, the undiscounted aggregate deficiency payments total approximately $42.6 million. The Company expects to deliver at least the minimum applicable annual volumes under this agreement.
	Contingencies
	The Company is subject to litigation and claims arising in the ordinary course of business. The Company accrues for such items when a liability is both probable and the amount can be reasonably estimated. In the opinion of management, the results of such pending litigation and claims will not have a material effect on the results of operations, the financial position, or the cash flows of the Company.
	On April 16, 2014, the Company settled its previously disclosed litigation against Endeavour Operating Corporation (“Endeavour”). The Company, its working interest partners, and Endeavour agreed to mutually release all claims and dismiss the lawsuit in exchange for certain cash payments and other consideration paid to the Company and its working interest partners by Endeavour. The Company recorded a $10.7 million gain in the other operating revenues line item in the accompanying statements of operations in the second quarter of 2014 relating to this settlement.
	On January 27, 2011, Chieftain Royalty Company (“Chieftain”) filed a Class Action Petition against the Company in the District Court of Beaver County, Oklahoma, claiming damages related to royalty payments on all of the Oklahoma oil and gas wells operated by the Company and its predecessors. These claims include breach of contract, breach of fiduciary duty, fraud, unjust enrichment, tortious breach of contract, conspiracy, and conversion, based generally on asserted improper deduction of post-production costs. The Company removed this lawsuit to the United States District Court for the Western District of Oklahoma on February 22, 2011. The Company responded to the petition and denied the allegations. The district court did not rule on Chieftain’s motion to certify the putative class, and stayed all proceedings until the United States Court of Appeals for the Tenth Circuit issued its rulings on class certification in two similar royalty class action lawsuits. On July 9, 2013, the Tenth Circuit issued its opinions, reversing the trial courts’ grant of class certification and remanding the matters to the trial courts for those cases. The district court presiding over the Company’s case subsequently lifted its stay, and the Company now expects Chieftain to file a new motion for class certification in the first half of 2016.
	This case involves complex legal issues and uncertainties; a potentially large class of plaintiffs, and a large number of related producing properties, lease agreements and wells; and an alleged class period commencing in 1988 and spanning the entire producing life of the wells. Because the proceedings are in the early stages, with discovery yet to be completed, the Company is unable to estimate what impact, if any, the action will have on its financial condition, results of operations, or cash flows. The Company is still evaluating the claims, but believes that it has properly paid royalties under Oklahoma law and has and will continue to vigorously defend this case. On December 30, 2013, the Company sold a substantial portion of the assets that were subject to this matter and the buyer assumed any such liabilities related to such properties.

Compensation_Plans

Compensation Plans	9 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Compensation Plans	'
	Note 7 - Compensation Plans
	Cash Bonus Plan
	During the first nine months of 2014 and 2013, the Company paid $41.7 million and $16.0 million, respectively, for cash bonuses earned during the 2013 and 2012 performance years, respectively. The general and administrative (“G&A”) expense and exploration expense line items in the accompanying statements of operations include $6.2 million and $5.8 million of accrued cash bonus plan expense for the three months ended September 30, 2014, and 2013, respectively, and $19.0 million and $16.7 million of accrued cash bonus plan expense for the nine months ended September 30, 2014, and 2013, respectively, related to the respective performance years.
	Non-qualified Deferred Compensation Plan
	In January 2014, the Company established a non-qualified deferred compensation (“NQDC”) plan intended to provide plan participants with the ability to plan for income tax events and the opportunity to receive a benefit for matching contributions in excess of Internal Revenue Code (“IRC”) limits applicable to the Company’s 401(k) plan. The NQDC plan is designed to allow employee participants to defer a portion of base salary and cash bonuses paid pursuant to the Company’s cash bonus plan and director participants to defer a portion of the cash retainer paid to directors. Each year, participating employees may elect to defer (i) between 0% and 50% of their base salary and (ii) between 0% and 100% of the cash bonus paid pursuant to the cash bonus plan, and participating directors may elect to defer between 0% and 100% of their cash retainer. The NQDC plan requires the Company to make contributions for each eligible employee equal to 100% of the deferred amount for such employee, limited to 6% of such employee’s base salary and cash bonus. Each eligible employee’s interest in contributions made by the Company will vest 40% after the second year of such employee’s service to the Company, and 20% per year thereafter. A participant’s account will be distributed based upon the participant’s payment election made at the time of deferral. A participant may elect to have distributions made in lump sum or in annual installments ranging for a period from 1 to 10 years. Participants in the NQDC plan are currently limited to the Company’s officers and directors.
	Restricted Stock Units Under the Equity Incentive Compensation Plan
	The Company grants restricted stock units (“RSUs”) as part of its equity compensation program. Each RSU represents a right to one share of the Company’s common stock to be delivered upon settlement of the award at the end of the specified vesting period. Expense associated with RSUs is recognized as G&A expense and exploration expense over the vesting period of the award.
	Total expense recorded for RSUs for the three months ended September 30, 2014, and 2013, was $4.8 million and $3.7 million, respectively, and $10.5 million and $10.0 million for the nine months ended September 30, 2014, and 2013, respectively. As of September 30, 2014, there was $26.7 million of total unrecognized compensation expense related to unvested RSU awards, which is being amortized through 2017.
	A summary of the status and activity of non-vested RSUs for the nine-month period ended September 30, 2014, is presented in the following table:
		RSUs		Weighted-Average
				Grant-Date
				Fair Value
	Non-vested at beginning of year	580,431		$	57.05
	Granted	233,601		$	84.11
	Vested	(250,601	)	$	58.09
	Forfeited	(32,736	)	$	59.07
	Non-vested at end of quarter	530,695		$	68.34
	The fair value of the RSUs granted during the first nine months of 2014 was $19.6 million. These RSUs will vest 1/3rd on each of the next three anniversary dates of the grant. During the first nine months of 2014, the Company settled 250,601 RSUs that related to awards granted in previous years. The Company and the majority of grant participants mutually agreed to net share settle the awards to cover income and payroll tax withholdings as provided for in the plan document and award agreements. As a result, the Company issued 169,835 net shares of common stock. The remaining 80,766 shares were withheld to satisfy income and payroll tax withholding obligations that occurred upon delivery of the shares underlying those RSUs.
	Performance Share Units Under the Equity Incentive Compensation Plan
	The Company grants performance share units (“PSUs”) as part of its equity compensation program. The number of shares of the Company’s common stock issued to settle PSUs ranges from 0% to 200% of the number of PSUs awarded and is determined based on the Company’s performance over a three-year measurement period. The performance criteria for the PSUs are based on a combination of the Company’s annualized total shareholder return (“TSR”) for the measurement period and the relative performance of the Company’s TSR compared with the annualized TSRs of a group of peer companies for the measurement period. Expense associated with PSUs is recognized as G&A expense and exploration expense over the vesting period of the award.
	Total expense recorded for PSUs for the three months ended September 30, 2014, and 2013, was $4.8 million and $3.5 million, respectively, and $11.6 million and $13.2 million for the nine months ended September 30, 2014, and 2013, respectively. As of September 30, 2014, there was $24.7 million of total unrecognized compensation expense related to unvested PSU awards, which is being amortized through 2017.
	A summary of the status and activity of non-vested PSUs for the nine-month period ended September 30, 2014, is presented in the following table:
		PSUs (1)		Weighted-Average
				Grant-Date
				Fair Value
	Non-vested at beginning of year	572,469		$	66.07
	Granted	202,404		$	94.66
	Vested	(115,784	)	$	59.3
	Forfeited	(129,491	)	$	87.21
	Non-vested at end of quarter	529,598		$	73.31
	_______________________________________
	(1)	The number of awards assumes a one multiplier. The final number of shares of common stock issued may vary depending on the three-year performance multiplier, which ranges from zero to two.
	The fair value of the PSUs granted during the first nine months of 2014 was $19.2 million. These PSUs will vest on the third anniversary of the date of the grant. During the first nine months of 2014, the Company settled PSUs that were granted in 2011, which earned a 0.55 times multiplier, by issuing a net 85,121 shares of the Company’s common stock in accordance with the terms of the PSU awards. The Company and the majority of grant participants mutually agreed to net share settle the awards to cover income and payroll tax withholdings as provided for in the plan document and award agreements. As a result, the Company withheld 45,042 shares to satisfy income and payroll tax withholding obligations that occurred upon delivery of the shares underlying those PSUs.
	Stock Option Grants Under the Equity Incentive Compensation Plan
	A summary of activity associated with the Company’s Stock Option Plan for the nine months ended September 30, 2014, is presented in the following table:
		Shares		Weighted-			Aggregate
				Average			Intrinsic Value (in thousands)
				Exercise Price
	Outstanding, at beginning of year	39,088		$	20.87		$	2,433
	Exercised	(19,544	)	$	20.87		$	1,237
	Forfeited	—		$	—		$	—
	Outstanding, at end of quarter	19,544		$	20.87		$	1,117
	Vested and exercisable, at end of quarter	19,544		$	20.87		$	1,117
	As of September 30, 2014, there was no unrecognized compensation expense related to stock option awards.
	Director Shares
	During the nine months ended September 30, 2014 and 2013, the Company issued 27,677 and 28,169 shares, respectively, of its common stock to its non-employee directors, under the Company’s Equity Incentive Compensation Plan.  The Company recorded $196,000 of compensation expense related to these awards for the three months ended September 30, 2014, and no compensation expense related to these awards for the three months ended September 30, 2013. The Company recorded $1.4 million and $1.4 million of compensation expense related to these awards for the nine months ended September 30, 2014, and 2013, respectively.
	All shares of common stock issued to the Company’s non-employee directors are earned over the one-year service period following the date of grant, unless five years of service has been provided by the director, in which case that director's shares vest immediately.
	Employee Stock Purchase Plan
	Under the Company’s Employee Stock Purchase Plan (“ESPP”), eligible employees may purchase shares of the Company’s common stock through payroll deductions of up to 15 percent of eligible compensation, without accruing in excess of $25,000 in value from purchases for each calendar year. The purchase price of the stock is 85 percent of the lower of the fair market value of the stock on the first or last day of the purchase period, and shares issued under the ESPP have no restriction period. The ESPP is intended to qualify under Section 423 of the IRC. The Company had 1.2 million shares available for issuance under the ESPP as of September 30, 2014. The Company issued 35,249 and 44,437 shares under the ESPP during the first nine months of 2014 and 2013, respectively. The fair value of ESPP grants is measured at the date of grant using the Black-Scholes option-pricing model.
	Net Profits Interest Bonus Plan
	Cash payments made or accrued under the Company’s Net Profits Interest Bonus Plan (“Net Profits Plan”) that have been recorded as either G&A expense or exploration expense are presented in the table below:
		For the Three Months Ended September 30,						For the Nine Months Ended September 30,
		2014			2013			2014		2013
		(in thousands)
	General and administrative expense	$	2,487		$	4,302		$	7,451	$	11,531
	Exploration expense	162			329			644		1,026
	Total	$	2,649		$	4,631		$	8,095	$	12,557
	Additionally, the Company accrued or made cash payments under the Net Profits Plan of $8.3 million and $2.6 million for the nine months ended September 30, 2014, and 2013, respectively, as a result of divestiture proceeds. These cash payments are accounted for as a reduction in gain on divestiture activity included within the other operating revenues line in the accompanying statements of operations.

Pension_Benefits

Pension Benefits	9 Months Ended
	Sep. 30, 2014
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]	'
Pension Benefits	'
	Note 8 - Pension Benefits
	Pension Plans
	The Company has a non-contributory pension plan covering substantially all employees who meet age and service requirements (the “Qualified Pension Plan”). The Company also has a supplemental non-contributory pension plan covering certain management employees (the “Nonqualified Pension Plan” and together with the Qualified Pension Plan, the “Pension Plans”).
	Components of Net Periodic Benefit Cost for the Pension Plans
	The following table presents the components of the net periodic benefit cost for the Pension Plans:
		For the Three Months Ended September 30,						For the Nine Months Ended September 30,
		2014			2013			2014			2013
		(in thousands)
	Service cost	$	1,584		$	1,572		$	4,752		$	4,718
	Interest cost	548			407			1,643			1,220
	Expected return on plan assets that reduces periodic pension costs	(494		)	(384		)	(1,483		)	(1,153		)
	Amortization of prior service costs	4			4			13			13
	Amortization of net actuarial loss	172			306			516			917
	Net periodic benefit cost	$	1,814		$	1,905		$	5,441		$	5,715
	Prior service costs are amortized on a straight-line basis over the average remaining service period of active participants. Gains and losses in excess of 10 percent of the greater of the benefit obligation and the market-related value of assets are amortized over the average remaining service period of active participants.
	Contributions
	The Company contributed $5.3 million to the Pension Plans during the nine month period ended September 30, 2014.

Earnings_per_Share

Earnings per Share	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Earnings per Share	'
	Note 9 - Earnings per Share
	Basic net income per common share is calculated by dividing net income available to common stockholders by the basic weighted-average common shares outstanding for the respective period. The Company’s earnings per share calculations reflect the impact of any repurchases of shares of common stock made by the Company.
	Diluted net income per common share is calculated by dividing adjusted net income by the diluted weighted-average common shares outstanding, which includes the effect of potentially dilutive securities. Potentially dilutive securities for this calculation consist of in-the-money outstanding stock options, unvested RSUs, and contingent PSUs. The treasury stock method is used to measure the dilutive impact of unvested RSUs, contingent PSUs, and in-the-money stock options.
	PSUs represent the right to receive, upon settlement of the PSUs after completion of the three-year performance period, a number of shares of the Company’s common stock that may range from 0% to 200% of the number of PSUs granted on the award date. The number of potentially dilutive shares related to PSUs is based on the number of shares, if any, that would be issuable at the end of the respective reporting period, assuming that date was the end of the contingency period applicable to such PSUs. For additional discussion on PSUs, please refer to Note 7 - Compensation Plans under the heading Performance Share Units Under the Equity Incentive Compensation Plan.
	The following table sets forth the calculations of basic and diluted earnings per share:
		For the Three Months Ended September 30,				For the Nine Months Ended September 30,
		2014		2013		2014		2013
		(in thousands, except per share amounts)
	Net income	$	208,938	$	70,690	$	334,325	$	163,939
	Basic weighted-average common shares outstanding	67,379		66,943		67,169		66,486
	Add: dilutive effect of stock options, unvested RSUs, and contingent PSUs	1,051		1,310		1,089		1,483
	Diluted weighted-average common shares outstanding	68,430		68,253		68,258		67,969
	Basic net income per common share	$	3.1	$	1.06	$	4.98	$	2.47
	Diluted net income per common share	$	3.05	$	1.04	$	4.9	$	2.41

Derivative_Financial_Instrumen

Derivative Financial Instruments	9 Months Ended
	Sep. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative Financial Instruments	'
	Note 10 - Derivative Financial Instruments
	Summary of Oil, Gas, and NGL Derivative Contracts in Place
	The Company has entered into various commodity derivative contracts to mitigate a portion of its exposure to potentially adverse market changes in commodity prices and the associated impact on cash flows. All contracts are entered into for other-than-trading purposes. The Company’s derivative contracts include swap and costless collar arrangements for oil, gas, and NGLs.
	As of September 30, 2014, the Company had commodity derivative contracts outstanding through the second quarter of 2018 for a total of 17.6 million Bbls of oil production, 164.1 million MMBtu of gas production, and 1.8 million Bbls of NGL production.
	In a typical commodity swap agreement, if the agreed upon published third-party index price (“index price”) is lower than the swap fixed price, the Company receives the difference between the index price and the agreed upon swap fixed price. If the index price is higher than the swap fixed price, the Company pays the difference.  For collar agreements, the Company receives the difference between an index price and the floor price if the index price is below the floor price.  The Company pays the difference between the ceiling price and the index price if the index price is above the ceiling price.  No amounts are paid or received if the index price is between the floor and ceiling prices.
	The following tables summarize the approximate volumes and average contract prices of contracts the Company had in place as of September 30, 2014:
	Oil Contracts
	Oil Swaps
	Contract Period		NYMEX WTI Volumes			Weighted-Average
						Contract Price
			(Bbls)			(per Bbl)
	Fourth quarter 2014		2,016,000			$	96.01
	2015		5,741,000			$	91.14
	2016		5,570,000			$	88.01
	All oil swaps		13,327,000
	Oil Collars
	Contract Period		NYMEX WTI			Weighted-				Weighted-
			Volumes			Average Floor				Average Ceiling
						Price				Price
			(Bbls)			(per Bbl)				(per Bbl)
	Fourth quarter 2014		923,000			$	85			$	102.63
	2015		3,366,000			$	85			$	94.25
	All oil collars		4,289,000
	Gas Contracts
	Gas Swaps
	Contract Period		Volumes			Weighted-Average
						Contract Price
			(MMBtu)			(per MMBtu)
	Fourth quarter 2014		22,014,000			$	4.02
	2015		57,943,000			$	4.04
	2016		37,472,000			$	4.17
	2017		23,430,000			$	4.21
	2018		10,200,000			$	4.31
	All gas swaps*		151,059,000
	*Gas swaps are comprised of IF El Paso Permian (4%), IF HSC (83%), IF NGPL TXOK (2%), IF NNG Ventura (2%), IF Enable East (8%), and IF CIG (1%).
	Gas Collars
	Contract Period		Volumes			Weighted-				Weighted-
						Average Floor				Average Ceiling
						Price				Price
			(MMBtu)			(per MMBtu)				(per MMBtu)
	2015		13,002,000			$	3.98			$	4.3
	All gas collars*		13,002,000
	*Gas collars are comprised of IF El Paso Permian (4%), IF HSC (80%), IF NNG Ventura (8%), and IF Enable East (8%).
	NGL Contracts
	NGL Swaps
	Contract Period		Volumes			Weighted-Average
						Contract Price
			(Bbls)			(per Bbl)
	Fourth quarter 2014		980,000			$	61.69
	2015		781,000			$	55.42
	All NGL swaps*		1,761,000
	*NGL swaps are comprised of Oil Price Information System (“OPIS”) Mont Belvieu LDH Propane (67%) and OPIS Mont Belvieu NON-LDH Natural Gasoline (33%).
	Derivative Assets and Liabilities Fair Value
	The Company’s commodity derivatives are measured at fair value and are included in the accompanying balance sheets as derivative assets and liabilities. The fair value of the commodity derivative contracts was a net asset of $50.9 million and net asset of $21.5 million as of September 30, 2014, and December 31, 2013, respectively.
	The following tables detail the fair value of derivatives recorded in the accompanying balance sheets, by category:
		As of September 30, 2014
		Derivative Assets						Derivative Liabilities
		Balance Sheet		Fair Value				Balance Sheet		Fair Value
		Classification						Classification
		(in thousands)
	Commodity contracts	Current assets		$	41,295			Current liabilities		$	4,649
	Commodity contracts	Noncurrent assets		22,510				Noncurrent liabilities		8,243
	Derivatives not designated as hedging instruments			$	63,805					$	12,892
	As of December 31, 2013
	Derivative Assets						Derivative Liabilities
	Balance Sheet		Fair Value				Balance Sheet		Fair Value
	Classification						Classification
	(in thousands)
Commodity contracts	Current assets		$	21,559			Current liabilities		$	26,380
Commodity contracts	Noncurrent assets		30,951				Noncurrent liabilities		4,640
Derivatives not designated as hedging instruments			$	52,510					$	31,020
Offsetting of Derivative Assets and Liabilities
As of September 30, 2014, and December 31, 2013, all derivative instruments held by the Company were subject to enforceable master netting arrangements by various financial institutions. In general, the terms of the Company’s agreements provide for offsetting of amounts payable or receivable between it and the counterparty, at the election of both parties, for settlements that occur on the same date and in the same currency. The Company’s agreements also provide that in the event of an early termination, the counterparties have the right to offset amounts owed or owing under that and any other agreement with the same counterparty. The Company’s accounting policy is to not offset these positions in its accompanying balance sheets.
The following table provides a reconciliation between the gross assets and liabilities reflected on the accompanying balance sheets and the potential effects of master netting arrangements on the fair value of the Company’s derivative contracts:
		Derivative Assets								Derivative Liabilities
		As of								As of
Offsetting of Derivative Assets and Liabilities		September 30, 2014				December 31, 2013				September 30, 2014				December 31, 2013
		(in thousands)
Gross amounts presented in the accompanying balance sheets		$	63,805			$	52,510			$	(12,892	)		$	(31,020	)
Amounts not offset in the accompanying balance sheets		(12,744		)		(30,652		)		12,744				30,652
Net amounts		$	51,061			$	21,858			$	(148	)		$	(368	)
The following table summarizes the components of the derivative (gain) loss presented in the accompanying statements of operations:
	For the Three Months Ended September 30,								For the Nine Months Ended September 30,
	2014				2013				2014				2013
	(in thousands)
Derivative cash settlement (gain) loss:
Oil contracts	$	517			$	13,538			27,435				$	13,786
Gas contracts	1,687				(11,019		)		28,563				(18,752		)
NGL contracts	(1,930		)		(1,231		)		6,896				(7,749		)
Total derivative cash settlement (gain) loss(1)	274				1,288				62,894				(12,715		)
Derivative (gain) loss:
Oil contracts	(141,429		)		30,488				(42,802		)		8,233
Gas contracts	(43,039		)		(2,264		)		17,700				(12,462		)
NGL contracts	(6,467		)		10,421				(4,322		)		2,259
Total derivative (gain) loss (2)	$	(190,661	)		$	39,933			$	33,470			$	(14,685	)
____________________________________________
(1)	Total derivative cash settlement (gain) loss is reported in the derivative cash settlement gain (loss) line item on the condensed consolidated statements of cash flows within net cash provided by operating activities.
(2)	Total derivative (gain) loss is reported in the derivative (gain) loss line item on the condensed consolidated statements of cash flows within net cash provided by operating activities.
Credit Related Contingent Features
As of September 30, 2014, and through the filing date of this report, all of the Company’s derivative counterparties were members of the Company’s credit facility lender group. The Company’s obligations under its derivative contracts are secured by liens on at least 75 percent of the Company’s proved oil and gas properties.

Fair_Value_Measurements_Fair_V

Fair Value Measurements Fair Value Measurements	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Disclosures [Text Block]	'
	Note 11 - Fair Value Measurements
	The Company follows fair value measurement authoritative accounting guidance for all assets and liabilities measured at fair value. That authoritative accounting guidance defines fair value as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. Market or observable inputs are the preferred sources of values, followed by assumptions based on hypothetical transactions in the absence of market inputs. The fair value hierarchy for grouping these assets and liabilities is based on the significance level of the following inputs:
	•	Level 1 – quoted prices in active markets for identical assets or liabilities
	•	Level 2 – quoted prices in active markets for similar assets or liabilities, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations whose inputs are observable or whose significant value drivers are observable
	•	Level 3 – significant inputs to the valuation model are unobservable
	The following is a listing of the Company’s assets and liabilities that are measured at fair value and their classification within the fair value hierarchy as of September 30, 2014:
		Level 1			Level 2		Level 3
		(in thousands)
	Assets:
	Derivatives (1)	$	—		$	63,805	$	—
	Proved oil and gas properties (2)	$	—		$	—	$	9,443
	Unproved oil and gas properties (2)	$	—		$	—	$	43,252
	Oil and gas properties held for sale (2)	$	—		$	—	$	17,952
	Liabilities:
	Derivatives (1)	$	—		$	12,892	$	—
	Net Profits Plan (1)	$	—		$	—	$	41,705
	Asset retirement obligation (2)	$	—		$	—	$	923
	Asset retirement obligation associated with oil and gas properties held for sale (2)	$	—		$	—	$	452
	____________________________________________
	(1) This represents a financial asset or liability that is measured at fair value on a recurring basis.
	(2) This represents a non-financial asset or liability that is measured at fair value on a nonrecurring basis.
	The following is a listing of the Company’s assets and liabilities that are measured at fair value and their classification within the fair value hierarchy as of December 31, 2013:
		Level 1			Level 2		Level 3
		(in thousands)
	Assets:
	Derivatives (1)	$	—		$	52,510	$	—
	Proved oil and gas properties (2)	$	—		$	—	$	62,178
	Unproved oil and gas properties (2)	$	—		$	—	$	3,280
	Oil and gas properties held for sale (2)	$	—		$	—	$	650
	Liabilities:
	Derivatives (1)	$	—		$	31,020	$	—
	Net Profits Plan (1)	$	—		$	—	$	56,985
	____________________________________________
	(1) This represents a financial asset or liability that is measured at fair value on a recurring basis.
	(2) This represents a non-financial asset or liability that is measured at fair value on a nonrecurring basis.
	Both financial and non-financial assets and liabilities are categorized within the above fair value hierarchy based on the lowest level of input that is significant to the fair value measurement. The following is a description of the valuation methodologies used by the Company as well as the general classification of such instruments pursuant to the above fair value hierarchy.
	Derivatives
	The Company uses Level 2 inputs to measure the fair value of oil, gas, and NGL commodity derivatives. Fair values are based upon interpolated data. The Company derives internal valuation estimates taking into consideration the counterparties’ credit ratings, the Company’s credit rating, and the time value of money. These valuations are then compared to the respective counterparties’ mark-to-market statements. These factors result in an estimated exit-price that management believes provides a reasonable and consistent methodology for valuing derivative instruments. The derivative instruments utilized by the Company are not considered by management to be complex, structured, or illiquid. The oil, gas, and NGL commodity derivative markets are highly active.
	Generally, market quotes assume that all counterparties have near zero, or low, default rates and have equal credit quality. However, an adjustment may be necessary to reflect the credit quality of a specific counterparty to determine the fair value of the instrument. The Company monitors the credit ratings of its counterparties and may require counterparties to post collateral if their ratings deteriorate. In some instances, the Company will attempt to novate the trade to a more stable counterparty.
	Valuation adjustments are necessary to reflect the effect of the Company’s credit quality on the fair value of any liability position with a counterparty. This adjustment takes into account any credit enhancements, such as collateral margin that the Company may have posted with a counterparty, as well as any letters of credit between the parties. The methodology to determine this adjustment is consistent with how the Company evaluates counterparty credit risk, taking into account the Company’s credit rating, current credit facility margins, and any change in such margins since the last measurement date. All of the Company’s derivative counterparties are members of the Company’s credit facility lender group.
	The methods described above may result in a fair value estimate that may not be indicative of net realizable value or may not be reflective of future fair values and cash flows. While the Company believes that the valuation methods utilized are appropriate and consistent with authoritative accounting guidance and with other marketplace participants, the Company recognizes that third parties may use different methodologies or assumptions to determine the fair value of certain financial instruments that could result in a different estimate of fair value at the reporting date.
	Refer to Note 10 - Derivative Financial Instruments for more information regarding the Company’s derivative instruments.
	Net Profits Plan
	The Net Profits Plan is a standalone liability for which there is no available market price, principal market, or market participants. The inputs available for this instrument are unobservable and are therefore classified as Level 3 inputs. The Company employs the income approach, which converts expected future cash flow amounts to a single present value amount. This technique uses the estimate of future cash payments, expectations of possible variations in the amount and/or timing of cash flows, the risk premium, and nonperformance risk to calculate the fair value. There is a direct correlation between realized oil, gas, and NGL commodity prices driving net cash flows and the Net Profits Plan liability. Generally, higher commodity prices result in a larger Net Profits Plan liability and lower commodity prices result in a smaller Net Profits Plan liability.
	The Company records the estimated fair value of the long-term liability for estimated future payments under the Net Profits Plan based on the discounted value of estimated future payments associated with each individual pool. The calculation of this liability is a significant management estimate. A discount rate of 12 percent is used to calculate this liability and is intended to represent the Company’s best estimate of the present value of expected future payments under the Net Profits Plan.
	The Company’s estimate of its liability is highly dependent on commodity prices, cost assumptions, discount rates, and overall market conditions. The Company regularly assesses the current market environment.  The Net Profits Plan liability is determined using price assumptions of five one-year strip prices with the fifth year’s pricing then carried out indefinitely. The average price is adjusted for realized price differentials and to include the effects of the forecasted production covered by derivatives contracts in the relevant periods.  The non-cash expense associated with this significant management estimate is highly volatile from period to period due to fluctuations that occur in the oil, gas, and NGL commodity markets.
	If the commodity prices used in the calculation changed by five percent, the liability recorded at September 30, 2014, would differ by approximately $4 million. A one percent increase or decrease in the discount rate would result in a change of approximately $2 million. Actual cash payments to be made to participants in future periods are dependent on realized actual production, realized commodity prices, and costs associated with the properties in each individual pool of the Net Profits Plan. Consequently, actual cash payments are inherently different from the amounts estimated.
	No published market quotes exist on which to base the Company’s estimate of fair value of its Net Profits Plan liability. As such, the recorded fair value is based entirely on management estimates that are described within this footnote. While some inputs to the Company’s calculation of fair value on the Net Profits Plan’s future payments are from published sources, others, such as the discount rate and the expected future cash flows, are derived from the Company’s own calculations and estimates.
	The following table reflects the activity for the Company’s Net Profits Plan liability measured at fair value using Level 3 inputs:
		For the Nine Months Ended September 30, 2014
		(in thousands)
	Beginning balance	$	56,985
	Net increase in liability (1)	1,156
	Net settlements (1) (2)	(16,436		)
	Transfers in (out) of Level 3	—
	Ending balance	$	41,705
	____________________________________________
	(1)	Net changes in the Company’s Net Profits Plan liability are shown in the Change in Net Profits Plan liability line item of the accompanying statements of operations.
	(2)	Settlements represent cash payments made or accrued under the Net Profits Plan. The Company accrued or made cash payments under the Net Profits Plan of $8.3 million as a result of divestitures during the nine months ended September 30, 2014.
	Long-term Debt
	The following table reflects the fair value of the Senior Notes measured using Level 1 inputs based on quoted secondary market trading prices. The Senior Notes were not presented at fair value on the accompanying balance sheets as of September 30, 2014, or December 31, 2013, as they are recorded at historical value.
		As of September 30, 2014			As of December 31, 2013
		(in thousands)
2019 Notes	$	364,000		$	374,290
2021 Notes	$	371,875		$	373,625
2023 Notes	$	415,500		$	422,000
2024 Notes	$	492,500		$	475,315
As of September 30, 2014, the Company had $390.0 million of floating-rate debt outstanding. The carrying value of the Company’s credit facility approximates its fair value, as the applicable interest rates are floating and based on prevailing market rates.
Proved and Unproved Oil and Gas Properties
Proved oil and gas property costs are evaluated for impairment and reduced to fair value when there is an indication that the carrying costs may not be recoverable. The Company uses Level 3 inputs and the income valuation technique, which converts future amounts to a single present value amount, to measure the fair value of proved properties through an application of discount rates and price forecasts selected by the Company’s management. The calculation of the discount rate is based on the best information available and was estimated to be 12 percent as of September 30, 2014, and December 31, 2013. The Company believes that the discount rate is representative of current market conditions and takes into account estimates of future cash payments, expectations of possible variations in the amount and/or timing of cash flows, the risk premium, and nonperformance risk. The prices for oil and gas are forecasted based on New York Mercantile Exchange (“NYMEX”) strip pricing, adjusted for basis differentials, for the first five years, after which a flat terminal price is used for each commodity stream. The prices for NGLs are forecasted using OPIS Mont Belvieu pricing, for as long as the market is actively trading, after which a flat terminal price is used. Future operating costs are also adjusted as deemed appropriate for these estimates. Proved properties classified as held for sale are valued using a market approach, based on an estimated selling price, as evidenced by the most current bid prices received from third parties. If an estimated selling price is not available, the Company utilizes the income valuation technique discussed above.
Unproved oil and gas property costs are evaluated for impairment and reduced to fair value when there is an indication that the carrying costs may not be recoverable.  To measure the fair value of unproved properties, the Company uses a market approach, which takes into account the following significant assumptions: future development plans, risk weighted potential resource recovery, and estimated reserve values. Unproved properties classified as held for sale are valued using a market approach, based on an estimated selling price, as evidenced by the most current bid prices received from third parties. If an estimated selling price is not available, the Company estimates acreage value based on the price received for similar acreage in recent transactions by the Company or other market participants in the principal market.
The fair value measurements of assets acquired and liabilities assumed are measured on a nonrecurring basis on the acquisition date using an income valuation technique based on inputs that are not observable in the market and therefore represent Level 3 inputs. Significant inputs to the valuation of acquired oil and gas properties include estimates of: (i) reserves; (ii) production rates; (iii) future operating and development costs; (iv) future commodity prices, including price differentials; (v) future cash flows; and (vi) a market participant-based weighted average cost of capital rate. These inputs require significant judgments and estimates by the Company’s management at the time of the valuation and are subject to change. Refer to Note 3 - Acquisitions, Divestiture, and Assets Held for Sale for additional information on the fair value of assets acquired during the nine months ended September 30, 2014.
Asset Retirement Obligations
The Company utilizes the income valuation technique to determine the fair value of the asset retirement obligation liability at the point of inception by applying a credit-adjusted risk-free rate, which takes into account the Company’s credit risk, the time value of money, and the current economic state, to the undiscounted expected abandonment cash flows. Given the unobservable nature of the inputs, the initial measurement of the asset retirement obligation liability is deemed to use Level 3 inputs.

Basis_of_Presentation_Signific1

Basis of Presentation, Significant Accounting Policies, and Recently Issued Accounting Standards (Policies)	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Non-qualified Deferred Compensation Plan [Policy Text Block]	'
	Non-qualified Deferred Compensation Plan
	In January 2014, the Company established a non-qualified deferred compensation (“NQDC”) plan intended to provide plan participants with the ability to plan for income tax events and the opportunity to receive a benefit for matching contributions in excess of Internal Revenue Code (“IRC”) limits applicable to the Company’s 401(k) plan. The NQDC plan is designed to allow employee participants to defer a portion of base salary and cash bonuses paid pursuant to the Company’s cash bonus plan and director participants to defer a portion of the cash retainer paid to directors. Each year, participating employees may elect to defer (i) between 0% and 50% of their base salary and (ii) between 0% and 100% of the cash bonus paid pursuant to the cash bonus plan, and participating directors may elect to defer between 0% and 100% of their cash retainer. The NQDC plan requires the Company to make contributions for each eligible employee equal to 100% of the deferred amount for such employee, limited to 6% of such employee’s base salary and cash bonus. Each eligible employee’s interest in contributions made by the Company will vest 40% after the second year of such employee’s service to the Company, and 20% per year thereafter. A participant’s account will be distributed based upon the participant’s payment election made at the time of deferral. A participant may elect to have distributions made in lump sum or in annual installments ranging for a period from 1 to 10 years. Participants in the NQDC plan are currently limited to the Company’s officers and directors.
Description and terms of the Performance Share Awards	'
	Performance Share Units Under the Equity Incentive Compensation Plan
	The Company grants performance share units (“PSUs”) as part of its equity compensation program. The number of shares of the Company’s common stock issued to settle PSUs ranges from 0% to 200% of the number of PSUs awarded and is determined based on the Company’s performance over a three-year measurement period. The performance criteria for the PSUs are based on a combination of the Company’s annualized total shareholder return (“TSR”) for the measurement period and the relative performance of the Company’s TSR compared with the annualized TSRs of a group of peer companies for the measurement period. Expense associated with PSUs is recognized as G&A expense and exploration expense over the vesting period of the award.
Fair value of financial instruments measured on a recurring Basis	'
	The Company uses Level 2 inputs to measure the fair value of oil, gas, and NGL commodity derivatives. Fair values are based upon interpolated data. The Company derives internal valuation estimates taking into consideration the counterparties’ credit ratings, the Company’s credit rating, and the time value of money. These valuations are then compared to the respective counterparties’ mark-to-market statements. These factors result in an estimated exit-price that management believes provides a reasonable and consistent methodology for valuing derivative instruments. The derivative instruments utilized by the Company are not considered by management to be complex, structured, or illiquid. The oil, gas, and NGL commodity derivative markets are highly active.
	Generally, market quotes assume that all counterparties have near zero, or low, default rates and have equal credit quality. However, an adjustment may be necessary to reflect the credit quality of a specific counterparty to determine the fair value of the instrument. The Company monitors the credit ratings of its counterparties and may require counterparties to post collateral if their ratings deteriorate. In some instances, the Company will attempt to novate the trade to a more stable counterparty.
	Valuation adjustments are necessary to reflect the effect of the Company’s credit quality on the fair value of any liability position with a counterparty. This adjustment takes into account any credit enhancements, such as collateral margin that the Company may have posted with a counterparty, as well as any letters of credit between the parties. The methodology to determine this adjustment is consistent with how the Company evaluates counterparty credit risk, taking into account the Company’s credit rating, current credit facility margins, and any change in such margins since the last measurement date. All of the Company’s derivative counterparties are members of the Company’s credit facility lender group.
	The methods described above may result in a fair value estimate that may not be indicative of net realizable value or may not be reflective of future fair values and cash flows. While the Company believes that the valuation methods utilized are appropriate and consistent with authoritative accounting guidance and with other marketplace participants, the Company recognizes that third parties may use different methodologies or assumptions to determine the fair value of certain financial instruments that could result in a different estimate of fair value at the reporting date.
	Refer to Note 10 - Derivative Financial Instruments for more information regarding the Company’s derivative instruments.

Assets_Held_for_Sale_Fair_Valu

Assets Held for Sale Fair Value of Net Assets Acquired from Baytex (Tables)	9 Months Ended
	Sep. 30, 2014
Fair Value of Net Assets Acquired from Baytex [Abstract]	'
Schedule of Fair Value of Net Assets Acquired [Table Text Block]	'
	Purchase Price	As of September 24, 2014
		(in thousands)
	Cash consideration	$	325,230
	Fair value of assets acquired:
	Proved oil and gas properties	$	201,842
	Unproved oil and gas properties	125,562
	Total fair value of oil and gas properties acquired	327,404
	Working capital	(61		)
	Asset retirement obligation	(2,113		)
	Total fair value of net assets acquired	$	325,230

Income_Taxes_Tables

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2014
Income Tax Disclosure [Abstract]	'
Schedule of provision for income taxes	'
	The provision for income taxes consists of the following:
		For the Three Months Ended September 30,						For the Nine Months Ended September 30,
		2014			2013			2014			2013
		(in thousands)
	Current portion of income tax (benefit) expense:
	Federal	$	—		$	—		$	—		$	—
	State	479			(46		)	1,480			302
	Deferred portion of income tax expense	124,269			42,380			198,180			98,619
	Total income tax expense	$	124,748		$	42,334		$	199,660		$	98,921
		37.4		%	37.5		%	37.4		%	37.6		%

LongTerm_Debt_Tables

Long-Term Debt (Tables)	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Schedule of Long-term Debt Instruments [Table Text Block]	'
	The following table presents the outstanding balance, total amount of letters of credit, and available borrowing capacity under the Company’s credit facility as of October 22, 2014, September 30, 2014, and December 31, 2013:
		As of October 22, 2014		As of September 30, 2014		As of December 31, 2013
		(in thousands)
	Credit facility balance	$	558,500	$	390,000	$	—
	Letters of credit (1)	$	808	$	808	$	808
	Available borrowing capacity	$	740,692	$	909,192	$	1,299,192
	____________________________________________
	(1) Letters of credit reduce the available borrowing capacity under the credit facility on a dollar-for-dollar basis.
	The Senior Notes line on the accompanying balance sheets represents the outstanding principal amount of the 6.625% Senior Notes due 2019 (the “2019 Notes”), the 6.50% Senior Notes due 2021 (the “2021 Notes”), the 6.50% Senior Notes due 2023 (the “2023 Notes”), and the 5.0% Senior Notes due 2024 (the “2024 Notes” and collectively with the 2019 Notes, 2021 Notes, and 2023 Notes, the “Senior Notes”), as shown in the table below:
		As of September 30, 2014		As of December 31, 2013
		(in thousands)
	2019 Notes	$	350,000	$	350,000
	2021 Notes	350,000		350,000
	2023 Notes	400,000		400,000
	2024 Notes	500,000		500,000
	Total Senior Notes	$	1,600,000	$	1,600,000

Compensation_Plans_Tables

Compensation Plans (Tables)	9 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]	'
	Stock Option Grants Under the Equity Incentive Compensation Plan
	A summary of activity associated with the Company’s Stock Option Plan for the nine months ended September 30, 2014, is presented in the following table:
		Shares		Weighted-			Aggregate
				Average			Intrinsic Value (in thousands)
				Exercise Price
	Outstanding, at beginning of year	39,088		$	20.87		$	2,433
	Exercised	(19,544	)	$	20.87		$	1,237
	Forfeited	—		$	—		$	—
	Outstanding, at end of quarter	19,544		$	20.87		$	1,117
	Vested and exercisable, at end of quarter	19,544		$	20.87		$	1,117
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]	'
	A summary of the status and activity of non-vested RSUs for the nine-month period ended September 30, 2014, is presented in the following table:
		RSUs		Weighted-Average
				Grant-Date
				Fair Value
	Non-vested at beginning of year	580,431		$	57.05
	Granted	233,601		$	84.11
	Vested	(250,601	)	$	58.09
	Forfeited	(32,736	)	$	59.07
	Non-vested at end of quarter	530,695		$	68.34
Share-based Compensation, Performance Shares Award Outstanding Activity [Table Text Block]	'
	A summary of the status and activity of non-vested PSUs for the nine-month period ended September 30, 2014, is presented in the following table:
		PSUs (1)		Weighted-Average
				Grant-Date
				Fair Value
	Non-vested at beginning of year	572,469		$	66.07
	Granted	202,404		$	94.66
	Vested	(115,784	)	$	59.3
	Forfeited	(129,491	)	$	87.21
	Non-vested at end of quarter	529,598		$	73.31
	_______________________________________
	(1)	The number of awards assumes a one multiplier. The final number of shares of common stock issued may vary depending on the three-year performance multiplier, which ranges from zero to two.
Schedule of Net Profits Plan Cash Payment Allocation	'
	Cash payments made or accrued under the Company’s Net Profits Interest Bonus Plan (“Net Profits Plan”) that have been recorded as either G&A expense or exploration expense are presented in the table below:
		For the Three Months Ended September 30,						For the Nine Months Ended September 30,
		2014			2013			2014		2013
		(in thousands)
	General and administrative expense	$	2,487		$	4,302		$	7,451	$	11,531
	Exploration expense	162			329			644		1,026
	Total	$	2,649		$	4,631		$	8,095	$	12,557

Pension_Benefits_Tables

Pension Benefits (Tables)	9 Months Ended
	Sep. 30, 2014
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]	'
Components of the net periodic benefit cost for both the Qualified and the Nonqualified Pension Plan	'
	The following table presents the components of the net periodic benefit cost for the Pension Plans:
		For the Three Months Ended September 30,						For the Nine Months Ended September 30,
		2014			2013			2014			2013
		(in thousands)
	Service cost	$	1,584		$	1,572		$	4,752		$	4,718
	Interest cost	548			407			1,643			1,220
	Expected return on plan assets that reduces periodic pension costs	(494		)	(384		)	(1,483		)	(1,153		)
	Amortization of prior service costs	4			4			13			13
	Amortization of net actuarial loss	172			306			516			917
	Net periodic benefit cost	$	1,814		$	1,905		$	5,441		$	5,715

Earnings_per_Share_Tables

Earnings per Share (Tables)	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Schedule of calculation of basic and diluted earnings per share	'
	The following table sets forth the calculations of basic and diluted earnings per share:
		For the Three Months Ended September 30,				For the Nine Months Ended September 30,
		2014		2013		2014		2013
		(in thousands, except per share amounts)
	Net income	$	208,938	$	70,690	$	334,325	$	163,939
	Basic weighted-average common shares outstanding	67,379		66,943		67,169		66,486
	Add: dilutive effect of stock options, unvested RSUs, and contingent PSUs	1,051		1,310		1,089		1,483
	Diluted weighted-average common shares outstanding	68,430		68,253		68,258		67,969
	Basic net income per common share	$	3.1	$	1.06	$	4.98	$	2.47
	Diluted net income per common share	$	3.05	$	1.04	$	4.9	$	2.41

Derivative_Financial_Instrumen1

Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]	'
	The following tables summarize the approximate volumes and average contract prices of contracts the Company had in place as of September 30, 2014:
	Oil Contracts
	Oil Swaps
	Contract Period		NYMEX WTI Volumes			Weighted-Average
						Contract Price
			(Bbls)			(per Bbl)
	Fourth quarter 2014		2,016,000			$	96.01
	2015		5,741,000			$	91.14
	2016		5,570,000			$	88.01
	All oil swaps		13,327,000
	Oil Collars
	Contract Period		NYMEX WTI			Weighted-				Weighted-
			Volumes			Average Floor				Average Ceiling
						Price				Price
			(Bbls)			(per Bbl)				(per Bbl)
	Fourth quarter 2014		923,000			$	85			$	102.63
	2015		3,366,000			$	85			$	94.25
	All oil collars		4,289,000
	Gas Contracts
	Gas Swaps
	Contract Period		Volumes			Weighted-Average
						Contract Price
			(MMBtu)			(per MMBtu)
	Fourth quarter 2014		22,014,000			$	4.02
	2015		57,943,000			$	4.04
	2016		37,472,000			$	4.17
	2017		23,430,000			$	4.21
	2018		10,200,000			$	4.31
	All gas swaps*		151,059,000
	*Gas swaps are comprised of IF El Paso Permian (4%), IF HSC (83%), IF NGPL TXOK (2%), IF NNG Ventura (2%), IF Enable East (8%), and IF CIG (1%).
	Gas Collars
	Contract Period		Volumes			Weighted-				Weighted-
						Average Floor				Average Ceiling
						Price				Price
			(MMBtu)			(per MMBtu)				(per MMBtu)
	2015		13,002,000			$	3.98			$	4.3
	All gas collars*		13,002,000
	*Gas collars are comprised of IF El Paso Permian (4%), IF HSC (80%), IF NNG Ventura (8%), and IF Enable East (8%).
	NGL Contracts
	NGL Swaps
	Contract Period		Volumes			Weighted-Average
						Contract Price
			(Bbls)			(per Bbl)
	Fourth quarter 2014		980,000			$	61.69
	2015		781,000			$	55.42
	All NGL swaps*		1,761,000
	*NGL swaps are comprised of Oil Price Information System (“OPIS”) Mont Belvieu LDH Propane (67%) and OPIS Mont Belvieu NON-LDH Natural Gasoline (33%).
Schedule of fair value of derivatives in accompanying balance sheets	'
	The following tables detail the fair value of derivatives recorded in the accompanying balance sheets, by category:
		As of September 30, 2014
		Derivative Assets						Derivative Liabilities
		Balance Sheet		Fair Value				Balance Sheet		Fair Value
		Classification						Classification
		(in thousands)
	Commodity contracts	Current assets		$	41,295			Current liabilities		$	4,649
	Commodity contracts	Noncurrent assets		22,510				Noncurrent liabilities		8,243
	Derivatives not designated as hedging instruments			$	63,805					$	12,892
		As of December 31, 2013
		Derivative Assets						Derivative Liabilities
		Balance Sheet		Fair Value				Balance Sheet		Fair Value
		Classification						Classification
		(in thousands)
	Commodity contracts	Current assets		$	21,559			Current liabilities		$	26,380
	Commodity contracts	Noncurrent assets		30,951				Noncurrent liabilities		4,640
	Derivatives not designated as hedging instruments			$	52,510					$	31,020
Schedule of the potential effects of master netting arrangements [Table Text Block]	'
	The following table provides a reconciliation between the gross assets and liabilities reflected on the accompanying balance sheets and the potential effects of master netting arrangements on the fair value of the Company’s derivative contracts:
			Derivative Assets								Derivative Liabilities
			As of								As of
	Offsetting of Derivative Assets and Liabilities		September 30, 2014				December 31, 2013				September 30, 2014				December 31, 2013
			(in thousands)
	Gross amounts presented in the accompanying balance sheets		$	63,805			$	52,510			$	(12,892	)		$	(31,020	)
	Amounts not offset in the accompanying balance sheets		(12,744		)		(30,652		)		12,744				30,652
	Net amounts		$	51,061			$	21,858			$	(148	)		$	(368	)
Schedule of derivative (gain) loss	'
	The following table summarizes the components of the derivative (gain) loss presented in the accompanying statements of operations:
		For the Three Months Ended September 30,								For the Nine Months Ended September 30,
		2014				2013				2014				2013
		(in thousands)
	Derivative cash settlement (gain) loss:
	Oil contracts	$	517			$	13,538			27,435				$	13,786
	Gas contracts	1,687				(11,019		)		28,563				(18,752		)
	NGL contracts	(1,930		)		(1,231		)		6,896				(7,749		)
	Total derivative cash settlement (gain) loss(1)	274				1,288				62,894				(12,715		)
	Derivative (gain) loss:
	Oil contracts	(141,429		)		30,488				(42,802		)		8,233
	Gas contracts	(43,039		)		(2,264		)		17,700				(12,462		)
	NGL contracts	(6,467		)		10,421				(4,322		)		2,259
	Total derivative (gain) loss (2)	$	(190,661	)		$	39,933			$	33,470			$	(14,685	)
	____________________________________________
	(1)	Total derivative cash settlement (gain) loss is reported in the derivative cash settlement gain (loss) line item on the condensed consolidated statements of cash flows within net cash provided by operating activities.
	(2)	Total derivative (gain) loss is reported in the derivative (gain) loss line item on the condensed consolidated statements of cash flows within net cash provided by operating activities.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Table Text Block]	'
	The following is a listing of the Company’s assets and liabilities that are measured at fair value and their classification within the fair value hierarchy as of September 30, 2014:
		Level 1			Level 2		Level 3
		(in thousands)
	Assets:
	Derivatives (1)	$	—		$	63,805	$	—
	Proved oil and gas properties (2)	$	—		$	—	$	9,443
	Unproved oil and gas properties (2)	$	—		$	—	$	43,252
	Oil and gas properties held for sale (2)	$	—		$	—	$	17,952
	Liabilities:
	Derivatives (1)	$	—		$	12,892	$	—
	Net Profits Plan (1)	$	—		$	—	$	41,705
	Asset retirement obligation (2)	$	—		$	—	$	923
	Asset retirement obligation associated with oil and gas properties held for sale (2)	$	—		$	—	$	452
	____________________________________________
	(1) This represents a financial asset or liability that is measured at fair value on a recurring basis.
	(2) This represents a non-financial asset or liability that is measured at fair value on a nonrecurring basis.
	The following is a listing of the Company’s assets and liabilities that are measured at fair value and their classification within the fair value hierarchy as of December 31, 2013:
		Level 1			Level 2		Level 3
		(in thousands)
	Assets:
	Derivatives (1)	$	—		$	52,510	$	—
	Proved oil and gas properties (2)	$	—		$	—	$	62,178
	Unproved oil and gas properties (2)	$	—		$	—	$	3,280
	Oil and gas properties held for sale (2)	$	—		$	—	$	650
	Liabilities:
	Derivatives (1)	$	—		$	31,020	$	—
	Net Profits Plan (1)	$	—		$	—	$	56,985
	____________________________________________
	(1) This represents a financial asset or liability that is measured at fair value on a recurring basis.
	(2) This represents a non-financial asset or liability that is measured at fair value on a nonrecurring basis.
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]	'
	The following table reflects the activity for the Company’s Net Profits Plan liability measured at fair value using Level 3 inputs:
		For the Nine Months Ended September 30, 2014
		(in thousands)
	Beginning balance	$	56,985
	Net increase in liability (1)	1,156
	Net settlements (1) (2)	(16,436		)
	Transfers in (out) of Level 3	—
	Ending balance	$	41,705
	____________________________________________
	(1)	Net changes in the Company’s Net Profits Plan liability are shown in the Change in Net Profits Plan liability line item of the accompanying statements of operations.
	(2)	Settlements represent cash payments made or accrued under the Net Profits Plan. The Company accrued or made cash payments under the Net Profits Plan of $8.3 million as a result of divestitures during the nine months ended September 30, 2014.
Fair Value, by Balance Sheet Grouping [Table Text Block]	'
	The following table reflects the fair value of the Senior Notes measured using Level 1 inputs based on quoted secondary market trading prices. The Senior Notes were not presented at fair value on the accompanying balance sheets as of September 30, 2014, or December 31, 2013, as they are recorded at historical value.
		As of September 30, 2014			As of December 31, 2013
		(in thousands)
	2019 Notes	$	364,000		$	374,290
	2021 Notes	$	371,875		$	373,625
	2023 Notes	$	415,500		$	422,000
	2024 Notes	$	492,500		$	475,315

Assets_Held_for_Sale_Details

Assets Held for Sale (Details) (USD $)	9 Months Ended						9 Months Ended	3 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 24, 2014	Sep. 24, 2014	Oct. 15, 2014	Sep. 30, 2014	Jun. 30, 2014
				Gooseneck Prospect Acquisition [Member]	Gooseneck Prospect Acquisition [Member]	Gooseneck Prospect Acquisition [Member]	Rocky Mountain [Member]	Rocky Mountain [Member]
					Fair Value, Measurements, Nonrecurring [Member]	Subsequent Event [Member]
Business Acquisition [Line Items]	'	'	'	'	'	'	'	'
Net acres acquired	'	'	'	61,000	'	'	'	'
Cash Consideration to Acquire Proved and Unproved Property	'	'	'	$325,230,000	'	$84,800,000	'	'
Proved Oil and Gas Property, Successful Effort Method	6,789,927,000	'	5,637,462,000	'	201,842,000	'	'	'
Unproved Oil and Gas Property, Successful Effort Method	536,100,000	'	271,100,000	'	125,562,000	'	'	'
Oil and Gas Property, Successful Effort Method, Net	'	'	'	'	327,404,000	'	'	'
Working Capital Acquired	'	'	'	'	-61,000	'	'	'
Asset Retirement Obligations, Noncurrent	123,905,000	'	115,659,000	'	-2,113,000	'	'	'
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	'	'	'	'	325,230,000	'	'	'
Leasehold Acres Consideration to Acquire Unproved Property	'	'	'	'	'	'	7,000	'
Payments to Acquire Oil and Gas Property	'	'	'	'	'	'	134,100,000	'
Proceeds from Sale of Oil and Gas Property and Equipment	41,868,000	20,498,000	'	'	'	'	'	50,200,000
Gain (Loss) on Disposition of Oil and Gas Property	'	'	'	'	'	'	'	26,800,000
Assets Held-for-sale Reasonably Certain Period for Sale	1	'	'	'	'	'	'	'
Disposal Group, Including Discontinued Operation, Long Lived Assets, Current	19,900,000	'	'	'	'	'	'	'
Asset retirement obligation associated with oil and gas properties held for sale	$452,000	'	$3,033,000	'	'	'	'	'

Income_Taxes_Details

Income Taxes (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Components of the provision for income taxes	'	'	'	'
Federal	$0	$0	$0	$0
State	479	-46	1,480	302
Deferred portion of income tax expense	124,269	42,380	198,180	98,619
Income tax expense	$124,748	$42,334	$199,660	$98,921
Effective tax rate	37.40%	37.50%	37.40%	37.60%

Income_Taxes_Narrative_Details

Income Taxes Narrative (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014
Income Tax Narrative [Abstract]	'
IRS Proposed R&D Tax Adjustment	$4.60

LongTerm_Debt_Details

Long-Term Debt (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013	20-May-13	Oct. 06, 2014
			Line of Credit [Member]	5.0% Senior Notes Due 2024 [Member]	Senior Notes [Member]	Senior Notes [Member]	Senior Notes [Member]	Subsequent Event [Member]
								Line of Credit [Member]
Debt Instrument [Line Items]	'	'	'	'	'	'	'	'
Line of Credit Facility, Maximum Borrowing Capacity	'	'	$2,500,000,000	'	'	'	'	'
Line of Credit Facility, Current Borrowing Capacity	'	'	1,300,000,000	'	'	'	'	'
Borrowing Base, Line of Credit	'	'	2,200,000,000	'	'	'	'	2,400,000,000
Percentage of Proved Oil and Gas Properties Secured for Credit Facility Borrowing	'	'	75.00%	'	'	'	'	'
Line of Credit, Covenant Compliance, Maximum Annual Dividend Payment	'	'	50,000,000	'	'	'	'	'
Debt Instrument, Covenant Compliance, Dividends Excluded From Computation	'	'	'	6,500,000	'	'	'	'
6.625% Senior Notes, Due 2019	'	'	'	'	350,000,000	350,000,000	'	'
6.50% Senior Notes, Due 2021	'	'	'	'	350,000,000	350,000,000	'	'
6.50% Senior Notes, Due 2023	'	'	'	'	400,000,000	400,000,000	'	'
5% Senior Notes, Due 2024	'	'	'	'	500,000,000	500,000,000	500,000,000	'
Senior Notes	$1,600,000,000	$1,600,000,000	'	'	$1,600,000,000	$1,600,000,000	'	'

LongTerm_Debt_Credit_Facility_

Long-Term Debt Credit Facility Available Borrowing Capacity (Details) (USD $)	Sep. 30, 2014		Dec. 31, 2013		Oct. 22, 2014		Sep. 30, 2014	Oct. 06, 2014
					Subsequent Event [Member]		Line of Credit [Member]	Line of Credit [Member]
								Subsequent Event [Member]
Line of Credit Facility [Line Items]	'		'		'		'	'
Borrowing Base, Line of Credit	'		'		'		$2,200,000,000	$2,400,000,000
Line of Credit Facility, Amount Outstanding	390,000,000		0		558,500,000		'	'
Letters of Credit Outstanding, Amount	808,000	[1]	808,000	[1]	808,000	[1]	'	'
Line of Credit Facility, Remaining Borrowing Capacity	$909,192,000		$1,299,192,000		$740,692,000		'	'
[1]	(1) Letters of credit reduce the available borrowing capacity under the credit facility on a dollar-for-dollar basis.

Commitments_and_Contingencies_

Commitments and Contingencies Narrative (Details) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended		1 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014	Oct. 29, 2014	Oct. 27, 2014	Sep. 30, 2014	Oct. 15, 2014
						Drilling Rig Leasing Contracts [Member]	Subsequent Event [Member]	Subsequent Event [Member]	Gooseneck Prospect Acquisition [Member]	Gooseneck Prospect Acquisition [Member]
								Drilling Rig Leasing Contracts [Member]		Subsequent Event [Member]
Long-term Purchase Commitment [Line Items]	'	'	'	'	'	'	'	'	'	'
Potential Deficiency Payment	'	'	'	'	'	'	'	'	$24,400,000	$42,600,000
Commitments and Contingencies	'	'	'	'	'	'	'	'	'	'
Long-term Purchase Commitment, Amount	'	'	'	'	'	110,500,000	'	24,500,000	'	'
Purchase Commitment, Remaining Minimum Amount Committed	'	'	'	'	'	72,300,000	'	'	'	'
Liabilities Subject to Compromise, Early Contract Termination Fees	42,500,000	'	42,500,000	'	'	'	14,400,000	'	'	'
Gain (Loss) Related to Litigation Settlement	$1,579,000	$11,320,000	$31,509,000	$50,765,000	'	'	'	'	'	'

Commitments_and_Contingencies_1

Commitments and Contingencies Litigation Narrative (Details) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Jun. 30, 2014
					Endeavour Settlement [Member]
Litigation Estimate [Line Items]	'	'	'	'	'
Other operating revenues	$1,579	$11,320	$31,509	$50,765	$10,700

Compensation_Plans_Details

Compensation Plans (Details) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 23, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
RSUs, PSUs, and Director's Shares [Abstract]	'	'	'	'	'	'
Stock-based compensation expense	'	'	'	$24,568,000	$25,495,000	'
Stock option activity	'	'	'	'	'	'
Cash Retainer Maximum Deferral Percentage	'	'	'	100.00%	'	'
Cash Bonus Plan [Member]	'	'	'	'	'	'
Compensation plans	'	'	'	'	'	'
Cash Paid in Current Period for Bonus Compensation	'	'	'	41,700,000	16,000,000	'
Accrued Cash Bonus Plan Expense	'	6,200,000	5,800,000	19,000,000	16,700,000	'
Restricted Stock Units (RSUs) [Member]	'	'	'	'	'	'
Compensation plans	'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	'	$68.34	'	$68.34	'	$57.05
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	'	'	'	233,601	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	'	'	'	$84.11	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	'	'	'	-250,601	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	'	'	'	$58.09	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	'	'	'	-32,736	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	'	'	'	$59.07	'	'
RSUs, PSUs, and Director's Shares [Abstract]	'	'	'	'	'	'
Shares Paid for Tax Withholding for Share Based Compensation	80,766	'	'	'	'	'
Number of Common Shares to be Received Upon Settlement	'	'	'	1	'	'
Stock-based compensation expense	'	4,800,000	3,700,000	10,500,000	10,000,000	'
Unrecognized stock based compensation expense	'	26,700,000	'	26,700,000	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value	'	'	'	19,600,000	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	'	530,695	'	530,695	'	580,431
Stock option activity	'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period, Net of Shares Withheld for Tax	169,835	'	'	'	'	'
Performance Shares [Member]	'	'	'	'	'	'
Compensation plans	'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	'	$73.31	'	$73.31	'	$66.07
Multiplier Applied to PSU Awards at Settlement	'	'	'	0.55	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	'	'	'	202,404	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	'	'	'	$94.66	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	'	'	'	115,784	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	'	'	'	$59.30	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	'	'	'	129,491	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	'	'	'	$87.21	'	'
RSUs, PSUs, and Director's Shares [Abstract]	'	'	'	'	'	'
Shares Paid for Tax Withholding for Share Based Compensation	'	'	'	45,042	'	'
Stock-based compensation expense	'	4,800,000	3,500,000	11,600,000	13,200,000	'
Unrecognized stock based compensation expense	'	24,700,000	'	24,700,000	'	'
Share-based Compensation, Awards Other Than Options, Performance Measurement Period	'	'	'	3	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value	'	'	'	19,200,000	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	'	529,598	'	529,598	'	572,469
Stock option activity	'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period, Net of Shares Withheld for Tax	'	'	'	85,121	'	'
Performance Shares [Member] | Maximum [Member]	'	'	'	'	'	'
RSUs, PSUs, and Director's Shares [Abstract]	'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Low End of Range	'	'	'	200.00%	'	'
Performance Shares [Member] | Minimum [Member]	'	'	'	'	'	'
RSUs, PSUs, and Director's Shares [Abstract]	'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Low End of Range	'	'	'	0.00%	'	'
Employee Stock Option [Member]	'	'	'	'	'	'
Compensation plans	'	'	'	'	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price	'	$20.87	'	$20.87	'	$20.87
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	'	1,117,000	'	1,117,000	'	2,433,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Number	'	19,544	'	19,544	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Exercise Price	'	$20.87	'	$20.87	'	'
Vested at the end of the period	'	1,117,000	'	1,117,000	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	'	'	'	-19,544	'	'
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	'	'	'	$20.87	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	'	'	'	1,237,000	'	'
Stock option activity	'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	'	'	'	$0	'	'
Stock options outstanding at the beginning of the period (in shares)	'	'	'	39,088	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period	'	'	'	0	'	'
Stock options outstanding at the end of the period (in shares)	'	19,544	'	19,544	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Intrinsic Value	'	'	'	$0	'	'
Shares Issued to the Board of Directors [Member]	'	'	'	'	'	'
Compensation plans	'	'	'	'	'	'
Stock Issued During Period, Shares, Share-based Compensation, Gross	'	'	'	27,677	28,169	'
RSUs, PSUs, and Director's Shares [Abstract]	'	'	'	'	'	'
Stock-based compensation expense	'	196,000	0	1,400,000	1,400,000	'
Employee Stock [Member]	'	'	'	'	'	'
Compensation plans	'	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate	'	15.00%	'	15.00%	'	'
Stock Issued During Period, Shares, Employee Stock Purchase Plans	'	35,249	44,437	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription	'	25,000	'	25,000	'	'
ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentOfOfferingDatePricePaid	'	'	'	85.00%	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	'	1,200,000	'	1,200,000	'	'
Net Profits Plan [Member]	'	'	'	'	'	'
RSUs, PSUs, and Director's Shares [Abstract]	'	'	'	'	'	'
Cash Payments Made or Accrued under Profit Sharing Plan Related to Divested Property	'	$8,300,000	$2,600,000	$8,300,000	'	'

Compensation_Plans_Non_Stockba

Compensation Plans Non Stock-based Compensation (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Cash Bonus Plan [Member]	'	'	'	'
Cash Paid in Current Period for Bonus Compensation	'	'	$41,700,000	$16,000,000
Accrued Cash Bonus Plan Expense	6,200,000	5,800,000	19,000,000	16,700,000
Net Profits Plan [Member]	'	'	'	'
General and administrative expense	2,487,000	4,302,000	7,451,000	11,531,000
Exploration expense	162,000	329,000	644,000	1,026,000
Total	$2,649,000	$4,631,000	$8,095,000	$12,557,000

Compensation_Plans_Nonqualifie

Compensation Plans Non-qualified Deferred Compensation Plan (Details)	9 Months Ended
	Sep. 30, 2014
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'
Cash Retainer Minimum Deferral Percentage	0.00%
Non-qualified Deferred Compensation Plan [Member]	'
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]	'
Base Salary Minimum Deferral Percentage	0.00%
Base Salary Maximum Deferral Percentage	50.00%
Cash Bonus Minimum Deferral Percentage	0.00%
Cash Bonus Maximum Deferral Percentage	100.00%
Company Percentage Contribution of Employee Deferred Amount	100.00%
Company Percentage Contribution Limit of Employee Deferred Amount	6.00%
Employee Vesting Percentage in Company Contribution After Two Years	40.00%
Employee Vesting Percentage in Company Contribution Year Three and Each Year Thereafter	20.00%
Distribution Option Minimum Years	1
Distribution Option Maximum Years	10

Pension_Benefits_Details

Pension Benefits (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Components of Net Periodic Benefit Costs for Both Pension Plans	'	'	'	'
Service cost	$1,584,000	$1,572,000	$4,752,000	$4,718,000
Interest cost	548,000	407,000	1,643,000	1,220,000
Expected return on plan assets that reduces periodic pension costs	-494,000	-384,000	-1,483,000	-1,153,000
Amortization of prior service costs	4,000	4,000	13,000	13,000
Amortization of net actuarial loss	172,000	306,000	516,000	917,000
Net periodic benefit cost	1,814,000	1,905,000	5,441,000	5,715,000
Percentage in excess of the greater of the benefit obligation or the market-related value of assets, gain and losses amortized (as a percent)	10.00%	'	10.00%	'
Defined Benefit Plan, Contributions by Employer	'	'	$5,300,000	'

Earnings_per_Share_Details

Earnings per Share (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Calculation of basic and diluted earnings per share	'	'	'	'
Net income	$208,938	$70,690	$334,325	$163,939
Basic weighted-average common shares outstanding	67,379	66,943	67,169	66,486
Add: dilutive effect of stock options, unvested RSU's, and contingent PSU's	1,051	1,310	1,089	1,483
Diluted weighted-average common shares outstanding	68,430	68,253	68,258	67,969
Basic net income per common share	$3.10	$1.06	$4.98	$2.47
Diluted net income per common share	$3.05	$1.04	$4.90	$2.41
Performance Shares [Member]	'	'	'	'
Earnings per share	'	'	'	'
Performance period to receive awards (in years)	'	'	3	'
Maximum [Member] | Performance Shares [Member]	'	'	'	'
Earnings per share	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	'	'	200.00%	'
Minimum [Member] | Performance Shares [Member]	'	'	'	'
Earnings per share	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	'	'	0.00%	'

Derivative_Financial_Instrumen2

Derivative Financial Instruments (Details)	Sep. 30, 2014
	bbl
Crude oil	'
Derivative Financial Instruments	'
Portion of Future Oil and Gas Production Being Hedged	17,600,000
Natural Gas [Member]	'
Derivative Financial Instruments	'
Portion of Gas Production Being Hedged	164,100,000
Natural Gas Liquids	'
Derivative Financial Instruments	'
Portion of Future Oil and Gas Production Being Hedged	1,800,000
IF El Paso Permian [Member]	'
Derivative Financial Instruments	'
Index percent of natural gas fixed swaps	4.00%
Index percent of natural gas collars	4.00%
IF HSC [Member]	'
Derivative Financial Instruments	'
Index percent of natural gas fixed swaps	83.00%
Index percent of natural gas collars	80.00%
IF NGPL TXOK [Member]	'
Derivative Financial Instruments	'
Index percent of natural gas fixed swaps	2.00%
IF NNG Ventura [Member]	'
Derivative Financial Instruments	'
Index percent of natural gas fixed swaps	2.00%
Index percent of natural gas collars	8.00%
IF Enable East N/S [Member] [Member]	'
Derivative Financial Instruments	'
Index percent of natural gas fixed swaps	8.00%
Index percent of natural gas collars	8.00%
IF CIG [Member]	'
Derivative Financial Instruments	'
Index percent of natural gas fixed swaps	1.00%
OPIS Mont. Belvieu LDH Propane [Member]	'
Derivative Financial Instruments	'
Index percent of NGL fixed swaps	67.00%
OPIS Mont. Belvieu Non-LDH Natural Gasoline [Member]	'
Derivative Financial Instruments	'
Index percent of NGL fixed swaps	33.00%
Collar [Member] | Crude oil	'
Derivative Financial Instruments	'
Portion of Future Oil and Gas Production Being Hedged	4,289,000
Collar [Member] | Natural Gas [Member]	'
Derivative Financial Instruments	'
Portion of Gas Production Being Hedged	13,002,000
Swap | Crude oil	'
Derivative Financial Instruments	'
Portion of Future Oil and Gas Production Being Hedged	13,327,000
Swap | Natural Gas [Member]	'
Derivative Financial Instruments	'
Portion of Gas Production Being Hedged	151,059,000
Swap | Natural Gas Liquids	'
Derivative Financial Instruments	'
Portion of Future Oil and Gas Production Being Hedged	1,761,000
Fourth Quarter Current Year [Member] | Collar [Member] | Crude oil	'
Derivative Financial Instruments	'
Portion of Future Oil and Gas Production Being Hedged	923,000
Weighted-Average Floor Price	85
Weighted-Average Ceiling Price	102.63
Fourth Quarter Current Year [Member] | Swap | Crude oil	'
Derivative Financial Instruments	'
Weighted-Average Contract Price	96.01
Portion of Future Oil and Gas Production Being Hedged	2,016,000
Fourth Quarter Current Year [Member] | Swap | Natural Gas [Member]	'
Derivative Financial Instruments	'
Weighted-Average Contract Price	4.02
Portion of Gas Production Being Hedged	22,014,000
Fourth Quarter Current Year [Member] | Swap | Natural Gas Liquids	'
Derivative Financial Instruments	'
Weighted-Average Contract Price	61.69
Portion of Future Oil and Gas Production Being Hedged	980,000
2015 [Member] | Collar [Member] | Crude oil	'
Derivative Financial Instruments	'
Portion of Future Oil and Gas Production Being Hedged	3,366,000
Weighted-Average Floor Price	85
Weighted-Average Ceiling Price	94.25
2015 [Member] | Collar [Member] | Natural Gas [Member]	'
Derivative Financial Instruments	'
Weighted-Average Floor Price	3.98
Weighted-Average Ceiling Price	4.3
Portion of Gas Production Being Hedged	13,002,000
2015 [Member] | Swap | Crude oil	'
Derivative Financial Instruments	'
Weighted-Average Contract Price	91.14
Portion of Future Oil and Gas Production Being Hedged	5,741,000
2015 [Member] | Swap | Natural Gas [Member]	'
Derivative Financial Instruments	'
Weighted-Average Contract Price	4.04
Portion of Gas Production Being Hedged	57,943,000
2015 [Member] | Swap | Natural Gas Liquids	'
Derivative Financial Instruments	'
Weighted-Average Contract Price	55.42
Portion of Gas Production Being Hedged	781,000
2016 [Member] | Swap | Crude oil	'
Derivative Financial Instruments	'
Weighted-Average Contract Price	88.01
Portion of Future Oil and Gas Production Being Hedged	5,570,000
2016 [Member] | Swap | Natural Gas [Member]	'
Derivative Financial Instruments	'
Weighted-Average Contract Price	4.17
Portion of Gas Production Being Hedged	37,472,000
2017 [Member] | Swap | Natural Gas [Member]	'
Derivative Financial Instruments	'
Weighted-Average Contract Price	4.21
Portion of Gas Production Being Hedged	23,430,000
2018 [Member] | Swap | Natural Gas [Member]	'
Derivative Financial Instruments	'
Weighted-Average Contract Price	4.31
Portion of Gas Production Being Hedged	10,200,000

Derivative_Financial_Instrumen3

Derivative Financial Instruments Fair Value (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Fair value of derivative assets and liabilities	'	'
Price Risk Derivatives, at Fair Value, Net	$50,900,000	$21,500,000
Derivative asset current	41,295,000	21,559,000
Derivative asset noncurrent	22,510,000	30,951,000
Derivative liability current	4,649,000	26,380,000
Derivatives liability noncurrent	8,243,000	4,640,000
Derivatives not designated as hedging instruments	'	'
Fair value of derivative assets and liabilities	'	'
Derivative asset current	41,295,000	21,559,000
Derivative asset noncurrent	22,510,000	30,951,000
Derivative liability current	4,649,000	26,380,000
Derivatives liability noncurrent	8,243,000	4,640,000
Level 2 | Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member]	'	'
Fair value of derivative assets and liabilities	'	'
Derivative assets not designated as hedging instruments	63,805,000	52,510,000
Derivative liabilities not designated as hedging instruments	$12,892,000	$31,020,000

Derivative_Financial_Instrumen4

Derivative Financial Instruments Gains and Losses (Details) (USD $)	3 Months Ended				9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts	'		'		'		'
Derivative cash settlement (gain) loss	$274	[1]	$1,288	[1]	$62,894	[1]	($12,715)	[1]
Derivative (gain) loss	-190,661	[2]	39,933	[2]	33,470	[2]	-14,685	[2]
Crude oil	'		'		'		'
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts	'		'		'		'
Derivative cash settlement (gain) loss	517		13,538		27,435		13,786
Derivative (gain) loss	-141,429		30,488		-42,802		8,233
Natural Gas	'		'		'		'
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts	'		'		'		'
Derivative cash settlement (gain) loss	1,687		-11,019		28,563		-18,752
Derivative (gain) loss	-43,039		-2,264		17,700		-12,462
Natural Gas Liquids	'		'		'		'
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts	'		'		'		'
Derivative cash settlement (gain) loss	-1,930		-1,231		6,896		-7,749
Derivative (gain) loss	($6,467)		$10,421		($4,322)		$2,259
[1]	(1)B Total derivative cash settlement (gain) loss is reported in the derivative cash settlement gain (loss) line item on the condensed consolidated statements of cash flows within net cash provided by operating activities.
[2]	(2)B Total derivative (gain) loss is reported in the derivative (gain) loss line item on the condensed consolidated statements of cash flows within net cash provided by operating activities.

Derivative_Financial_Instrumen5

Derivative Financial Instruments Offsetting of Derivative Assets and Liabilities (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Offsetting of Derivative Assets and Liabilities [Abstract]	'	'
Derivative Asset, Fair Value, Gross Asset	$63,805	$52,510
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	-12,744	-30,652
Derivative Asset, Fair Value, Amount Offset Against Collateral	51,061	21,858
Derivative Liability, Fair Value, Gross Liability	-12,892	-31,020
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	12,744	30,652
Derivative Liability, Fair Value, Amount Offset Against Collateral	($148)	($368)

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Sep. 30, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified
Assets:	'		'
Derivatives	$63,805		$52,510
Proved oil and gas properties	6,789,927		5,637,462
Unproved oil and gas properties	536,100		271,100
Disposal Group, Including Discontinued Operation, Long Lived Assets, Current	19,900		'
Liabilities:	'		'
Derivatives	-12,892		-31,020
Line of Credit Facility, Amount Outstanding	390,000		0
Asset Retirement Obligations, Noncurrent	123,905		115,659
Asset Retirement Obligation, Legally Restricted Assets, Fair Value	452		3,033
Fair Value, Measurements, Nonrecurring [Member] | Level 1	'		'
Assets:	'		'
Proved oil and gas properties	0	[1]	0	[1]
Unproved oil and gas properties	0	[1]	0	[1]
Disposal Group, Including Discontinued Operation, Long Lived Assets, Current	0	[1]	0	[1]
Liabilities:	'		'
Asset Retirement Obligations, Noncurrent	0		'
Asset Retirement Obligation, Legally Restricted Assets, Fair Value	0		'
Fair Value, Measurements, Nonrecurring [Member] | Level 2	'		'
Assets:	'		'
Proved oil and gas properties	0	[1]	0	[1]
Unproved oil and gas properties	0	[1]	0	[1]
Disposal Group, Including Discontinued Operation, Long Lived Assets, Current	0	[1]	0	[1]
Liabilities:	'		'
Asset Retirement Obligations, Noncurrent	0		'
Asset Retirement Obligation, Legally Restricted Assets, Fair Value	0		'
Fair Value, Measurements, Nonrecurring [Member] | Level 3	'		'
Assets:	'		'
Proved oil and gas properties	9,443	[1]	62,178	[1]
Unproved oil and gas properties	43,252	[1]	3,280	[1]
Disposal Group, Including Discontinued Operation, Long Lived Assets, Current	17,952	[1]	650	[1]
Liabilities:	'		'
Asset Retirement Obligations, Noncurrent	923		'
Asset Retirement Obligation, Legally Restricted Assets, Fair Value	452		'
Fair Value, Measurements, Recurring [Member] | Level 1	'		'
Liabilities:	'		'
Net Profits Plan Liability	0	[2]	0	[2]
Fair Value, Measurements, Recurring [Member] | Level 2	'		'
Liabilities:	'		'
Net Profits Plan Liability	0	[2]	0	[2]
Fair Value, Measurements, Recurring [Member] | Level 3	'		'
Liabilities:	'		'
Net Profits Plan Liability	41,705	[2]	56,985	[2]
Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member] | Level 1	'		'
Assets:	'		'
Derivatives	0	[2]	0	[2]
Liabilities:	'		'
Derivatives	0	[2]	0	[2]
Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member] | Level 2	'		'
Assets:	'		'
Derivatives	63,805	[2]	52,510	[2]
Liabilities:	'		'
Derivatives	12,892	[2]	31,020	[2]
Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member] | Level 3	'		'
Assets:	'		'
Derivatives	0	[2]	0	[2]
Liabilities:	'		'
Derivatives	$0	[2]	$0	[2]
[1]	This represents a non-financial asset or liability that is measured at fair value on a nonrecurring basis.
[2]	This represents a financial asset or liability that is measured at fair value on a recurring basis.

Fair_Value_Measurements_Fair_V1

Fair Value Measurements Fair Value Measurement (Details 2) (USD $)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014		Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Dec. 31, 2013
		Net Profit Plan liability [Member]		6.625% Senior Notes Due 2019 [Member]	6.625% Senior Notes Due 2019 [Member]	6.50% Senior Notes Due 2021 [Member]	6.50% Senior Notes Due 2021 [Member]	6.50% Senior Notes Due 2023 [Member]	6.50% Senior Notes Due 2023 [Member]	5.0% Senior Notes Due 2024 [Member]	5.0% Senior Notes Due 2024 [Member]
Liabiliity measured at fair value using Level 3 inputs	'	'		'	'	'	'	'	'	'	'
Long-term Debt, Fair Value	'	'		$364,000,000	$374,290,000	$371,875,000	$373,625,000	$415,500,000	$422,000,000	$492,500,000	$475,315,000
Net Profits Plan	'	'		'	'	'	'	'	'	'	'
Discount Rate Used to Calculate Currently in Payout Liabilities	'	12.00%		'	'	'	'	'	'	'	'
Period Used for Price Assumptions of Strip Prices of Liabilities	'	1		'	'	'	'	'	'	'	'
Percent Change in Commodity Prices for Sensitivity Analysis	'	5.00%		'	'	'	'	'	'	'	'
Sensitivity Analysis Change in Liability, Due to Change in Commodity Prices	'	4,000,000		'	'	'	'	'	'	'	'
Percent Change in Discount Rate for Sensitivity Analysis	'	1.00%		'	'	'	'	'	'	'	'
Sensitivity Analysis Decrease in Liability Due to Change in Discount Rate	'	2,000,000		'	'	'	'	'	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]	'	'		'	'	'	'	'	'	'	'
Beginning balance	'	56,985,000		'	'	'	'	'	'	'	'
Net increase in liability	'	1,156,000	[1]	'	'	'	'	'	'	'	'
Net settlements	'	-16,436,000	[1],[2]	'	'	'	'	'	'	'	'
Transfers in (out) of Level 3	'	0		'	'	'	'	'	'	'	'
Ending balance	'	$41,705,000		'	'	'	'	'	'	'	'
Proved Oil and Gas Properties	'	'		'	'	'	'	'	'	'	'
Discount Rate Used for Fair Value of Oil and Gas Properties	12.00%	'		'	'	'	'	'	'	'	'
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast	5	5		'	'	'	'	'	'	'	'
[1]	Net changes in the Companybs Net Profits Plan liability are shown in the Change in Net Profits Plan liability line item of the accompanying statements of operations
[2]	Settlements represent cash payments made or accrued under the Net Profits Plan. The Company accrued or made cash payments under the Net Profits Plan of $8.3 million as a result of divestitures during the nine months ended SeptemberB 30, 2014