SM Energy (SM) 10-Q 28 Oct 15 2015 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information Document - shares	9 Months Ended
	Sep. 30, 2015	Oct. 21, 2015
Entity Information [Line Items]
Entity Registrant Name	SM Energy Co
Entity Central Index Key	893,538
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		67,974,771
Entity Current Reporting Status	Yes

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (in thousands, except share amounts) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Assets
Cash and cash equivalents	$ 197	$ 120
Accounts receivable	171,067	322,630
Derivative asset	347,299	402,668
Prepaid expenses and other	19,114	19,625
Total current assets	537,677	745,043
Proved Oil and Gas Properties	7,468,331	7,348,436
Less - accumulated depletion, depreciation, and amortization	(3,240,109)	(3,233,012)
Unproved Oil and Gas Properties	381,869	532,498
Wells in progress	452,436	503,734
Oil and gas properties held for sale net of accumulated depletion, depreciation and amortization of $74,894 and $22,482, respectively	29,173	17,891
Other property and equipment, net of accumulated depreciation of $43,197 and $37,079, respectively	359,339	334,356
Total property and equipment, net	5,451,039	5,503,903
Derivative asset	147,530	189,540
Other noncurrent assets	77,615	78,214
Total other noncurrent assets	225,145	267,754
Total Assets	6,213,861	6,516,700
Liabilities
Accounts payable and accrued expenses	361,734	640,684
Derivative liability	2,900	0
Deferred tax liability	120,563	142,976
Other current liabilities	0	1,000
Total current liabilities	485,197	784,660
Revolving credit facility	184,000	166,000
Senior Notes (note 5)	2,350,000	2,200,000
Asset retirement obligation	118,153	120,867
Net Profits Plan liability	13,962	27,136
Deferred income taxes	833,352	891,681
Derivative liability	2,019	70
Other noncurrent liabilities	40,341	39,631
Total noncurrent liabilities	$ 3,541,827	$ 3,445,385
Commitments and contingencies (note 6)
Stockholders' equity:
Common stock, $0.01 par value - authorized: 200,000,000 shares; issued and outstanding; 67,968,714 and 67,463,060, respectively	$ 680	$ 675
Additional paid-in-capital	298,438	283,295
Retained earnings	1,899,803	2,013,997
Accumulated other comprehensive loss	(12,084)	(11,312)
Total stockholders' equity	2,186,837	2,286,655
Total Liabilities and Stockholders' Equity	$ 6,213,861	$ 6,516,700

Balance Sheet Parenthetical (Pa

Balance Sheet Parenthetical (Parentheticals) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization	$ 3,240,109	$ 3,233,012
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	67,968,714	67,463,060
Common Stock, Shares, Outstanding	67,968,714	67,463,060
Assets Held-for-sale [Member]
Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization	$ 74,894	$ 22,482
Other Capitalized Property Plant and Equipment [Member]
Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization	$ 43,197	$ 37,079

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) (in thousands, except per share amounts) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Operating revenues:
Oil, gas, and NGL production revenue	$ 366,615	$ 617,207	$ 1,201,186	$ 1,894,977
Net gain (loss) on divestiture activity (note 3)	2,415	(5,432)	38,497	52
Other operating revenues	2,121	7,011	13,548	31,457
Total operating revenues and other income	371,151	618,786	1,253,231	1,926,486
Operating expenses:
Oil, gas, and NGL production expense	184,568	178,390	554,404	519,697
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	243,879	183,259	680,984	548,255
Exploration	19,679	34,556	82,627	80,161
Impairment of proved properties	55,990	0	124,430	0
Abandonment and impairment of unproved properties	6,600	15,522	24,046	18,487
General and administrative	37,782	41,696	124,026	114,862
Change in Net Profits Plan liability	(4,364)	(6,399)	(13,174)	(15,280)
Derivative (gain) loss	(212,253)	(190,661)	(285,491)	33,470
Other operating expenses	7,166	5,444	34,589	19,505
Total operating expenses	339,047	261,807	1,326,441	1,319,157
Income (loss) from operations	32,104	356,979	(73,210)	607,329
Non-operating income (expense):
Other, net	27	(672)	623	(2,493)
Interest expense	(33,157)	(22,621)	(96,583)	(70,851)
Loss on extinguishment of debt	0	0	(16,578)	0
Income (loss) before income taxes	(1,026)	333,686	(185,748)	533,985
Income tax (expense) benefit	4,140	(124,748)	78,296	(199,660)
Net income (loss)	$ 3,114	$ 208,938	$ (107,452)	$ 334,325
Basic weighted-average common shares outstanding	67,961	67,379	67,638	67,169
Diluted weighted-average common shares outstanding	68,119	68,430	67,638	68,258
Basic net income (loss) per common share	$ 0.05	$ 3.10	$ (1.59)	$ 4.98
Diluted net income (loss) per common share	0.05	3.05	(1.59)	4.90
Dividends per common share	$ 0.05	$ 0.05	$ 0.10	$ 0.10

CONDENSED CONSOLIDATED STATEME5

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 3,114	$ 208,938	$ (107,452)	$ 334,325
Pension liability adjustment	(20)	196	(772)	526
Total other comprehensive income (loss), net of tax	(20)	196	(772)	526
Total comprehensive income (loss)	$ 3,094	$ 209,134	$ (108,224)	$ 334,851

CONDENSED CONSOLIDATED STATEME6

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Statement of Cash Flows [Abstract]
Net income (loss)	$ (107,452)	$ 334,325
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Net gain on divestiture activity	(38,497)	(52)
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	680,984	548,255
Exploratory dry hole expense	22,860	22,844
Impairment of proved properties	124,430	0
Abandonment and impairment of unproved properties	24,046	18,487
Stock-based compensation expense	20,492	24,568
Change in Net Profits Plan liability	(13,174)	(15,280)
Derivative (gain) loss	(285,491)	33,470
Derivative cash settlements	397,307	(62,894)
Amortization of deferred financing costs	5,803	4,433
Non-cash loss on extinguishment of debt	4,123	0
Deferred income taxes	(80,388)	198,180
Plugging and abandonment	(5,540)	(6,193)
Other, net	3,670	(2,934)
Changes in current assets and liabilities:
Accounts receivable	105,336	6,476
Prepaid expenses and other	587	234
Accounts payable and accrued expenses	(74,247)	(28,797)
Net cash provided by operating activities	784,849	1,075,122
Cash flows from investing activities:
Net proceeds from the sale of oil and gas properties	335,103	41,868
Capital expenditures	(1,261,871)	(1,317,862)
Acquisition of proved and unproved oil and gas properties	(7,088)	(459,277)
Other, net	(990)	(714)
Net cash used in investing activities	(934,846)	(1,735,985)
Cash flows from financing activities:
Proceeds from credit facility	1,604,500	536,500
Repayment of credit facility	(1,586,500)	(146,500)
Net proceeds from Senior Notes	490,951	0
Repayment of Senior Notes	(350,000)	0
Proceeds from sale of common stock	3,157	2,898
Dividends paid	(3,373)	(3,353)
Net share settlement from issuance of stock awards	(8,502)	(10,576)
Other, net	(159)	(85)
Net cash provided by financing activities	150,074	378,884
Net change in cash and cash equivalents	77	(281,979)
Cash and cash equivalents at beginning of period	120	282,248
Cash and cash equivalents at end of period	197	269
Supplemental schedule of additional cash flow information and noncash investing and financing activities:
Cash paid for interest, net of capitalized interest	88,920	79,119
Net cash paid for income taxes	$ 492	$ 1,979

CONDENSED CONSOLIDATED STATEME7

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) (in thousands) (Parenthetical) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Supplemental Cash Flow Information [Abstract]
Dividends	$ 3.4	$ 3.4
Capital Expenditures Incurred but Not yet Paid	141.5	$ 404.8
Noncash or Part Noncash Acquisition, Net Nonmonetary Assets Acquired (Liabilities Assumed)	$ 6.2

The Company and Business

The Company and Business	9 Months Ended
	Sep. 30, 2015
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.

Basis of Presentation, Signific

Basis of Presentation, Significant Accounting Policies, and Recently Issued Accounting Standards	9 Months Ended
	Sep. 30, 2015
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. These financial statements do not include all information and notes required by GAAP for annual 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, 2014 (the “ 2014 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, 2015 , through the filing date of this report. Certain prior period amounts have been reclassified to conform to the current presentation on the accompanying condensed consolidated financial statements. 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 2014 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 2014 Form 10-K. Recently Issued Accounting Standards Effective January 1, 2015, the Company adopted, on a prospective basis, Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) No. 2015-01, “Income Statement – Extraordinary and Unusual Items.” This ASU simplifies income statement presentation by eliminating the concept of extraordinary items. There was no impact to the Company’s financial statements or disclosures from the adoption of this standard. In April 2015, the FASB issued new authoritative accounting guidance requiring debt issuance costs to be presented on the balance sheet as a direct deduction from the carrying value of the related debt liability. This guidance is to be applied using a retrospective method and is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2015. Early adoption is permitted. In August 2015, effective upon release, the FASB issued related new authoritative accounting guidance allowing for deferred financing costs associated with line-of-credit arrangements to continue to be presented as assets. The Company is currently evaluating the provisions of this guidance and assessing its impact on the Company’s financial statements and disclosures. In August 2015, the FASB issued new authoritative accounting guidance to defer the effective date of the new revenue recognition standard by one year. The new revenue recognition standard is now effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017. Early adoption is permitted but only for annual periods, and interim periods within those annual periods, beginning after December 15, 2016. The Company is currently evaluating the provisions of this guidance and assessing its impact on the Company’s financial statements and disclosures. Other than as disclosed above or in the 2014 Form 10-K, there are no other new accounting standards that would have a material effect on the Company’s financial statements and disclosures that have been issued but not yet adopted by the Company as of September 30, 2015 , and through the filing date of this report.

Acquisitions, Divestitures, and

Acquisitions, Divestitures, and Assets Held for Sale (Notes)	9 Months Ended
	Sep. 30, 2015
Divestiture Activity [Abstract]
Acquisitions, Divestitures, and Assets Held for Sale	Note 3 – Acquisitions, Divestitures, and Assets Held for Sale Divestitures During the second quarter of 2015, the Company divested its Mid-Continent assets in separate transactions for total cash proceeds received at closing, which reflect aggregate gross purchase price net of closing adjustments (referred to throughout this report as “divestiture proceeds”) of $316.5 million and an estimated total net gain of $108.4 million . These assets were classified as held for sale as of March 31, 2015, and certain of these assets were written down by $30.0 million during the three months ended March 31, 2015, to reflect fair value less estimated costs to sell. This write-down is reflected in the total net estimated gain of $108.4 million discussed above. These divestitures are subject to normal post-closing adjustments expected to occur in the fourth quarter of 2015 or early 2016. In conjunction with the Company’s efforts to divest its Mid-Continent assets, the Company previously announced the planned closure of its Tulsa, Oklahoma office in 2015, with the relocation of certain personnel to other Company offices. The Company expects to incur a total of approximately $10 million of exit and disposal costs associated with the severance, retention and relocation of employees, and other related matters, excluding the lease expenses discussed in the next paragraph. For the three and nine months ended September 30, 2015 , the Company recorded $1.0 million and $9.5 million , respectively, of exit and disposal costs, the majority of which were recorded as general and administrative expense in the accompanying condensed consolidated statements of operations (“accompanying statements of operations”). Additionally, during the third quarter of 2015, the Company vacated its office space in Tulsa. The Company has subleased a portion of the space and is currently attempting to sublease the remaining space. As of September 30, 2015 , the Company is obligated to pay lease costs of approximately $5.8 million , net of expected income from office space currently subleased, which will be expensed over the duration of the lease, which expires in 2022. This obligation will decrease if the Company successfully subleases additional space. 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. Any subsequent decreases to the estimated fair value less the costs to sell impact the measurement of assets held for sale. As of September 30, 2015 , the accompanying condensed consolidated balance sheets (“accompanying balance sheets”) present $29.2 million of assets held for sale, net of accumulated depletion, depreciation, and amortization expense, which primarily consist of certain non-core assets in the Company’s Permian region and certain assets in exploratory areas that the Company no longer intends to explore and develop in light of the low commodity price environment. There is a corresponding asset retirement obligation liability of approximately $3.3 million for assets held for sale recorded in the asset retirement obligation liability financial statement line item in the accompanying balance sheets. For the nine months ended September 30, 2015 , write-downs on certain assets held for sale totaled $98.6 million , which included the $30.0 million write-down recorded on certain Mid-Continent assets in the first quarter 2015 as discussed above. There were minimal adjustments on certain assets held for sale for the three months ended September 30, 2015. Write-downs on assets held for sale are recorded in the net gain (loss) on divestiture activity line item in the accompanying statements of operations. Subsequent to September 30, 2015, the Company entered into a purchase and sale agreement with a buyer for the sale of certain assets held for sale as of September 30, 2015 , in its Permian region. The Company expects to close this transaction in the fourth quarter of 2015 for a purchase price of approximately $26.0 million , subject to customary closing adjustments. The closing of this transaction is subject to the satisfaction of customary closing conditions, and there can be no assurance that the transaction will close on the expected closing date or at all. The Company determined that none of the planned nor executed asset sales qualify for discontinued operations accounting under financial statement presentation authoritative guidance.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Note 4 - Income Taxes Income tax expense (benefit) for the three and nine months ended September 30, 2015 , and 2014 , differs from the amount 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 or loss 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, 2015 2014 2015 2014 (in thousands) Current portion of income tax expense (benefit): Federal $ — $ — $ — $ — State (8,308 ) 479 2,092 1,480 Deferred portion of income tax expense (benefit) 4,168 124,269 (80,388 ) 198,180 Total income tax expense (benefit) $ (4,140 ) $ 124,748 $ (78,296 ) $ 199,660 403.5 % 37.4 % 42.2 % 37.4 % On a year-to-date basis, 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 cumulative effects of Texas and North Dakota enacted rate changes are reflected in the year-to-date deferred portion of income tax expense (benefit). During the nine months ended September 30, 2015, the Company determined certain Oklahoma properties sold in the quarter ended June 30, 2015, qualified for the Oklahoma capital gain deduction which resulted in additional state tax benefit. The Company is generally no longer subject to United States federal or state income tax examinations by tax authorities for years before 2007 . During the first quarter of 2015, as a result of its R&D credit settlement with the IRS Appeals Office in late 2014, the Company recorded an additional $2.0 million net R&D credit from a claim filed on an amended return. No R&D credit was recorded in 2014. During the quarter ended September 30, 2015, the IRS initiated an audit of the SM-Mitsui Tax Partnership for 2013. The Company has a significant investment in the underlying assets of the tax partnership.

Long-Term Debt

Long-Term Debt	9 Months Ended
	Sep. 30, 2015
Debt Disclosure [Abstract]
Long-term debt	Note 5 - Long-Term Debt Revolving Credit Facility The Company’s Fifth Amended and Restated Credit Agreement, as amended (the “Credit Agreement”), provides a maximum loan amount of $2.5 billion , current aggregate lender commitments of $1.5 billion , and a maturity date of December 10, 2019 . Effective as of October 7, 2015, the Company’s lenders decreased the borrowing base to $2.0 billion as part of the regularly scheduled semi-annual redetermination under the Credit Agreement. This expected reduction from $2.4 billion was primarily a result of the Company’s sale of its Mid-Continent assets completed in the second quarter of 2015, plus adjustments consistent with lower commodity prices. There was no change in the current aggregate lender commitments of $1.5 billion . The next redetermination date is scheduled for April 1, 2016 . Borrowings under the facility are secured by mortgages on assets having a value equal to at least 75 percent of the total value of the Company’s proved oil and gas properties. The Company must comply with certain financial and non-financial covenants under the terms of the Credit 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 Agreement as of September 30, 2015 , 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 Credit Agreement as of October 21, 2015 , September 30, 2015 , and December 31, 2014 : As of October 21, 2015 As of September 30, 2015 As of December 31, 2014 (in thousands) Credit facility balance $ 177,500 $ 184,000 $ 166,000 Letters of credit (1) $ 200 $ 200 $ 808 Available borrowing capacity $ 1,322,300 $ 1,315,800 $ 1,333,192 ____________________________________________ (1) Letters of credit reduce the amount available 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 notes shown in the table below (the “Senior Notes”): As of September 30, 2015 As of December 31, 2014 (in thousands) 6.625% Senior Notes due 2019 $ — $ 350,000 6.50% Senior Notes due 2021 350,000 350,000 6.125% Senior Notes due 2022 600,000 600,000 6.50% Senior Notes due 2023 400,000 400,000 5.0% Senior Notes due 2024 500,000 500,000 5.625% Senior Notes due 2025 500,000 — Total Senior Notes $ 2,350,000 $ 2,200,000 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 this restricted payment covenant. The Company was in compliance with all covenants under its Senior Notes as of September 30, 2015 , and through the filing date of this report. 2019 Notes On May 7, 2015, the Company commenced a cash tender offer for any and all of its outstanding 6.625% Senior Notes due 2019 (the “2019 Notes”) at a price of $1,036.88 per $1,000 of principal amount for all 2019 Notes tendered by May 20, 2015 (“Consent Payment Deadline”), and at a price of $1,006.88 per $1,000 of principal amount for all 2019 Notes properly tendered thereafter. On the Consent Payment Deadline, the Company received tenders and consents from the holders of approximately $242.9 million in aggregate principal amount, or approximately 69% , of its outstanding 2019 Notes in connection with the cash tender offer. Following its entry into the supplemental indenture dated as of May 21, 2015, to the indenture dated as of February 7, 2011, between the Company and U.S. Bank National Association, as Trustee, the Company accepted the 2019 Notes tendered as of the Consent Payment Deadline in exchange for payment of total consideration, including accrued interest, of approximately $256.2 million under the Tender Offer and Consent Solicitation. On June 5, 2015 , the Company accepted $1.5 million of 2019 Notes tendered after the Consent Payment Deadline in exchange for payment of total consideration, including accrued interest, of approximately $1.6 million . On June 22, 2015 , the Company redeemed the remaining outstanding 2019 Notes at a redemption price of 103.313% of the principal amount for payment of total consideration, including accrued interest, of approximately $111.5 million . The Company recorded a loss on extinguishment of debt related to the tender offer and redemption of its 2019 Notes of approximately $16.6 million for the quarter ended June 30, 2015 . This amount includes approximately $12.5 million associated with the premium paid for the tender offer and redemption of the 2019 Notes and approximately $4.1 million related to the acceleration of unamortized deferred financing costs. 2025 Notes On May 21, 2015 , the Company issued $500.0 million in aggregate principal amount of 5.625% Senior Notes due 2025 (the “2025 Notes”) to certain underwriters in a public offering registered under the Securities Act of 1933, as amended (the “Securities Act”). The 2025 Notes were issued at par and mature on June 1, 2025 . The Company received net proceeds of approximately $491.0 million after deducting fees of $9.0 million , which are being amortized as deferred financing costs over the life of the 2025 Notes. The net proceeds were used to fund the consideration paid to the tendering holders of the 2019 Notes and to redeem the remaining un-tendered 2019 Notes, as well as repay outstanding borrowings under the Credit Agreement and for general corporate purposes. Prior to June 1, 2018 , the Company may redeem, on one or more occasions, up to 35% of the aggregate principal amount of the 2025 Notes with the net cash proceeds of certain equity offerings at a redemption price of 105.625% of the principal amount thereof, plus accrued and unpaid interest. The Company may also redeem the 2025 Notes, in whole or in part, at any time after June 1, 2018, and prior to June 1, 2020 , at a redemption price equal to 100% of the principal amount of the 2025 Notes to be redeemed, plus a specified make-whole premium and accrued and unpaid interest to the applicable redemption date. On or after June 1, 2020 , the Company may also redeem all or, from time to time during the twelve-month period beginning on June 1 of each applicable year, a portion of the 2025 Notes at the redemption prices set forth below expressed as a percentage of the principal amount redeemed, plus accrued and unpaid interest: 2020 102.813 % 2021 101.875 % 2022 100.938 % 2023 and thereafter 100.000 % 2022 Notes The Company completed its offer to exchange its 6.125% Senior Notes due 2022 for notes registered under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), on July 10, 2015.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 6 - Commitments and Contingencies Commitments There were no material changes in commitments during the first nine months of 2015, except as further discussed below. Please refer to Note 6 - Commitments and Contingencies in the Company’s 2014 Form 10-K for additional discussion. In light of the low commodity price environment, the Company curtailed drilling activity during the first nine months of 2015. For the three and nine months ended September 30, 2015 , the Company incurred drilling rig termination fees of $2.2 million and $8.1 million , respectively, which are recorded in the other operating expenses line item in the accompanying statements of operations. During the third quarter of 2015, the Company entered into an amendment to a gas gathering agreement whereby the Company is subject to certain gathering throughput commitments for five years upon the expansion of the existing third party gathering system. The Company may be required to make periodic deficiency payments for any shortfalls in delivering the minimum annual volume commitment. In the event that no product is delivered in accordance with this agreement, the aggregate undiscounted deficiency payments beginning in 2017 and extending through 2022 would be approximately $142.7 million as of September 30, 2015 . As of the filing date of this report, the Company does not expect to incur any material shortfalls. 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 expected results of any 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. The Company is subject to routine severance, royalty and joint interest audits from regulatory authorities, non-operators and others, as the case may be, and records accruals for estimated exposure when a claim is deemed probable and estimable. Additionally, the Company is subject to various possible contingencies that arise from third party interpretations of the Company’s contracts or otherwise affecting the oil and natural gas industry. Such contingencies include differing interpretations as to the prices at which oil and natural gas sales may be made, the prices that royalty owners are paid for production from their leases, allowable costs under joint interest arrangements, and other matters. At September 30, 2015 , the Company had $4.6 million accrued for estimated exposure related to claims for payment of royalties on certain Federal and Indian leases. Although the Company believes that it has properly estimated its exposure with respect to the various contracts, laws and regulations, administrative rulings, and interpretations thereof, adjustments could be required as new interpretations and regulations arise.

Compensation Plans

Compensation Plans	9 Months Ended
	Sep. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Compensation Plans	Note 7 - Compensation Plans Performance Share Units Under the Equity Incentive Compensation Plan The Company grants performance share units (“PSUs”) to eligible employees as a part of its long-term 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 certain performance criteria 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 performance period and the relative performance of the Company’s TSR compared with the annualized TSR of certain peer companies for the performance period. Compensation expense for PSUs is recognized within general and administrative and exploration expense over the vesting periods of the respective awards. Total compensation expense recorded for PSUs for the three months ended September 30, 2015 , and 2014 , was $2.4 million and $4.8 million , respectively, and $7.4 million and $11.6 million for the nine months ended September 30, 2015 , and 2014 , respectively. As of September 30, 2015 , there was $21.3 million of total unrecognized compensation expense related to unvested PSU awards, which is being amortized through 2018 . A summary of the status and activity of non-vested PSUs for the nine months ended September 30, 2015 , is presented in the following table: PSUs (1) Weighted-Average Grant-Date Fair Value Non-vested at beginning of year 433,660 $ 73.63 Granted 320,753 $ 45.34 Vested (75,353 ) $ 51.59 Forfeited (47,787 ) $ 74.42 Non-vested at end of quarter 631,273 $ 61.83 ____________________________________________ (1) The number of awards assumes a multiplier of one . The final number of shares of common stock issued may vary depending on the three -year performance multiplier, which ranges from zero to two . During the first nine months of 2015 , the Company granted 320,753 PSUs with a fair value of $14.5 million as part of its regular annual long-term equity compensation program. These PSUs will fully vest on the third anniversary of the date of the grant. Also, during the first nine months of 2015 , the Company settled PSUs that were granted in 2012 , which earned a 1.0 times multiplier, by issuing 188,279 net shares of the Company’s common stock in accordance with the terms of the respective PSU awards. The Company and the majority of grant recipients mutually agreed to net share settle a portion of the awards to cover income and payroll tax withholdings in accordance with the Company’s Equity Incentive Compensation Plan and individual award agreements. As a result, 100,683 shares were withheld to satisfy income and payroll tax withholding obligations that arose upon delivery of the shares underlying the PSUs. Restricted Stock Units Under the Equity Incentive Compensation Plan The Company grants restricted stock units (“RSUs”) as part of its long-term equity compensation program. Each RSU represents a right to receive one share of the Company’s common stock upon settlement of the award at the end of the specified vesting period. Compensation expense for RSUs is recognized within general and administrative expense and exploration expense over the vesting periods of the award. Total compensation expense recorded for RSUs was $4.1 million and $4.8 million for the three months ended September 30, 2015 , and 2014 , respectively, and $9.9 million and $10.5 million for the nine months ended September 30, 2015 , and 2014 , respectively. As of September 30, 2015 , there was $22.7 million of total unrecognized compensation expense related to unvested RSU awards, which is being amortized through 2018 . A summary of the status and activity of non-vested RSUs for the nine months ended September 30, 2015 , is presented in the following table: RSUs Weighted-Average Grant-Date Fair Value Non-vested at beginning of year 515,724 $ 68.29 Granted 356,246 $ 43.72 Vested (267,244 ) $ 63.43 Forfeited (41,330 ) $ 68.63 Non-vested at end of quarter 563,396 $ 55.04 During the first nine months of 2015 , the Company granted 356,246 RSUs with a fair value of $15.6 million as part of its regular annual long-term equity compensation program. These RSUs will vest one-third of the total grant on each of the next three anniversaries of the date of the grant. Also, during the first nine months of 2015 , the Company settled 267,244 RSUs that related to awards granted in previous years. The Company and the majority of grant recipients mutually agreed to net share settle a portion of the awards to cover income and payroll tax withholdings in accordance with the Company’s Equity Incentive Compensation Plan and individual award agreements. As a result, the Company issued 181,187 net shares of common stock. The remaining 86,057 shares were withheld to satisfy income and payroll tax withholding obligations that arose upon delivery of the shares underlying those RSUs. Director Shares During the first nine months of 2015 and 2014 , the Company issued 37,950 and 27,677 shares, respectively, of its common stock to its non-employee directors, under the Company’s Equity Incentive Compensation Plan. The Company recorded approximately $271,000 and $196,000 of compensation expense related to these awards for the three months ended September 30, 2015 and 2014 , respectively. The Company recorded $1.4 million of compensation expense related to these awards for the nine months ended September 30, 2015 , and 2014 , 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 to the Company by the director, in which case that director’s shares vest upon the earlier of the completion of the one -year service period or the director retiring from the Board of Directors. 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% 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 Internal Revenue Code, as amended (“IRC”). The Company had approximately 1.1 million shares available for issuance under the ESPP as of September 30, 2015 . There were 96,285 and 35,249 shares issued under the ESPP during the nine months ended September 30, 2015 , and 2014 , respectively. The fair value of ESPP grants is measured at the date of grant using the Black-Scholes option-pricing model. Net Profits Plan Cash payments made or accrued under the Company’s Net Profits Plan totaled $410,000 and $2.6 million for the three months ended September 30, 2015 , and 2014 , respectively, and $3.6 million and $8.1 million for the nine months ended September 30, 2015 , and 2014 , respectively, the majority of which were recorded as general and administrative expense within the accompanying statements of operations. Additionally, the Company accrued or made cash payments under the Net Profits Plan of $3.8 million and $8.3 million for the nine months ended September 30, 2015 , and 2014 , respectively, as a result of the divestitures of properties subject to the Net Profits Plan. These cash payments are accounted for as a reduction in the net gain (loss) on divestiture activity line item in the accompanying statements of operations. The Company records changes in the present value of estimated future payments under the Net Profits Plan as a separate line item in the accompanying statements of operations. The change in the estimated liability is recorded as a non-cash expense or benefit in the current period. The amount recorded as an expense or benefit associated with the change in the estimated liability is not allocated to general and administrative expense or exploration expense because it is associated with the future net cash flows from oil and gas properties in the respective pools rather than results being realized through current period production. If the Company allocated the change in liability to these specific functional line items, based on the current allocation of actual distributions made by the Company, such expenses or benefits would predominately be allocated to general and administrative expense. As time has passed, the amount distributed relating to prospective exploration efforts has become insignificant as more is paid to employees that have terminated employment and do not provide ongoing exploration support to the Company.

Pension Benefits

Pension Benefits	9 Months Ended
	Sep. 30, 2015
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”). During the third quarter of 2015, the Company announced to its employees that it intends to freeze the Pension Plans to new participants, effective December 31, 2015. Employees currently participating in the Pension Plans will continue to earn benefits. 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, 2015 2014 2015 2014 (in thousands) Service cost $ 1,989 $ 1,584 $ 5,963 $ 4,752 Interest cost 624 548 1,872 1,643 Expected return on plan assets that reduces periodic pension costs (546 ) (494 ) (1,637 ) (1,483 ) Amortization of prior service costs 4 4 13 13 Amortization of net actuarial loss 371 172 1,114 516 Net periodic benefit cost $ 2,442 $ 1,814 $ 7,325 $ 5,441 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 $6.4 million to the Pension Plans during the nine months ended September 30, 2015 .

Earnings per Share

Earnings per Share	9 Months Ended
	Sep. 30, 2015
Earnings Per Share [Abstract]
Earnings per Share	Note 9 - Earnings Per Share Basic net income or loss per common share is calculated by dividing net income or loss 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 or loss per common share is calculated by dividing adjusted net income or loss by the diluted weighted-average common shares outstanding, which includes the effect of potentially dilutive securities. Potentially dilutive securities for this calculation consist of unvested RSUs, contingent PSUs, and in-the-money outstanding stock options. The treasury stock method is used to measure the dilutive impact of these stock awards. All remaining stock options were exercised during the year ended December 31, 2014, and therefore, were only dilutive for the three and nine months ended September 30, 2014 . 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 . When there is a loss from continuing operations, as was the case for the nine months ended September 30, 2015 , all potentially dilutive shares are anti-dilutive and are consequently excluded from the calculation of diluted net loss per common share. For the nine months ended September 30, 2015 , weighted-average anti-dilutive securities related to unvested RSUs and contingent PSUs totaled approximately 380,000 shares, respectively. 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, 2015 2014 2015 2014 (in thousands, except per share amounts) Net income (loss) $ 3,114 $ 208,938 $ (107,452 ) $ 334,325 Basic weighted-average common shares outstanding 67,961 67,379 67,638 67,169 Add: dilutive effect of stock options, unvested RSUs, and contingent PSUs 158 1,051 — 1,089 Diluted weighted-average common shares outstanding 68,119 68,430 67,638 68,258 Basic net income (loss) per common share $ 0.05 $ 3.10 $ (1.59 ) $ 4.98 Diluted net income (loss) per common share $ 0.05 $ 3.05 $ (1.59 ) $ 4.90

Derivative Financial Instrument

Derivative Financial Instruments	9 Months Ended
	Sep. 30, 2015
Derivative Instruments Not Designated as Hedging Instruments [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 collar arrangements for oil, gas, and NGLs. As of September 30, 2015 , the Company had commodity derivative contracts outstanding through the second quarter of 2020 for a total of 7.6 million Bbls of oil production, 190.4 million MMBtu of gas production, and 13.7 million Bbls of NGL production. Subsequent to September 30, 2015 , the Company entered into one derivative contract through the third quarter of 2016 for 886,000 Bbls of NGL production with a contract price of $20.16 per Bbl. This subsequent derivative contract for propane production is based on Oil Price Information Service (“OPIS”) Propane Mont Belvieu Non-TET. 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, 2015 : Oil Contracts Oil Swaps Contract Period NYMEX WTI Volumes Weighted-Average Contract Price (Bbls) (per Bbl) Fourth quarter 2015 1,137,000 $ 90.15 2016 5,570,000 $ 88.01 All oil swaps 6,707,000 Oil Collars Contract Period NYMEX WTI Volumes Weighted- Average Floor Price Weighted- Average Ceiling Price (Bbls) (per Bbl) (per Bbl) Fourth quarter 2015 869,000 $ 85.00 $ 92.19 All oil collars 869,000 Gas Contracts Gas Swaps Contract Period Volumes Weighted-Average Contract Price (MMBtu) (per MMBtu) Fourth quarter 2015 12,499,000 $ 4.01 2016 80,186,000 $ 3.61 2017 37,527,000 $ 4.09 2018 30,606,000 $ 4.27 2019 24,415,000 $ 4.34 All gas swaps* 185,233,000 *Gas swaps are comprised of IF El Paso Permian ( 2% ), IF HSC ( 95% ), IF NGPL TXOK ( 1% ), and IF NNG Ventura ( 2% ). Gas Collars Contract Period Volumes Weighted- Average Floor Price Weighted- Average Ceiling Price (MMBtu) (per MMBtu) (per MMBtu) Fourth quarter 2015 5,157,000 $ 3.99 $ 4.29 All gas collars* 5,157,000 *Gas collars are comprised of IF El Paso Permian ( 6% ), IF HSC ( 89% ), and IF NNG Ventura ( 5% ). NGL Contracts NGL Swaps OPIS Purity Ethane Mont Belvieu OPIS Propane Mont Belvieu Non-TET OPIS Normal Butane Mont Belvieu Non-TET OPS Isobutane Mont Belvieu Non-TET Contract Period Volumes Weighted-Average Contract Price Volumes Weighted-Average Volumes Weighted-Average Volumes Weighted-Average (Bbls) (per Bbl) (Bbls) (per Bbl) (Bbls) (per Bbl) (Bbls) (per Bbl) Fourth quarter 2015 — $ — 941,000 $ 19.60 322,000 $ 24.90 276,000 $ 25.30 2016 3,193,000 $ 8.47 2,746,000 $ 19.09 273,000 $ 25.62 233,000 $ 25.87 2017 2,271,000 $ 9.16 — $ — — $ — — $ — 2018 1,671,000 $ 10.65 — $ — — $ — — $ — 2019 1,200,000 $ 10.92 — $ — — $ — — $ — 2020 539,000 $ 11.13 — $ — — $ — — $ — Total NGL swaps 8,874,000 3,687,000 595,000 509,000 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 $489.9 million as of September 30, 2015 , and a net asset of $592.1 million as of December 31, 2014 . The following tables detail the fair value of derivatives recorded in the accompanying balance sheets, by category: As of September 30, 2015 Derivative Assets Derivative Liabilities Balance Sheet Classification Fair Value Balance Sheet Classification Fair Value (in thousands) Commodity contracts Current assets $ 347,299 Current liabilities $ 2,900 Commodity contracts Noncurrent assets 147,530 Noncurrent liabilities 2,019 Derivatives not designated as hedging instruments $ 494,829 $ 4,919 As of December 31, 2014 Derivative Assets Derivative Liabilities Balance Sheet Classification Fair Value Balance Sheet Classification Fair Value (in thousands) Commodity contracts Current assets $ 402,668 Current liabilities $ — Commodity contracts Noncurrent assets 189,540 Noncurrent liabilities 70 Derivatives not designated as hedging instruments $ 592,208 $ 70 Offsetting of Derivative Assets and Liabilities As of September 30, 2015 , and December 31, 2014 , all derivative instruments held by the Company were subject to 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 transactions that settle 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, 2015 December 31, 2014 September 30, 2015 December 31, 2014 (in thousands) Gross amounts presented in the accompanying balance sheets $ 494,829 $ 592,208 $ (4,919 ) $ (70 ) Amounts not offset in the accompanying balance sheets (4,919 ) (70 ) 4,919 70 Net amounts $ 489,910 $ 592,138 $ — $ — 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, 2015 2014 2015 2014 (in thousands) Derivative settlement (gain) loss: Oil contracts $ (90,493 ) $ 517 $ (270,622 ) $ 27,435 Gas contracts (1) (19,167 ) 1,687 (92,279 ) 28,563 NGL contracts (4,035 ) (1,930 ) (24,818 ) 6,896 Total derivative settlement (gain) loss (2) $ (113,695 ) $ 274 $ (387,719 ) $ 62,894 Total derivative (gain) loss: Oil contracts $ (131,728 ) $ (140,912 ) $ (138,839 ) $ (15,367 ) Gas contracts (66,538 ) (41,352 ) (142,807 ) 46,263 NGL contracts (13,987 ) (8,397 ) (3,845 ) 2,574 Total derivative (gain) loss (3) $ (212,253 ) $ (190,661 ) $ (285,491 ) $ 33,470 ____________________________________________ (1) Natural gas derivative settlements for the nine months ended September 30, 2015 , include a $15.3 million gain recorded in the second quarter of 2015 on the early settlement of futures contracts as a result of divesting of the Company’s Mid-Continent assets. (2) Total derivative settlement (gain) loss is reported net of the change in accrued settlements between periods in the derivative cash settlements line item on the condensed consolidated statements of cash flows within net cash provided by operating activities. (3) 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, 2015 , 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 mortgages on assets having a value equal to at least 75 percent of the total value of the Company’s proved oil and gas properties.

Fair Value Measurements Fair Va

Fair Value Measurements Fair Value Measurements	9 Months Ended
	Sep. 30, 2015
Fair Value Disclosures [Abstract]
Fair Value Disclosures [Text Block]	Note 11 - Fair Value Measurements The Company follows fair value measurement accounting guidance for all assets and liabilities measured at fair value. This 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 table is a listing of the Company’s assets and liabilities that are measured at fair value in the accompanying balance sheets and where they are classified within the fair value hierarchy as of September 30, 2015 : Level 1 Level 2 Level 3 (in thousands) Assets: Derivatives (1) $ — $ 494,829 $ — Proved oil and gas properties (2) $ — $ — $ 56,849 Oil and gas properties held for sale (2) $ — $ — $ 3,376 Liabilities: Derivatives (1) $ — $ 4,919 $ — Net Profits Plan (1) $ — $ — $ 13,962 ____________________________________________ (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 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 in the accompanying balance sheets and where they were classified within the hierarchy as of December 31, 2014 : Level 1 Level 2 Level 3 (in thousands) Assets: Derivatives (1) $ — $ 592,208 $ — Proved oil and gas properties (2) $ — $ — $ 33,423 Oil and gas properties held for sale (2) $ — $ — $ 17,891 Liabilities: Derivatives (1) $ — $ 70 $ — Net Profits Plan (1) $ — $ — $ 27,136 ____________________________________________ (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 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 forward commodity price curves, 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. The considered 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 derivative liability position. 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 valuation technique, 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 derivative 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, 2015 , would differ by approximately $1.5 million . A one percent increase or decrease in the discount rate would result in a change of approximately $500,000 . 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 of 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, 2015 (in thousands) Beginning balance $ 27,136 Net decrease in liability (1) (5,749 ) Net settlements (1) (2) (7,425 ) Transfers in (out) of Level 3 — Ending balance $ 13,962 ____________________________________________ (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 amount in the table includes cash payments made or accrued under the Net Profits Plan of $3.8 million for the nine months ended September 30, 2015 , as a result of the divestitures of properties subject to the Net Profits Plan. 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, 2015 , or December 31, 2014 , as they are recorded at historical value. As of September 30, 2015 As of December 31, 2014 (in thousands) 6.625% Senior Notes due 2019 $ — $ 350,018 6.50% Senior Notes due 2021 $ 336,658 $ 343,000 6.125% Senior Notes due 2022 $ 552,000 $ 556,500 6.50% Senior Notes due 2023 $ 374,000 $ 379,000 5.0% Senior Notes due 2024 $ 423,750 $ 435,000 5.625% Senior Notes due 2025 $ 430,000 $ — The carrying value of the Company’s credit facility approximates its fair value, as the applicable interest rates are floating, 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 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, 2015 , and December 31, 2014 . The Company believes 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 forecast 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 forecast 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. The Company recorded impairment of proved oil and gas properties expense of $56.0 million and $124.4 million for the three and nine months ended September 30, 2015 , respectively, due to continued declines in commodity strip prices since year-end 2014, the Company’s decision to reduce capital invested in the development of certain prospects in its South Texas & Gulf Coast and Permian regions, and a decline in performance of non-core assets. Proved properties measured at fair value within the accompanying balance sheets totaled $56.8 million as of September 30, 2015 . As of December 31, 2014, proved oil and gas properties measured at fair value totaled $33.4 million . 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. The Company recorded abandonment and impairment of unproved oil and gas properties expense of $6.6 million and $24.0 million for the three and nine months ended September 30, 2015 , respectively, related to acreage the Company no longer intended to develop. Unproved properties measured at fair value were written down to zero in the accompanying balance sheets as of September 30, 2015 , and December 31, 2014 . Proved properties classified as held for sale, including the corresponding asset retirement obligation liability, 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 available. If an estimated selling price is not available, the Company utilizes the income valuation technique discussed above. 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. For the nine months ended September 30, 2015 , write-downs on certain assets held for sale totaled $98.6 million . There were minimal adjustments on certain assets held for sale for the three months ended September 30, 2015 . These write-downs are included within the net gain (loss) on divestiture activity line item on the accompanying statements of operations. Please refer to Note 3 – Acquisitions, Divestitures, and Assets Held for Sale. 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.

Suspended Well Costs (Notes)

Suspended Well Costs (Notes)	9 Months Ended
	Sep. 30, 2015
Suspended Well Costs [Abstract]
Suspended Well Costs Disclosure [Text Block]	Note 12 - Suspended Well Costs For the nine months ended September 30, 2015 , the Company charged $21.1 million of exploratory well costs to exploration expense related to two unsuccessful exploratory wells that were capitalized as of December 31, 2014. None of the costs were capitalized for a period greater than one year as of December 31, 2014, or at the time the wells were determined to be unsuccessful.

Basis of Presentation, Signif20

Basis of Presentation, Significant Accounting Policies, and Recently Issued Accounting Standards (Policies)	9 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Fair Value of Financial Instruments, Policy [Policy Text Block]	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 forward commodity price curves, 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. The considered 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 derivative liability position. 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.

Fair Value Measurements Derivat

Fair Value Measurements Derivatives (Policies)	9 Months Ended
	Sep. 30, 2015
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments, Policy [Policy Text Block]	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 forward commodity price curves, 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. The considered 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 derivative liability position. 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.

Fair Value Measurements Net Pro

Fair Value Measurements Net Profits Plan (Policies)	9 Months Ended
	Sep. 30, 2015
Net Profits Plan [Abstract]
Net Profits Plan [Policy Text Block]	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 valuation technique, 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 derivative 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.

Fair Value Measurements Proved

Fair Value Measurements Proved & Unproved Oil and Gas Properties (Policies)	9 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Property, Plant and Equipment, Impairment [Policy Text Block]	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 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, 2015 , and December 31, 2014 . The Company believes 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 forecast 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 forecast 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. The Company recorded impairment of proved oil and gas properties expense of $56.0 million and $124.4 million for the three and nine months ended September 30, 2015 , respectively, due to continued declines in commodity strip prices since year-end 2014, the Company’s decision to reduce capital invested in the development of certain prospects in its South Texas & Gulf Coast and Permian regions, and a decline in performance of non-core assets. Proved properties measured at fair value within the accompanying balance sheets totaled $56.8 million as of September 30, 2015 . As of December 31, 2014, proved oil and gas properties measured at fair value totaled $33.4 million . 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. The Company recorded abandonment and impairment of unproved oil and gas properties expense of $6.6 million and $24.0 million for the three and nine months ended September 30, 2015 , respectively, related to acreage the Company no longer intended to develop. Unproved properties measured at fair value were written down to zero in the accompanying balance sheets as of September 30, 2015 , and December 31, 2014 . Proved properties classified as held for sale, including the corresponding asset retirement obligation liability, 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 available. If an estimated selling price is not available, the Company utilizes the income valuation technique discussed above. 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. For the nine months ended September 30, 2015 , write-downs on certain assets held for sale totaled $98.6 million . There were minimal adjustments on certain assets held for sale for the three months ended September 30, 2015 . These write-downs are included within the net gain (loss) on divestiture activity line item on the accompanying statements of operations. Please refer to Note 3 – Acquisitions, Divestitures, and Assets Held for Sale. 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.

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2015
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, 2015 2014 2015 2014 (in thousands) Current portion of income tax expense (benefit): Federal $ — $ — $ — $ — State (8,308 ) 479 2,092 1,480 Deferred portion of income tax expense (benefit) 4,168 124,269 (80,388 ) 198,180 Total income tax expense (benefit) $ (4,140 ) $ 124,748 $ (78,296 ) $ 199,660 403.5 % 37.4 % 42.2 % 37.4 %

Long-Term Debt (Tables)

Long-Term Debt (Tables)	9 Months Ended
	Sep. 30, 2015
Debt Disclosure [Abstract]
Schedule of Line of Credit Facilities [Table Text Block]	The following table presents the outstanding balance, total amount of letters of credit, and available borrowing capacity under the Credit Agreement as of October 21, 2015 , September 30, 2015 , and December 31, 2014 : As of October 21, 2015 As of September 30, 2015 As of December 31, 2014 (in thousands) Credit facility balance $ 177,500 $ 184,000 $ 166,000 Letters of credit (1) $ 200 $ 200 $ 808 Available borrowing capacity $ 1,322,300 $ 1,315,800 $ 1,333,192 ____________________________________________ (1) Letters of credit reduce the amount available under the credit facility on a dollar-for-dollar basis.
Schedule of Long-term Debt Instruments [Table Text Block]	The Senior Notes line on the accompanying balance sheets represents the outstanding principal amount of the notes shown in the table below (the “Senior Notes”): As of September 30, 2015 As of December 31, 2014 (in thousands) 6.625% Senior Notes due 2019 $ — $ 350,000 6.50% Senior Notes due 2021 350,000 350,000 6.125% Senior Notes due 2022 600,000 600,000 6.50% Senior Notes due 2023 400,000 400,000 5.0% Senior Notes due 2024 500,000 500,000 5.625% Senior Notes due 2025 500,000 — Total Senior Notes $ 2,350,000 $ 2,200,000
Debt Instrument Redemption [Table Text Block]	On or after June 1, 2020 , the Company may also redeem all or, from time to time during the twelve-month period beginning on June 1 of each applicable year, a portion of the 2025 Notes at the redemption prices set forth below expressed as a percentage of the principal amount redeemed, plus accrued and unpaid interest: 2020 102.813 % 2021 101.875 % 2022 100.938 % 2023 and thereafter 100.000 %

Compensation Plans Compensation

Compensation Plans Compensation Plans (Tables)	9 Months Ended
	Sep. 30, 2015
Compensation Related Costs [Abstract]
Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]	A summary of the status and activity of non-vested RSUs for the nine months ended September 30, 2015 , is presented in the following table: RSUs Weighted-Average Grant-Date Fair Value Non-vested at beginning of year 515,724 $ 68.29 Granted 356,246 $ 43.72 Vested (267,244 ) $ 63.43 Forfeited (41,330 ) $ 68.63 Non-vested at end of quarter 563,396 $ 55.04
Share-based Compensation, Performance Shares Award Unvested Activity [Table Text Block]	A summary of the status and activity of non-vested PSUs for the nine months ended September 30, 2015 , is presented in the following table: PSUs (1) Weighted-Average Grant-Date Fair Value Non-vested at beginning of year 433,660 $ 73.63 Granted 320,753 $ 45.34 Vested (75,353 ) $ 51.59 Forfeited (47,787 ) $ 74.42 Non-vested at end of quarter 631,273 $ 61.83 ____________________________________________ (1) The number of awards assumes a multiplier of one . The final number of shares of common stock issued may vary depending on the three -year performance multiplier, which ranges from zero to two .

Pension Benefits (Tables)

Pension Benefits (Tables)	9 Months Ended
	Sep. 30, 2015
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, 2015 2014 2015 2014 (in thousands) Service cost $ 1,989 $ 1,584 $ 5,963 $ 4,752 Interest cost 624 548 1,872 1,643 Expected return on plan assets that reduces periodic pension costs (546 ) (494 ) (1,637 ) (1,483 ) Amortization of prior service costs 4 4 13 13 Amortization of net actuarial loss 371 172 1,114 516 Net periodic benefit cost $ 2,442 $ 1,814 $ 7,325 $ 5,441

Earnings per Share (Tables)

Earnings per Share (Tables)	9 Months Ended
	Sep. 30, 2015
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, 2015 2014 2015 2014 (in thousands, except per share amounts) Net income (loss) $ 3,114 $ 208,938 $ (107,452 ) $ 334,325 Basic weighted-average common shares outstanding 67,961 67,379 67,638 67,169 Add: dilutive effect of stock options, unvested RSUs, and contingent PSUs 158 1,051 — 1,089 Diluted weighted-average common shares outstanding 68,119 68,430 67,638 68,258 Basic net income (loss) per common share $ 0.05 $ 3.10 $ (1.59 ) $ 4.98 Diluted net income (loss) per common share $ 0.05 $ 3.05 $ (1.59 ) $ 4.90

Derivative Financial Instrume29

Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2015
Derivative Instruments Not Designated as Hedging Instruments [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, 2015 : Oil Contracts Oil Swaps Contract Period NYMEX WTI Volumes Weighted-Average Contract Price (Bbls) (per Bbl) Fourth quarter 2015 1,137,000 $ 90.15 2016 5,570,000 $ 88.01 All oil swaps 6,707,000 Oil Collars Contract Period NYMEX WTI Volumes Weighted- Average Floor Price Weighted- Average Ceiling Price (Bbls) (per Bbl) (per Bbl) Fourth quarter 2015 869,000 $ 85.00 $ 92.19 All oil collars 869,000 Gas Contracts Gas Swaps Contract Period Volumes Weighted-Average Contract Price (MMBtu) (per MMBtu) Fourth quarter 2015 12,499,000 $ 4.01 2016 80,186,000 $ 3.61 2017 37,527,000 $ 4.09 2018 30,606,000 $ 4.27 2019 24,415,000 $ 4.34 All gas swaps* 185,233,000 *Gas swaps are comprised of IF El Paso Permian ( 2% ), IF HSC ( 95% ), IF NGPL TXOK ( 1% ), and IF NNG Ventura ( 2% ). Gas Collars Contract Period Volumes Weighted- Average Floor Price Weighted- Average Ceiling Price (MMBtu) (per MMBtu) (per MMBtu) Fourth quarter 2015 5,157,000 $ 3.99 $ 4.29 All gas collars* 5,157,000 *Gas collars are comprised of IF El Paso Permian ( 6% ), IF HSC ( 89% ), and IF NNG Ventura ( 5% ). NGL Contracts NGL Swaps OPIS Purity Ethane Mont Belvieu OPIS Propane Mont Belvieu Non-TET OPIS Normal Butane Mont Belvieu Non-TET OPS Isobutane Mont Belvieu Non-TET Contract Period Volumes Weighted-Average Contract Price Volumes Weighted-Average Volumes Weighted-Average Volumes Weighted-Average (Bbls) (per Bbl) (Bbls) (per Bbl) (Bbls) (per Bbl) (Bbls) (per Bbl) Fourth quarter 2015 — $ — 941,000 $ 19.60 322,000 $ 24.90 276,000 $ 25.30 2016 3,193,000 $ 8.47 2,746,000 $ 19.09 273,000 $ 25.62 233,000 $ 25.87 2017 2,271,000 $ 9.16 — $ — — $ — — $ — 2018 1,671,000 $ 10.65 — $ — — $ — — $ — 2019 1,200,000 $ 10.92 — $ — — $ — — $ — 2020 539,000 $ 11.13 — $ — — $ — — $ — Total NGL swaps 8,874,000 3,687,000 595,000 509,000
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, 2015 Derivative Assets Derivative Liabilities Balance Sheet Classification Fair Value Balance Sheet Classification Fair Value (in thousands) Commodity contracts Current assets $ 347,299 Current liabilities $ 2,900 Commodity contracts Noncurrent assets 147,530 Noncurrent liabilities 2,019 Derivatives not designated as hedging instruments $ 494,829 $ 4,919 As of December 31, 2014 Derivative Assets Derivative Liabilities Balance Sheet Classification Fair Value Balance Sheet Classification Fair Value (in thousands) Commodity contracts Current assets $ 402,668 Current liabilities $ — Commodity contracts Noncurrent assets 189,540 Noncurrent liabilities 70 Derivatives not designated as hedging instruments $ 592,208 $ 70
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, 2015 December 31, 2014 September 30, 2015 December 31, 2014 (in thousands) Gross amounts presented in the accompanying balance sheets $ 494,829 $ 592,208 $ (4,919 ) $ (70 ) Amounts not offset in the accompanying balance sheets (4,919 ) (70 ) 4,919 70 Net amounts $ 489,910 $ 592,138 $ — $ —
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, 2015 2014 2015 2014 (in thousands) Derivative settlement (gain) loss: Oil contracts $ (90,493 ) $ 517 $ (270,622 ) $ 27,435 Gas contracts (1) (19,167 ) 1,687 (92,279 ) 28,563 NGL contracts (4,035 ) (1,930 ) (24,818 ) 6,896 Total derivative settlement (gain) loss (2) $ (113,695 ) $ 274 $ (387,719 ) $ 62,894 Total derivative (gain) loss: Oil contracts $ (131,728 ) $ (140,912 ) $ (138,839 ) $ (15,367 ) Gas contracts (66,538 ) (41,352 ) (142,807 ) 46,263 NGL contracts (13,987 ) (8,397 ) (3,845 ) 2,574 Total derivative (gain) loss (3) $ (212,253 ) $ (190,661 ) $ (285,491 ) $ 33,470 ____________________________________________ (1) Natural gas derivative settlements for the nine months ended September 30, 2015 , include a $15.3 million gain recorded in the second quarter of 2015 on the early settlement of futures contracts as a result of divesting of the Company’s Mid-Continent assets. (2) Total derivative settlement (gain) loss is reported net of the change in accrued settlements between periods in the derivative cash settlements line item on the condensed consolidated statements of cash flows within net cash provided by operating activities. (3) 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 Fair 30

Fair Value Measurements Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Recurring and Nonrecurring [Table Text Block]	The following table is a listing of the Company’s assets and liabilities that are measured at fair value in the accompanying balance sheets and where they are classified within the fair value hierarchy as of September 30, 2015 : Level 1 Level 2 Level 3 (in thousands) Assets: Derivatives (1) $ — $ 494,829 $ — Proved oil and gas properties (2) $ — $ — $ 56,849 Oil and gas properties held for sale (2) $ — $ — $ 3,376 Liabilities: Derivatives (1) $ — $ 4,919 $ — Net Profits Plan (1) $ — $ — $ 13,962 ____________________________________________ (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 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 in the accompanying balance sheets and where they were classified within the hierarchy as of December 31, 2014 : Level 1 Level 2 Level 3 (in thousands) Assets: Derivatives (1) $ — $ 592,208 $ — Proved oil and gas properties (2) $ — $ — $ 33,423 Oil and gas properties held for sale (2) $ — $ — $ 17,891 Liabilities: Derivatives (1) $ — $ 70 $ — Net Profits Plan (1) $ — $ — $ 27,136 ____________________________________________ (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 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.
Net Profit Plan liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Profit Plan 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, 2015 (in thousands) Beginning balance $ 27,136 Net decrease in liability (1) (5,749 ) Net settlements (1) (2) (7,425 ) Transfers in (out) of Level 3 — Ending balance $ 13,962 ____________________________________________ (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 amount in the table includes cash payments made or accrued under the Net Profits Plan of $3.8 million for the nine months ended September 30, 2015 , as a result of the divestitures of properties subject to the Net Profits Plan.
Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes Fair Value [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, 2015 , or December 31, 2014 , as they are recorded at historical value. As of September 30, 2015 As of December 31, 2014 (in thousands) 6.625% Senior Notes due 2019 $ — $ 350,018 6.50% Senior Notes due 2021 $ 336,658 $ 343,000 6.125% Senior Notes due 2022 $ 552,000 $ 556,500 6.50% Senior Notes due 2023 $ 374,000 $ 379,000 5.0% Senior Notes due 2024 $ 423,750 $ 435,000 5.625% Senior Notes due 2025 $ 430,000 $ —

Acquisitions, Divestitures, a31

Acquisitions, Divestitures, and Assets Held for Sale Divestitures (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from sale of oil and gas properties			$ 335,103	$ 41,868
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down			98,600
Mid Continent Divestiture 2015 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from sale of oil and gas properties			316,500
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal			108,400
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down		$ 30,000
Business Exit Costs	$ 1,000		9,500
Mid Continent Divestiture 2015 [Member] | Mid Continent Lease Obligation net of Expected Income [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Mid Continent Lease Obligation net of Expected Income			$ 5,800
Scenario, Forecast [Member] | Mid Continent Divestiture 2015 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Exit Costs					$ 10,000

Acquisitions, Divestitures, a32

Acquisitions, Divestitures, and Assets Held for Sale Assets Held for Sale (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Oct. 21, 2015USD ($)	Dec. 31, 2014USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets Held-for-sale Reasonably Certain Period for Sale		1
Disposal Group, Including Discontinued Operation, Assets, Current		$ 29,173		$ 17,891
Asset Retirement Obligations Assets Held-for-sale Noncurrent		3,300
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down		$ 98,600
Mid Continent Divestiture 2015 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down	$ 30,000
Subsequent Event [Member] | Permian Divestiture 2015 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase Price for Divestiture Package			$ 26,000

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Components of the provision for income taxes
Federal	$ 0	$ 0	$ 0	$ 0
State	(8,308)	479	2,092	1,480
Deferred portion of income tax expense (benefit)	4,168	124,269	(80,388)	198,180
Total income tax expense (benefit)	$ (4,140)	$ 124,748	$ (78,296)	$ 199,660
Effective tax rate	403.50%	37.40%	42.20%	37.40%

Income Taxes Narrative (Details

Income Taxes Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2015USD ($)
Income Tax Narrative [Abstract]
Tax Credit Recorded for IRS R&D Settlement	$ 2

Long-Term Debt Revolving Credit

Long-Term Debt Revolving Credit Facility (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2015	Oct. 21, 2015	Jun. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term Line of Credit		$ 184,000			$ 166,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		2,500,000
Line of Credit Facility, Current Borrowing Capacity		1,500,000		$ 1,500,000
Borrowing Base, Line of Credit		$ 2,000,000		$ 2,400,000
Percentage of Proved Property Secured for Credit Facility Borrowing		75.00%
Line of Credit, Covenant Compliance, Maximum Annual Dividend Payment		$ 50,000
Long-term Line of Credit		184,000			166,000
Letters of Credit Outstanding, Amount	[1]	200			808
Line of Credit Facility, Remaining Borrowing Capacity		$ 1,315,800			$ 1,333,192
Subsequent Event [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Line of Credit			$ 177,500
Letters of Credit Outstanding, Amount	[1]		200
Line of Credit Facility, Remaining Borrowing Capacity			$ 1,322,300
[1]	Letters of credit reduce the amount available under the credit facility on a dollar-for-dollar basis.

Long-Term Debt Senior Notes (De

Long-Term Debt Senior Notes (Details) - USD ($)	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Jun. 22, 2015	Jun. 05, 2015	May. 21, 2015	May. 20, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Net proceeds from Senior Notes					$ 490,951,000	$ 0
Senior Notes	$ 2,350,000,000				2,350,000,000						$ 2,200,000,000
Loss on extinguishment of debt	0		$ 0		16,578,000	0
Gains (Losses) on Extinguishment of Debt, Non-Cash Portion					(4,123,000)	$ 0
Senior Notes [Member]
Debt Instrument [Line Items]
6.625% Senior Notes, Due 2019 Face Value	0				0						350,000,000
6.50% Senior Notes, Due 2021 Face Value	350,000,000				350,000,000						350,000,000
6.125% Senior Notes, Due 2022 Face Value	600,000,000				600,000,000						600,000,000
6.50% Senior Notes, Due 2023 Face Value	400,000,000				400,000,000						400,000,000
5% Senior Notes, Due 2024 Face Value	500,000,000				500,000,000						500,000,000
5.625% Senior Notes, Due 2025 Face Value	500,000,000				500,000,000						0
Senior Notes	$ 2,350,000,000				2,350,000,000						$ 2,200,000,000
Debt Instrument, Covenant Compliance, Dividends Excluded From Computation					$ 6,500,000
Senior Notes [Member] | 5.625% Senior Notes Due 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.625%				5.625%
Debt Instrument, Face Amount									$ 500,000,000
Debt Issuance Cost					$ 9,000,000
Senior Notes [Member] | 5.625% Senior Notes Due 2025 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage					105.625%
Debt Instrument, Maximum Early Redemption, Percentage of Principal					35.00%
Senior Notes [Member] | 5.625% Senior Notes Due 2025 [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage					100.00%
Senior Notes [Member] | 5.625% Senior Notes Due 2025 [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage					102.813%
Senior Notes [Member] | 5.625% Senior Notes Due 2025 [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage					101.875%
Senior Notes [Member] | 5.625% Senior Notes Due 2025 [Member] | Debt Instrument, Redemption, Period Five [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage					100.938%
Senior Notes [Member] | 5.625% Senior Notes Due 2025 [Member] | Debt Instrument, Redemption, Period Six [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage					100.00%
Senior Notes [Member] | 6.625% Senior Notes Due 2019 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.625%				6.625%
Price per Note Tendered								$ 1,006.88		$ 1,036.88
Debt Instrument, Face Amount, Individual Note								1,000		1,000
Debt Instrument, Repurchased Face Amount								1,500,000		$ 242,900,000
Percentage of Notes Tendered										69.00%
Debt Instrument, Repurchase Amount								$ 1,600,000		$ 256,200,000
Loss on extinguishment of debt		$ 16,578,000
Debt Instrument, Repurchase Premium		12,500,000
Gains (Losses) on Extinguishment of Debt, Non-Cash Portion		$ 4,123,000
Senior Notes [Member] | 6.625% Senior Notes Due 2019 [Member] | Early Debt Redemption, Year [Domain]
Debt Instrument [Line Items]
Debt Instrument, Repurchase Amount							$ 111,500,000
Debt Instrument, Redemption Price, Percentage				103.313%
Senior Notes [Member] | 6.50% Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.50%				6.50%
Senior Notes [Member] | 6.125% Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.125%				6.125%
Senior Notes [Member] | 6.50% Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.50%				6.50%
Senior Notes [Member] | 5% Senior Notes Due 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.00%				5.00%

Commitments and Contingencies C

Commitments and Contingencies Commitments and Contingencies (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015USD ($)	Sep. 30, 2015USD ($)
Drilling Rig Commitment [Domain]
Other Commitments [Line Items]
Gain (Loss) on Contract Termination	$ (2.2)	$ (8.1)
Through-put Commitment [Domain]
Other Commitments [Line Items]
Unrecorded Unconditional Purchase Obligation	$ 142.7	$ 142.7

Commitments and Contingencies L

Commitments and Contingencies Loss Contingency (Details) $ in Millions	Sep. 30, 2015USD ($)
Royalty Dispute [Domain]
Loss Contingencies [Line Items]
Loss Contingency Accrual	$ 4.6

Compensation Plans (Details)

Compensation Plans (Details)		3 Months Ended		9 Months Ended
		Sep. 30, 2015USD ($)$ / sharesshares	Sep. 30, 2014USD ($)	Sep. 30, 2015USD ($)$ / sharesshares	Sep. 30, 2014USD ($)shares	Dec. 31, 2014$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $				$ 20,492,000	$ 24,568,000
Share-based Compensation Arrangement by Share-based Payment Award, Assumed Number of Shares Awarded per Performance Stock Unit				1
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation, Awards Other Than Options, Performance Measurement Period		3		3
Stock-based compensation expense | $		$ 2,400,000	$ 4,800,000	$ 7,400,000	11,600,000
Unrecognized stock based compensation expense | $		$ 21,300,000		$ 21,300,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	[1]	631,273		631,273		433,660
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ / shares		$ 61.83		$ 61.83		$ 73.63
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	[1]			320,753
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares				$ 45.34
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	[1]			(75,353)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value | $ / shares				$ 51.59
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	[1]			(47,787)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value | $ / shares				$ 74.42
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value | $				$ 14,500,000
Multiplier Applied to PSU Awards Upon Settlement				1
Restricted Stock, Shares Issued Net of Shares for Tax Withholdings				188,279
Shares Paid for Tax Withholding for Share Based Compensation				100,683
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $		$ 4,100,000	4,800,000	$ 9,900,000	10,500,000
Unrecognized stock based compensation expense | $		$ 22,700,000		$ 22,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number		563,396		563,396		515,724
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ / shares		$ 55.04		$ 55.04		$ 68.29
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period				356,246
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares				$ 43.72
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period				(267,244)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value | $ / shares				$ 63.43
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period				(41,330)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value | $ / shares				$ 68.63
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value | $				$ 15,600,000
Restricted Stock, Shares Issued Net of Shares for Tax Withholdings				181,187
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted				267,244
Shares Paid for Tax Withholding for Share Based Compensation				86,057
Number of Shares Represented by Each RSU				1
Shares Issued to the Board of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $		$ 271,000	$ 196,000	$ 1,400,000	$ 1,400,000
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted				37,950	27,677
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				1 year
Shares Issued to the Board of Directors, Director with 5 or more years of service [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				5 years
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted				96,285	35,249
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate		15.00%		15.00%
Share-based Compensation Arragement by Share-based Payment Award, Maximum Employee Subscription | $		$ 25,000		$ 25,000
Share-based Compensation Arrangement by Share-Based Payment Award, Percent of Offering Date Price Paid				85.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		1,100,000		1,100,000
Minimum [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Awarded per Performance Stock Unit				0.00%
Maximum [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Awarded per Performance Stock Unit				200.00%
[1]	The number of awards assumes a multiplier of one. The final number of shares of common stock issued may vary depending on the three-year performance multiplier, which ranges from zero to two.

Compensation Plans Non Stock-ba

Compensation Plans Non Stock-based Compensation (Details) - Net Profits Plan [Member] - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Total Cash Payments, Made or Accrued under Profit Sharing Plan	$ 410,000	$ 2,600,000	$ 3,600,000	$ 8,100,000
Cash Payments Made or Accrued under Profit Sharing Plan Related to Divestiture Proceeds			$ 3,800,000	$ 8,300,000

Pension Benefits (Details)

Pension Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Components of Net Periodic Benefit Costs for Both Pension Plans
Service cost	$ 1,989	$ 1,584	$ 5,963	$ 4,752
Interest cost	624	548	1,872	1,643
Expected return on plan assets that reduces periodic pension costs	(546)	(494)	(1,637)	(1,483)
Amortization of prior service costs	4	4	13	13
Amortization of net actuarial loss	371	172	1,114	516
Net periodic benefit cost	$ 2,442	$ 1,814	$ 7,325	$ 5,441

Pension Benefits Pension Narrat

Pension Benefits Pension Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2015USD ($)
Pension Narrative [Abstract]
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%
Pension and Other Postretirement Benefit Contributions	$ 6.4

Earnings per Share (Details)

Earnings per Share (Details) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015USD ($)$ / sharesshares	Sep. 30, 2014USD ($)$ / sharesshares	Sep. 30, 2015USD ($)$ / sharesshares	Sep. 30, 2014USD ($)$ / sharesshares
Earnings per share
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			380,000
Calculation of basic and diluted earnings per share
Net income (loss) | $	$ 3,114	$ 208,938	$ (107,452)	$ 334,325
Basic weighted-average common shares outstanding	67,961,000	67,379,000	67,638,000	67,169,000
Add: dilutive effect of stock options, unvested RSU's, and contingent PSU's	158,000	1,051,000	0	1,089,000
Diluted weighted-average common shares outstanding	68,119,000	68,430,000	67,638,000	68,258,000
Basic net income (loss) per common share | $ / shares	$ 0.05	$ 3.10	$ (1.59)	$ 4.98
Diluted net income (loss) per common share | $ / shares	$ 0.05	$ 3.05	$ (1.59)	$ 4.90
Performance Shares [Member]
Earnings per share
Share-based Compensation, Awards Other Than Options, Performance Measurement Period	3		3
Minimum [Member] | Performance Shares [Member]
Earnings per share
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Awarded per Performance Stock Unit			0.00%
Maximum [Member] | Performance Shares [Member]
Earnings per share
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Awarded per Performance Stock Unit			200.00%

Derivative Financial Instrume44

Derivative Financial Instruments (Details)	Oct. 21, 2015$ / Barrelsbbl	Sep. 30, 2015MMBTU$ / EnergyContent$ / Barrelsbbl
Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		7,600,000
Natural Gas [Member]
Derivative Financial Instruments
Portion of Gas Production Being Hedged | MMBTU		190,400,000
Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		13,700,000
Swap | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		6,707,000
Swap | Natural Gas [Member]
Derivative Financial Instruments
Portion of Gas Production Being Hedged | MMBTU		185,233,000
Collar [Member] | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		869,000
Collar [Member] | Natural Gas [Member]
Derivative Financial Instruments
Portion of Gas Production Being Hedged | MMBTU		5,157,000
Fourth Quarter Current Year [Member] | Swap | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		1,137,000
Weighted-Average Contract Price | $ / Barrels		90.15
Fourth Quarter Current Year [Member] | Swap | Natural Gas [Member]
Derivative Financial Instruments
Weighted-Average Contract Price | $ / EnergyContent		4.01
Portion of Gas Production Being Hedged | MMBTU		12,499,000
Fourth Quarter Current Year [Member] | Collar [Member] | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		869,000
Weighted-Average Floor Price | $ / Barrels		85
Weighted-Average Ceiling Price | $ / Barrels		92.19
Fourth Quarter Current Year [Member] | Collar [Member] | Natural Gas [Member]
Derivative Financial Instruments
Portion of Gas Production Being Hedged | MMBTU		5,157,000
Weighted-Average Floor Price | $ / EnergyContent		3.99
Weighted-Average Ceiling Price | $ / EnergyContent		4.29
2016 [Member] | Swap | Crude oil
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		5,570,000
Weighted-Average Contract Price | $ / Barrels		88.01
2016 [Member] | Swap | Natural Gas [Member]
Derivative Financial Instruments
Weighted-Average Contract Price | $ / EnergyContent		3.61
Portion of Gas Production Being Hedged | MMBTU		80,186,000
2017 [Member] | Swap | Natural Gas [Member]
Derivative Financial Instruments
Weighted-Average Contract Price | $ / EnergyContent		4.09
Portion of Gas Production Being Hedged | MMBTU		37,527,000
2018 [Member] | Swap | Natural Gas [Member]
Derivative Financial Instruments
Weighted-Average Contract Price | $ / EnergyContent		4.27
Portion of Gas Production Being Hedged | MMBTU		30,606,000
2019 [Member] | Swap | Natural Gas [Member]
Derivative Financial Instruments
Weighted-Average Contract Price | $ / EnergyContent		4.34
Portion of Gas Production Being Hedged | MMBTU		24,415,000
IF NNG Ventura [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps		2.00%
Index percent of natural gas collars		5.00%
IF HSC [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps		95.00%
Index percent of natural gas collars		89.00%
IF NGPL TXOK [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps		1.00%
IF El Paso Permian [Member]
Derivative Financial Instruments
Index percent of natural gas fixed swaps		2.00%
Index percent of natural gas collars		6.00%
OPIS Normal Butane Mont Belvieu Non-TET [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		595,000
OPIS Normal Butane Mont Belvieu Non-TET [Member] | Fourth Quarter Current Year [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		322,000
Weighted-Average Contract Price | $ / Barrels		24.90
OPIS Normal Butane Mont Belvieu Non-TET [Member] | 2016 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		273,000
Weighted-Average Contract Price | $ / Barrels		25.62
OPIS Normal Butane Mont Belvieu Non-TET [Member] | 2017 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
OPIS Normal Butane Mont Belvieu Non-TET [Member] | 2018 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
OPIS Normal Butane Mont Belvieu Non-TET [Member] | 2019 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
OPIS Normal Butane Mont Belvieu Non-TET [Member] | 2020 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
OPIS Ethane Purity Mont Belvieu [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		8,874,000
OPIS Ethane Purity Mont Belvieu [Member] | Fourth Quarter Current Year [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
OPIS Ethane Purity Mont Belvieu [Member] | 2016 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		3,193,000
Weighted-Average Contract Price | $ / Barrels		8.47
OPIS Ethane Purity Mont Belvieu [Member] | 2017 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		2,271,000
Weighted-Average Contract Price | $ / Barrels		9.16
OPIS Ethane Purity Mont Belvieu [Member] | 2018 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		1,671,000
Weighted-Average Contract Price | $ / Barrels		10.65
OPIS Ethane Purity Mont Belvieu [Member] | 2019 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		1,200,000
Weighted-Average Contract Price | $ / Barrels		10.92
OPIS Ethane Purity Mont Belvieu [Member] | 2020 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		539,000
Weighted-Average Contract Price | $ / Barrels		11.13
OPIS Propane Mont Belvieu Non-TET [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		3,687,000
OPIS Propane Mont Belvieu Non-TET [Member] | Fourth Quarter Current Year [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		941,000
Weighted-Average Contract Price | $ / Barrels		19.60
OPIS Propane Mont Belvieu Non-TET [Member] | 2016 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		2,746,000
Weighted-Average Contract Price | $ / Barrels		19.09
OPIS Propane Mont Belvieu Non-TET [Member] | 2017 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
OPIS Propane Mont Belvieu Non-TET [Member] | 2018 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
OPIS Propane Mont Belvieu Non-TET [Member] | 2019 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
OPIS Propane Mont Belvieu Non-TET [Member] | 2020 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
OPIS Isobutane Mont Belvieu Non-TET [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		509,000
OPIS Isobutane Mont Belvieu Non-TET [Member] | Fourth Quarter Current Year [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		276,000
Weighted-Average Contract Price | $ / Barrels		25.30
OPIS Isobutane Mont Belvieu Non-TET [Member] | 2016 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		233,000
Weighted-Average Contract Price | $ / Barrels		25.87
OPIS Isobutane Mont Belvieu Non-TET [Member] | 2017 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
OPIS Isobutane Mont Belvieu Non-TET [Member] | 2018 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
OPIS Isobutane Mont Belvieu Non-TET [Member] | 2019 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
OPIS Isobutane Mont Belvieu Non-TET [Member] | 2020 [Member] | Swap | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged		0
Weighted-Average Contract Price | $ / Barrels		0
Subsequent Event [Member] | Natural Gas Liquids [Member]
Derivative Financial Instruments
Portion of Future Oil and Gas Production Being Hedged	886,000
Weighted-Average Contract Price | $ / Barrels	20.16
Revolving Credit Facility [Member]
Derivative Financial Instruments
Percentage of Proved Property Secured for Credit Facility Borrowing		75.00%

Derivative Financial Instrume45

Derivative Financial Instruments Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2015		Dec. 31, 2014
Fair value of derivative assets and liabilities
Price Risk Derivatives, at Fair Value, Net	$ 489,900		$ 592,100
Derivative asset current	347,299		402,668
Derivative asset noncurrent	147,530		189,540
Derivative Asset, Fair Value, Gross Asset	494,829		592,208
Derivative liability	2,900		0
Derivatives liability noncurrent	2,019		70
Derivative Liability, Fair Value, Gross Liability	4,919		70
Derivatives not designated as hedging instruments
Fair value of derivative assets and liabilities
Derivative asset current	347,299		402,668
Derivative asset noncurrent	147,530		189,540
Derivative liability	2,900		0
Derivatives liability noncurrent	2,019		70
Fair Value, Inputs, Level 2 [Member] | Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member]
Fair value of derivative assets and liabilities
Derivative Asset, Fair Value, Gross Asset	494,829	[1]	592,208	[2]
Derivative Liability, Fair Value, Gross Liability	$ 4,919	[1]	$ 70	[2]
[1]	This represents a financial asset or liability that is measured at fair value on a recurring basis.
[2]	This represents a financial asset or liability that is measured at fair value on a recurring basis.

Derivative Financial Instrume46

Derivative Financial Instruments Gains and Losses (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Total Derivative Settlement Gain (Loss)	[1]	$ 113,695	$ (274)	$ 387,719	$ (62,894)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	[2]	212,253	190,661	285,491	(33,470)
Crude oil
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Total Derivative Settlement Gain (Loss)		90,493	(517)	270,622	(27,435)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		131,728	140,912	138,839	15,367
Natural Gas
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Total Derivative Settlement Gain (Loss)	[3]	19,167	(1,687)	92,279	(28,563)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		66,538	41,352	142,807	(46,263)
Gain on Early Settlement of Derivatives				(15,300)
Natural Gas Liquids [Member]
Gain and loss from derivative cash settlements and changes in fair value of derivative contracts
Total Derivative Settlement Gain (Loss)		4,035	1,930	24,818	(6,896)
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		$ 13,987	$ 8,397	$ 3,845	$ (2,574)
[1]	Total derivative settlement (gain) loss is reported net of the change in accrued settlements between periods in the derivative cash settlements 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.
[3]	Natural gas derivative settlements for the nine months ended September 30, 2015, include a $15.3 million gain recorded in the second quarter of 2015 on the early settlement of futures contracts as a result of divesting of the Company’s Mid-Continent assets.

Derivative Financial Instrume47

Derivative Financial Instruments Offsetting of Derivative Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Offsetting of Derivative Assets and Liabilities [Abstract]
Derivative Asset, Fair Value, Gross Asset	$ 494,829	$ 592,208
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(4,919)	(70)
Derivative Asset, Fair Value, Amount Offset Against Collateral	489,910	592,138
Derivative Liability, Fair Value, Gross Liability	(4,919)	(70)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	4,919	70
Derivative Liability, Fair Value, Amount Offset Against Collateral	$ 0	$ 0

Fair Value Measurements Fair 48

Fair Value Measurements Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2015		Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 494,829		$ 592,208
Proved Oil and Gas Property, Successful Effort Method	7,468,331		7,348,436
Disposal Group, Including Discontinued Operation, Assets, Current	29,173		17,891
Derivative Liability, Fair Value, Gross Liability	4,919		70
Net Profits Plan liability	13,962		27,136
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Profits Plan liability	0	[1]	0	[2]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Profits Plan liability	0	[1]	0	[2]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Profits Plan liability	13,962	[1]	27,136	[2]
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proved Oil and Gas Property, Successful Effort Method	0	[3]	0	[4]
Disposal Group, Including Discontinued Operation, Assets, Current	0	[3]	0	[4]
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proved Oil and Gas Property, Successful Effort Method	0	[3]	0	[4]
Disposal Group, Including Discontinued Operation, Assets, Current	0	[3]	0	[4]
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proved Oil and Gas Property, Successful Effort Method	56,849	[3]	33,423	[4]
Disposal Group, Including Discontinued Operation, Assets, Current	3,376	[3]	17,891	[4]
Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	[1]	0	[2]
Derivative Liability, Fair Value, Gross Liability	0	[1]	0	[2]
Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset	494,829	[1]	592,208	[2]
Derivative Liability, Fair Value, Gross Liability	4,919	[1]	70	[2]
Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	[1]	0	[2]
Derivative Liability, Fair Value, Gross Liability	$ 0	[1]	$ 0	[2]
[1]	This represents a financial asset or liability that is measured at fair value on a recurring basis.
[2]	This represents a financial asset or liability that is measured at fair value on a recurring basis.
[3]	This represents a non-financial asset that is measured at fair value on a nonrecurring basis.
[4]	This represents a non-financial asset that is measured at fair value on a nonrecurring basis.

Fair Value Measurements Net P49

Fair Value Measurements Net Profits Plan (Details)		9 Months Ended
		Sep. 30, 2015USD ($)	Sep. 30, 2014USD ($)	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Profits Plan liability		$ 27,136,000
Net Profits Plan liability		13,962,000
Net Profit Plan liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Profits Plan liability		27,136,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease)	[1]	(5,749,000)
Net settlements (1) (2)	[1],[2]	(7,425,000)
Transfers in (out) of Level 3		0
Net Profits Plan liability		$ 13,962,000
Discount Rate Used to Calculate Currently in Payout Liabilities				12.00%
Number of Periods Used for Price Assumptions of Strip Prices		5
Period Used for Price Assumptions of Strip Prices for Liabilities		1
Percent Change in Commodity Prices for Sensitivity Analysis		5.00%
Sensitivity Analysis Change in Liability, Due to Change in Commodity Prices		$ 1,500,000
Percent Increase and Decrease in Discount Rate for Sensitivity Analysis		1.00%
Sensitivity Analysis Change in Liability Due to Change in Discount Rate		$ (500,000)
Net Profits Plan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Payments Made or Accrued under Profit Sharing Plan Related to Divestiture Proceeds		$ 3,800,000	$ 8,300,000
[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 amount in the table includes cash payments made or accrued under the Net Profits Plan of $3.8 million for the nine months ended September 30, 2015, as a result of the divestitures of properties subject to the Net Profits Plan

Fair Value Measurements Long-te

Fair Value Measurements Long-term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
6.625% Senior Notes Due 2019 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 0	$ 350,018
6.50% Senior Notes Due 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	336,658	343,000
6.125% Senior Notes Due 2022 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	552,000	556,500
6.50% Senior Notes Due 2023 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	374,000	379,000
5% Senior Notes Due 2024 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	423,750	435,000
5.625% Senior Notes Due 2025 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 430,000	$ 0
Senior Notes [Member] | 6.625% Senior Notes Due 2019 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.625%
Senior Notes [Member] | 6.50% Senior Notes Due 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.50%
Senior Notes [Member] | 6.125% Senior Notes Due 2022 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.125%
Senior Notes [Member] | 6.50% Senior Notes Due 2023 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.50%
Senior Notes [Member] | 5% Senior Notes Due 2024 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.00%
Senior Notes [Member] | 5.625% Senior Notes Due 2025 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.625%

Fair Value Measurements Prove51

Fair Value Measurements Proved and Unproved Oil and Gas Properties (Details)	3 Months Ended			9 Months Ended
	Sep. 30, 2015USD ($)A		Sep. 30, 2014USD ($)	Sep. 30, 2015USD ($)A		Sep. 30, 2014USD ($)	Dec. 31, 2014USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount Rate Used for Fair Value of Oil and Gas Properties	12.00%			12.00%
Impairment of Oil and Gas Properties	$ 55,990,000		$ 0	$ 124,430,000		$ 0
Proved Oil and Gas Property, Successful Effort Method	7,468,331,000			7,468,331,000			$ 7,348,436,000
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down				98,600,000
Abandonment and impairment of unproved properties	6,600,000		$ 15,522,000	24,046,000		$ 18,487,000
Unproved Oil and Gas Property, Successful Effort Method	381,869,000			381,869,000			532,498,000
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proved Oil and Gas Property, Successful Effort Method	56,849,000	[1]		56,849,000	[1]		33,423,000	[2]
Unproved Oil and Gas Property, Successful Effort Method	$ 0			$ 0			$ 0
Oil and Gas Properties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of Periods Used for Price Assumptions of Strip Prices | A	5			5
[1]	This represents a non-financial asset that is measured at fair value on a nonrecurring basis.
[2]	This represents a non-financial asset that is measured at fair value on a nonrecurring basis.

Suspended Well Costs (Details)

Suspended Well Costs (Details) $ in Millions	9 Months Ended
	Sep. 30, 2015USD ($)
Suspended Well Costs [Abstract]
Capitalized Exploratory Well Cost, Charged to Expense	$ (21.1)
Projects that have Exploratory Well Costs that have been Capitalized for Period Less than One Year, Number of Projects	2
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year	$ 0