Energen (EGN) 10-Q 9 May 17 2017 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	May 01, 2017
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q1
Entity Registrant Name	ENERGEN CORP
Entity Central Index Key	277,595
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding (shares)		97,188,418

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 88,658	$ 386,093
Accounts receivable, net	90,100	73,322
Inventories, net	15,365	14,222
Derivative instruments	7,594	50
Income tax receivable	26,246	27,153
Prepayments and other	5,024	5,071
Total current assets	232,987	505,911
Oil and natural gas properties, successful efforts method
Proved properties	7,767,171	7,543,464
Unproved properties	354,940	196,888
Less accumulated depreciation, depletion and amortization	(3,823,200)	(3,723,669)
Oil and natural gas properties, net	4,298,911	4,016,683
Other property and equipment, net	45,606	44,869
Total property, plant and equipment, net	4,344,517	4,061,552
Other postretirement assets	3,607	3,619
Noncurrent derivative instruments	9,293	0
Other assets	8,311	8,741
TOTAL ASSETS	4,598,715	4,579,823
Current Liabilities
Long-term debt due within one year	17,000	24,000
Accounts payable	79,644	65,031
Accrued taxes	10,153	7,252
Accrued wages and benefits	14,047	25,089
Accrued capital costs	120,825	79,988
Revenue and royalty payable	44,314	51,217
Derivative instruments	8,324	65,467
Other	14,368	20,160
Total current liabilities	308,675	338,204
Long-term debt	527,557	527,443
Asset retirement obligations	83,256	81,544
Deferred income taxes	516,295	495,888
Noncurrent derivative instruments	0	3,006
Other long-term liabilities	8,381	13,136
Total liabilities	1,444,164	1,459,221
Commitments and Contingencies
Shareholders’ Equity
Preferred stock, cumulative, $0.01 par value, 5,000,000 shares authorized	0	0
Common shareholders’ equity
Common stock, $0.01 par value; 150,000,000 shares authorized; 100,309,842 shares and 100,138,797 shares issued at March 31, 2017 and December 31, 2016, respectively	1,003	1,001
Premium on capital stock	1,376,517	1,372,569
Retained earnings	1,911,737	1,878,503
Accumulated other comprehensive income, net of tax
Postretirement plans	1,336	1,405
Deferred compensation plan	2,687	2,261
Treasury stock, at cost; 3,191,149 shares and 3,125,715 shares at March 31, 2017 and December 31, 2016, respectively	(138,729)	(135,137)
Total shareholders’ equity	3,154,551	3,120,602
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	$ 4,598,715	$ 4,579,823

Consolidated Balance Sheets (U3

Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2017	Dec. 31, 2016
Shareholders’ Equity
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	150,000,000	150,000,000
Common stock, shares issued (in shares)	100,309,842	100,138,797
Treasury stock, shares (in shares)	3,191,149	3,125,715

Consolidated Statements of Oper

Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenues
Oil, natural gas liquids and natural gas sales	$ 176,375	$ 122,764
Gain on derivative instruments, net	64,546	5,455
Total revenues	240,921	128,219
Operating Costs and Expenses
Oil, natural gas liquids and natural gas production	41,288	47,727
Production and ad valorem taxes	12,820	11,170
Depreciation, depletion and amortization	99,652	119,362
Asset impairment	1,460	220,025
Exploration	3,636	242
General and administrative (including non-cash stock based compensation of $3,197 and $2,471 for the three months ended March 31, 2017 and 2016, respectively)	20,399	29,525
Accretion of discount on asset retirement obligations	1,414	1,757
(Gain) loss on sale of assets and other	(1,175)	222
Total operating costs and expenses	179,494	430,030
Operating Income (Loss)	61,427	(301,811)
Other Income (Expense)
Interest expense	(8,966)	(9,833)
Other income	383	95
Total other expense	(8,583)	(9,738)
Income (Loss) Before Income Taxes	52,844	(311,549)
Income tax expense (benefit)	19,441	(108,433)
Net Income (Loss)	$ 33,403	$ (203,116)
Diluted Earnings Per Average Common Share (in dollars per share)	$ 0.34	$ (2.34)
Basic Earnings Per Average Common Share (in dollars per share)	$ 0.34	$ (2.34)
Diluted Average Common Shares Outstanding (in shares)	97,607	86,632
Basic Average Common Shares Outstanding (in shares)	97,140	86,632

Consolidated Statements of Ope5

Consolidated Statements of Operations (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Non-cash stock based compensation	$ 3,197	$ 2,471

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 33,403	$ (203,116)
Pension and postretirement plans:
Amortization of prior service cost, net of tax of ($43) and ($47), respectively	(71)	(78)
Amortization of net loss, including settlement charges, net of tax of $1 and $1,168, respectively	2	1,890
Current period change in fair value of pension and postretirement plans, net of tax of ($6) in 2016	0	(9)
Total pension and postretirement plans	(69)	1,803
Comprehensive Income (Loss)	$ 33,334	$ (201,313)

Consolidated Statements of Com7

Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Amortization of prior service cost, tax	$ (43)	$ (47)
Amortization of net loss including settlement charges, tax	1	1,168
Current period change in fair value of pension and postretirement plans, tax	$ 0	$ (6)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating Activities
Net income (loss)	$ 33,403	$ (203,116)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	99,652	119,362
Asset impairment	1,460	220,025
Accretion of discount on asset retirement obligations	1,414	1,757
Deferred income taxes	20,449	(107,149)
Change in derivative fair value	(71,686)	(5,151)
Loss on sale of assets	366	52
Stock-based compensation expense	3,197	2,471
Other, net	(3,696)	2,377
Net change in:
Accounts receivable	(16,778)	50,101
Inventories	(1,143)	(465)
Accounts payable	9,314	(17,192)
Accrued taxes/income tax receivable	3,808	2,179
Pension contributions	(29)	(14,516)
Other current assets and liabilities	(23,863)	(27,044)
Net cash provided by operating activities	55,868	23,691
Investing Activities
Additions to oil and natural gas properties	(183,714)	(137,296)
Acquisitions	(159,115)	(7,883)
Proceeds (payments) on the sale of assets, net	(308)	187
Net cash used in investing activities	(343,137)	(144,992)
Financing Activities
Issuance of common stock, net	0	381,219
Taxes paid for shares withheld	(3,166)	(2,419)
Reduction of long-term debt	(7,000)	0
Net change in credit facility	0	(222,500)
Tax benefit on stock compensation	0	(465)
Net cash provided by (used in) financing activities	(10,166)	155,835
Net change in cash and cash equivalents	(297,435)	34,534
Cash and cash equivalents at beginning of period	386,093	1,272
Cash and cash equivalents at end of period	$ 88,658	$ 35,806

Organization and Basis of Prese

Organization and Basis of Presentation	3 Months Ended
	Mar. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	ORGANIZATION AND BASIS OF PRESENTATION Energen Corporation (Energen or the Company) is an oil and natural gas exploration and production company engaged in the exploration, development and production of oil, natural gas liquids and natural gas. Our operations are conducted through our subsidiary, Energen Resources Corporation (Energen Resources) and primarily occur within the Midland Basin, the Delaware Basin and the Central Basin Platform areas of the Permian Basin in west Texas and New Mexico. Our corporate headquarters are located in Birmingham, Alabama. The unaudited consolidated financial statements and notes should be read in conjunction with the financial statements and notes thereto included in the 2016 Annual Report of Energen on Form 10-K. Our accompanying unaudited consolidated financial statements include Energen and its subsidiaries, principally Energen Resources, and have been prepared in accordance with accounting principles generally accepted in the United States of America for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the disclosures required for complete financial statements. Results of operations for interim periods are not necessarily indicative of the results that may be expected for the year. In the opinion of management, the accompanying financial statements reflect all adjustments necessary to present a fair statement of our financial position, results of operations, and cash flows for the periods and as of the dates shown. Such adjustments consist of normal recurring items. Certain reclassifications were made to conform prior periods’ financial statements to the current-quarter presentation. Workforce Reduction On January 22, 2016 and March 18, 2016, we reduced our workforce as part of an overall plan to reduce costs and better align our workforce with the needs of our business. In connection with the reductions, we incurred charges of approximately $5.0 million during 2016 for one-time termination benefits which are included in general and administrative expense on the consolidated statements of operations.

Derivative Commodity Instrument

Derivative Commodity Instruments	3 Months Ended
	Mar. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Commodity Instruments	DERIVATIVE COMMODITY INSTRUMENTS We periodically enter into derivative commodity instruments to hedge our exposure to price fluctuations on oil, natural gas liquids and natural gas production. These derivative commodity instruments are accounted for as mark-to-market transactions with gains or losses recognized in the period of change in gain (loss) on derivative instruments, net. Such instruments may include over-the-counter (OTC) swaps, options and basis swaps typically executed with investment and commercial banks and energy-trading firms. Derivative transactions are pursuant to standing authorizations by the Board of Directors, which do not authorize speculative positions. The following tables detail the offsetting of derivative assets and liabilities as well as the fair values of derivatives on the balance sheets: (in thousands) March 31, 2017 Gross Amounts Not Offset in the Balance Sheets Gross Amounts Recognized at Fair Value Gross Amounts Offset in the Balance Sheets Net Amounts Presented in the Balance Sheets Financial Instruments Cash Collateral Received Net Fair Value Presented in the Balance Sheets Derivatives not designated as hedging instruments Assets Derivative instruments $ 14,651 $ (7,057 ) $ 7,594 $ — $ — $ 7,594 Noncurrent derivative instruments 9,375 (82 ) 9,293 — — 9,293 Total derivative assets 24,026 (7,139 ) 16,887 — — 16,887 Liabilities Derivative instruments 15,381 (7,057 ) 8,324 — — 8,324 Noncurrent derivative instruments 82 (82 ) — — — — Total derivative liabilities 15,463 (7,139 ) 8,324 — — 8,324 Total derivatives $ 8,563 $ — $ 8,563 $ — $ — $ 8,563 (in thousands) December 31, 2016 Gross Amounts Not Offset in the Balance Sheets Gross Amounts Recognized at Fair Value Gross Amounts Offset in the Balance Sheets Net Amounts Presented in the Balance Sheets Financial Instruments Cash Collateral Received Net Fair Value Presented in the Balance Sheets Derivatives not designated as hedging instruments Assets Derivative instruments $ 1,756 $ (1,706 ) $ 50 $ — $ — $ 50 Liabilities Derivative instruments 67,173 (1,706 ) 65,467 — — 65,467 Noncurrent derivative instruments 3,006 — 3,006 — — 3,006 Total derivatives $ (68,423 ) $ — $ (68,423 ) $ — $ — $ (68,423 ) Due to the volatility of commodity prices, the estimated fair value of our derivative instruments is subject to fluctuation from period to period, which could result in significant differences between the current estimated fair value and the ultimate settlement price. Additionally, Energen is at risk of economic loss based upon the creditworthiness of our counterparties. We were in a net gain position with twelve of our active counterparties and in a net loss position with the remaining two at March 31, 2017 . The significant counterparty net gain positions at March 31, 2017 , J Aron and Company, J.P. Morgan Ventures Energy Corporation and Merrill Lynch Commodities, Inc., constituted approximately $2.4 million , $2.1 million and $1.9 million , respectively, of Energen’s total net gain on fair value of derivatives. The following table details the effect of open and closed derivative commodity instruments not designated as hedging instruments on the statements of operations: (in thousands) Location on Statements of Operations Three months Three months Gain recognized in income on derivatives Gain on derivative instruments, net $ 64,546 $ 5,455 As of March 31, 2017, Energen had entered into the following transactions for the remainder of 2017 and subsequent years: Production Period Description Total Hedged Volumes Average Contract Price Oil 2017 NYMEX Swaps 5,040 MBbl $50.13 Bbl NYMEX Three-Way Collars 3,600 MBbl Ceiling sold price (call) $62.18 Bbl Floor purchased price (put) $45.00 Bbl Floor sold price (put) $35.00 Bbl 2018 NYMEX Three-Way Collars 5,940 MBbl Ceiling sold price (call) $65.05 Bbl Floor purchased price (put) $50.00 Bbl Floor sold price (put) $40.00 Bbl Oil Basis Differential 2017 WTI/WTI Basis Swaps 7,560 MBbl $(0.64) Bbl 2018 WTI/WTI Basis Swaps 3,240 MBbl $(1.12) Bbl Natural Gas Liquids 2017 Liquids Swaps 62.4 MMGal $0.57 Gal 2018 Liquids Swaps 75.6 MMGal $0.60 Gal Natural Gas 2017 Basin Specific Swaps - Permian 11.4 Bcf $2.85 Mcf 2017 NYMEX Swaps 0.9 Bcf $3.29 Mcf Natural Gas Basis Differential 2017 Permian Swaps 0.9 Bcf $(0.29) Mcf WTI - West Texas Intermediate/Midland, WTI - West Texas Intermediate/Cushing Energen enters into three-way collars which are a combination of three options: a sold call, a purchased put and a sold put. The sold call establishes the maximum price that the Company will receive for the contracted commodity volumes. The purchased put establishes the minimum price that the Company will receive for the contracted volumes. The Company will receive the market price for the contracted volumes if the market price is between the sold call and the purchased put. If, however, the market price for the commodity falls below the sold put strike price, the minimum price that the Company will receive for the contracted volumes equals the market price plus the excess of the purchased put strike price over the sold put strike price. As of March 31, 2017 , the maximum term over which Energen has hedged exposures to the variability of cash flows is through December 31, 2018.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). In determining fair value, we use various valuation approaches and classify all assets and liabilities based on the lowest level of input that is significant to the fair value measurement. Observable inputs represent market data obtained from independent sources, whereas unobservable inputs reflect our own considerations about the assumptions other market participants would use in pricing the asset or liability based on the best information available in the circumstances. Assessing the significance of a particular input may require judgment considering factors specific to the asset or liability, and may affect the valuation of the asset or liability and its placement within the fair value hierarchy. The hierarchy is broken down into three levels based on the observability of inputs as follows: Level 1 - Unadjusted quoted prices in active markets for identical assets or liabilities; Level 2 - Pricing inputs other than quoted prices in active markets included within Level 1, which are either directly or indirectly observable through correlation with market data as of the reporting date; Level 3 - Pricing that requires inputs that are both significant and unobservable to the calculation of the fair value measure. The fair value measure represents estimates of the assumptions that market participants would use in pricing the asset or liability. Unobservable inputs are developed based on the best available information and subject to cost-benefit constraints. No transfers between fair value hierarchy levels occurred during the three months ended March 31, 2017 . Assets and Liabilities Measured at Fair Value on a Recurring Basis Energen classifies the fair value of multiple derivative instruments executed under master netting arrangements as net derivative assets and liabilities. The following fair value hierarchy tables present information about Energen’s assets and liabilities measured at fair value on a recurring basis: March 31, 2017 (in thousands) Level 2 Level 3 Total Assets: Derivative instruments $ 3,879 $ 3,715 $ 7,594 Noncurrent derivative instruments 7,434 1,859 9,293 Total assets 11,313 5,574 16,887 Liabilities: Derivative instruments (8,324 ) — (8,324 ) Net derivative asset $ 2,989 $ 5,574 $ 8,563 December 31, 2016 (in thousands) Level 2 Level 3 Total Assets: Derivative instruments $ 50 $ — $ 50 Liabilities: Derivative instruments (57,927 ) (7,540 ) (65,467 ) Noncurrent derivative instruments (1,694 ) (1,312 ) (3,006 ) Total liabilities (59,621 ) (8,852 ) (68,473 ) Net derivative liability $ (59,571 ) $ (8,852 ) $ (68,423 ) Derivative Instruments: The fair value of Energen’s derivative commodity instruments is determined using market transactions and other market evidence whenever possible, including market-based inputs to models and broker or dealer quotations. Our OTC derivative contracts trade in less liquid markets with limited pricing information as compared to markets with actively traded, unadjusted quoted prices; accordingly, the determination of fair value is inherently more difficult. OTC derivatives for which we are able to substantiate fair value through direct or indirect observable market prices are classified within Level 2 of the fair value hierarchy. These Level 2 fair values consist of swaps and options priced in reference to NYMEX oil and natural gas prices. OTC derivatives valued using unobservable market prices have been classified within Level 3 of the fair value hierarchy. These Level 3 fair values include oil basis and natural gas liquids swaps. We consider the frequency of pricing and variability in pricing between sources in determining whether a market is considered active. While Energen does not have access to the specific assumptions used in its counterparties’ valuation models, Energen maintains communications with its counterparties and discusses pricing practices. Further, we corroborate the fair value of our transactions by comparison of market-based price sources. Level 3 Fair Value Instruments: Energen prepared a sensitivity analysis to evaluate the hypothetical effect that changes in the prices used to estimate fair value would have on the fair value of its Level 3 instruments. We estimate that a 10 percent increase or decrease in commodity prices would result in an approximate $6.5 million change in the fair value of open Level 3 derivative contracts and to our results of operations. The table below sets forth a summary of changes in the fair value of Energen’s Level 3 derivative commodity instruments as follows: Three months ended March 31, (in thousands) 2017 2016 Balance at beginning of period $ (8,852 ) $ (16,059 ) Realized losses (3,253 ) (5,518 ) Unrealized gains relating to instruments held at the reporting date* 14,416 7,905 Settlements during period 3,263 5,518 Balance at end of period $ 5,574 $ (8,154 ) *Includes $10.9 million and $2.2 million in mark-to-market gains for the three months ended March 31, 2017 and 2016, respectively. The table below sets forth quantitative information about Energen’s Level 3 fair value measurements of derivative commodity instruments as follows: (in thousands, except price data) Fair Value as of March 31, 2017 Valuation Technique* Unobservable Input* Range Oil Basis - WTI/WTI 2017 $ 4,538 Discounted Cash Flow Forward Basis $(1.35 - $1.29) Bbl 2018 $ 806 Discounted Cash Flow Forward Basis ($1.40 - $1.35) Bbl Natural Gas Liquids 2017 $ (935 ) Discounted Cash Flow Forward Basis $0.59 Gal 2018 $ 1,165 Discounted Cash Flow Forward Basis $0.58 Gal *Discounted cash flow represents an income approach in calculating fair value including the referenced unobservable input and a discount reflecting credit quality of the counterparty. Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis Certain assets and liabilities are reported at fair value on a nonrecurring basis in Energen’s consolidated balance sheets. The following methods and assumptions were used to estimate the fair values. Asset retirement obligations: Energen’s asset retirement obligations (ARO) primarily relate to the future plugging, abandonment and reclamation of wells and facilities. We recognize a liability for the fair value of the ARO in the periods incurred. See Note 11, Asset Retirement Obligations, for further discussion related to these ARO’s. These assumptions are classified as Level 3 fair value measurements. Asset Impairments: We monitor our oil and natural gas properties as well as the market and business environments in which we operate and make assessments about events that could result in potential impairment. Such potential events may include, but are not limited to, commodity price declines, unanticipated increased operating costs, and lower than expected field production performance. If a material event occurs, Energen makes an estimate of undiscounted future cash flows to determine whether the asset is impaired. If the asset is impaired, we will record an impairment loss for the difference between the net book value of the properties and the fair value of the properties. The fair value of the properties typically is estimated using discounted cash flows and values derived from purchase and sale agreements and similar support as applicable. Cash flow and fair value estimates require Energen to make projections and assumptions for pricing, demand, competition, operating costs, legal and regulatory issues, discount rates and other factors for many years into the future. These assumptions are classified as Level 3 fair value measurements. See Note 13, Asset Impairment, for impairments recognized by Energen during the three months ended March 31, 2017 and 2016. Financial Instruments not Carried at Fair Value The stated value of cash and cash equivalents, short-term investments, accounts receivable (net of allowance), and short-term debt approximates fair value due to the short maturity of the instruments. The Company invested in certain short-term investments that qualify and were classified as cash and cash equivalents. Energen had allowance for doubtful accounts of $0.6 million at both March 31, 2017 and December 31, 2016, respectively. The fair value of Energen’s long-term debt, including the current portion, was approximately $548.5 million and $559.9 million and had a carrying value of $547.0 million and $554.0 million at March 31, 2017 and December 31, 2016 , respectively. The fair values are based on market prices of similar debt issues having the same remaining maturities, redemption terms and credit rating. Short-term debt is classified as a Level 1 fair value measurement and long-term debt is classified as a Level 2 fair value measurement.

Long-Term Debt

Long-Term Debt	3 Months Ended
	Mar. 31, 2017
Debt Disclosure [Abstract]
Long-Term Debt	LONG-TERM DEBT Long-term debt consisted of the following: (in thousands) March 31, 2017 December 31, 2016 7.40% Medium-term Notes, Series A, due July 24, 2017 $ — $ 2,000 7.36% Medium-term Notes, Series A, due July 24, 2017 15,000 15,000 7.23% Medium-term Notes, Series A, due July 28, 2017 2,000 2,000 7.32% Medium-term Notes, Series A, due July 28, 2022 20,000 20,000 7.60% Medium-term Notes, Series A, due July 26, 2027 — 5,000 7.35% Medium-term Notes, Series A, due July 28, 2027 10,000 10,000 7.125% Medium-term Notes, Series B, due February 15, 2028 100,000 100,000 4.625% Notes, due September 1, 2021 400,000 400,000 Total 547,000 554,000 Less amounts due within one year 17,000 24,000 Less unamortized debt discount 381 387 Less unamortized debt issuance costs 2,062 2,170 Total $ 527,557 $ 527,443 The aggregate maturities of Energen’s long-term debt outstanding at March 31, 2017 are as follows: (in thousands) Remaining 2017 2018 2019 2020 2021 2022 and thereafter $17,000 $— $— $— $400,000 $130,000 On January 23, 2017, Energen redeemed the $2.0 million of 7.40% Medium-term Notes, Series A, due July 24, 2017 and $5.0 million of 7.60% Medium-term Notes, Series A, due July 26, 2027. The debt agreements of Energen contain financial and nonfinancial covenants including routine matters such as timely payment of principal and interest, maintenance of corporate existence and restrictions on liens. Although none of the agreements have events of default based on credit ratings, the interest rates applicable to the syndicated credit facility discussed below may adjust based on credit rating changes during certain periods. Under Energen’s Indenture dated September 1, 1996 with The Bank of New York as Trustee, a cross default provision provides that any debt default of more than $10 million by Energen or Energen Resources will constitute an event of default by Energen. The Indenture does not include a restriction on the payment of dividends. Credit Facility: On September 2, 2014, Energen entered into a five -year syndicated secured credit facility with domestic and foreign lenders. On October 25, 2016, the borrowing and aggregate commitments base was reaffirmed at $1.05 billion with no changes in association with the semi-annual redetermination required under the agreement. On April 21, 2017, the borrowing base was increased to $1.4 billion . The aggregate commitment under the credit facility did not change and remains at $1.05 billion . Energen’s obligations under the syndicated credit facility are unconditionally guaranteed by Energen Resources. Subject to release of collateral in certain periods upon the achievement of certain investment grade ratings from designated ratings agencies, the credit facility is collateralized by certain assets of Energen, including a pledge of equity interests in subsidiaries of Energen other than Energen Resources, and by mortgages on substantially all of Energen Resources’ oil and natural gas properties. The current credit facility qualifies for classification as long-term debt on the consolidated balance sheets. The financial covenants of the credit facility require Energen to maintain a ratio of total debt to consolidated income before interest expense, income taxes, depreciation, depletion, amortization, exploration expense and other non-cash income and expenses (EBITDAX) less than or equal to 4.0 to 1.0; to maintain a ratio of consolidated current assets (adjusted to include amounts available for borrowings and exclude non-cash derivative instruments) to consolidated current liabilities (adjusted to exclude maturities under the credit facility and non-cash derivative instruments) greater than or equal to 1.0 to 1.0; and, during certain periods, to maintain a ratio of the net present value of proved reserves of our oil and natural gas properties to consolidated total debt greater than or equal to 1.50 to 1.0. We are also bound by covenants which limit our ability to incur additional indebtedness, make certain distributions or alter our corporate structure. Energen may not pay dividends during an event of default if the payment would result in an event of default or if availability is less than 10 percent of the loan limit under the credit facility. Our credit facility also limits our ability to enter into commodity hedges based on projected production volumes. In addition, the terms of our credit facility limit the amount we can borrow to a borrowing base amount which is determined by our lenders in their sole discretion based on their valuation of our proved reserves and their internal criteria including commodity price outlook. The borrowing base amount is subject to redetermination semi-annually and for event-driven unscheduled redeterminations. Our next scheduled redetermination is October 1, 2017. Under the credit facility, a cross default provision provides that any debt default of more than $75 million by Energen or Energen Resources will constitute an event of default by Energen. Upon an uncured event of default under the credit facility, all amounts owing under the credit facility, if any, depending on the nature of the event of default will automatically, or may upon notice by the administrative agent or the requisite lenders thereunder, become immediately due and payable and the lenders may terminate their commitments under the defaulted facility. Energen was in compliance with the terms of its credit facility as of March 31, 2017 . The following is a summary of information relating to Energen’s credit facility: (in thousands) March 31, 2017 December 31, 2016 Credit facility outstanding $ — $ — Available for borrowings 1,050,000 1,050,000 Total borrowing commitments $ 1,050,000 $ 1,050,000 Three months ended 2017 2016 Maximum amount outstanding at any month-end $ — $ 214,500 Average daily amount outstanding $ 28 $ 134,934 Weighted average interest rates based on: Average daily amount outstanding 2.05 % 1.72 % Amount outstanding at period-end — % — % Energen’s interest expense was $9.0 million and $9.8 million for the three months ended March 31, 2017 and 2016, respectively. For both the three months ended March 31, 2017 and 2016, Energen’s total interest expense included amortization of debt issuance costs related to long-term debt, including our credit facility, of $0.8 million . Energen had no capitalized interest for the three months ended March 31, 2017 and 2016. At March 31, 2017, Energen paid commitment fees on the unused portion of the available credit facility at a current annual rate of 30 basis points. Energen paid commitment fees of $0.8 million and $1.0 million for the three months ended March 31, 2017 and 2016, respectively.

Reconciliation of Earnings Per

Reconciliation of Earnings Per Share (EPS)	3 Months Ended
	Mar. 31, 2017
Earnings Per Share [Abstract]
Reconciliation of Earnings Per Share (EPS)	RECONCILIATION OF EARNINGS PER SHARE (EPS) Three months ended Three months ended (in thousands, except per share amounts) March 31, 2017 March 31, 2016 Net Per Share Net Per Share Income Shares Amount Loss Shares Amount Basic EPS $ 33,403 97,140 $ 0.34 $ (203,116 ) 86,632 $ (2.34 ) Effect of dilutive securities Stock options 31 — Non-vested restricted stock 262 — Performance share awards 174 — Diluted EPS $ 33,403 97,607 $ 0.34 $ (203,116 ) 86,632 $ (2.34 ) In periods of loss, shares that otherwise would have been included in diluted average common shares outstanding are excluded. The Company had 233,547 of excluded shares for the three months ended March 31, 2016. Energen had the following shares that were excluded from the computation of diluted EPS, as inclusion would be anti-dilutive: Three months ended (in thousands) 2017 2016 Stock options 267 — Performance share awards 131 —

Equity Offering

Equity Offering	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
Equity Offering	EQUITY OFFERING During the first quarter of 2016, Energen issued 18,170,000 additional shares of common stock through a public equity offering. We received net proceeds of approximately $381.1 million , after deducting offering expenses. Net proceeds from this offering were used to repay borrowings under our credit facility and for general corporate purposes.

Stock Compensation

Stock Compensation	3 Months Ended
	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Compensation	STOCK COMPENSATION Stock Incentive Plan Restricted Stock: The Stock Incentive Plan provides for the grant of restricted stock and restricted stock units (restricted stock awards) which have been valued based on the quoted market price of Energen’s common stock at the date of grant. Restricted stock awards vest within three years from grant date. A summary of restricted stock award activity during the three months ended March 31, 2017 is presented below: Awards Weighted Average Price Nonvested at December 31, 2016 325,643 $ 44.44 Restricted stock units granted 119,016 52.18 Vested (37,212 ) 70.62 Forfeited (1,934 ) 45.66 Nonvested at March 31, 2017 405,513 $ 44.30 Performance Share Awards: In addition, t he Stock Incentive Plan provides for the grant of performance share awards to eligible employees based on predetermined Energen performance criteria at the end of an award period. The Stock Incentive Plan provides that payment of earned performance share awards be made in the form of Energen common stock. Performance share awards are valued using the Monte Carlo model which uses historical volatility and other assumptions to estimate the probability of satisfying the market condition of the award and have a three -year vesting period. A summary of performance share award activity during the three months ended March 31, 2017 is presented below: Shares Weighted Average Price Nonvested at December 31, 2016 336,442 $ 57.03 Granted (three-year vesting period) 132,017 65.74 Vested and paid (59,530 ) 93.52 Forfeited (2,219 ) 48.45 Nonvested at March 31, 2017 406,710 $ 54.56 Stock Repurchase Program During the three months ended March 31, 2017 and 2016, Energen had non-cash purchases of approximately $3.2 million and $2.4 million , respectively, of Energen common stock in conjunction with tax withholdings on our non-qualified deferred compensation plan and other stock compensation. Energen utilized internally generated cash flows in payment of the related tax withholdings.

Employee Benefit Plans

Employee Benefit Plans	3 Months Ended
	Mar. 31, 2017
Compensation and Retirement Disclosure [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS In October 2014, Energen’s Board of Directors elected to freeze and terminate its qualified defined benefit pension plan. A plan amendment adopted in October 2014 closed the plan to new entrants, effective November 1, 2014, and froze benefit accruals effective December 31, 2014. Energen terminated the plan on January 31, 2015 and distributed benefits in December 2015. The Pension Benefit Guaranty Corporation (PBGC) is conducting an audit of the termination of the pension plan to ensure that Energen properly calculated and distributed benefits in accordance with plan provisions and in compliance with the appropriate laws and regulations administered by the PBGC. Energen’s non-qualified supplemental retirement plans were terminated effective December 31, 2014. Distributions under the plans were partially made in the first quarter of 2015 with the remainder of approximately $14.5 million paid in the first quarter of 2016. The Company expects to make no additional benefit payments with respect to the termination of the non-qualified supplemental retirement plans. Certain annuities associated with our non-qualified supplemental retirement plans remain of approximately $1.1 million and are included in other current liabilities and other long-term liabilities on the consolidated balance sheets at both March 31, 2017 and December 31, 2016. In the first quarter of 2016, Energen incurred a settlement charge of $3.3 million for the payment of lump sums from the non-qualified supplemental retirement plans. The components of net periodic postretirement benefit expense for Energen’s postretirement benefit plan were as follows: Three months ended (in thousands) 2017 2016 Components of net periodic benefit cost: Service cost $ 18 $ 23 Interest cost 57 66 Expected long-term return on assets (62 ) (111 ) Prior service cost amortization (114 ) (125 ) Actuarial loss amortization 2 — Settlement charge — 45 Curtailment gain — (816 ) Net periodic income $ (99 ) $ (918 ) There are no required contributions to the postretirement benefit plan during 2017. In the first quarter of 2016, Energen incurred a curtailment gain of $0.8 million in connection with the reduction in workforce.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Commitments and Agreements: Under various agreements for third-party gathering, treatment, transportation or other services, Energen is committed to deliver minimum production volumes or to pay certain costs in the event the minimum quantities are not delivered. These delivery commitments are approximately 3.9 million barrels of oil equivalent (MMBOE) through October 2020 . Legal Matters: Energen and its affiliates are, from time to time, parties to various pending or threatened legal proceedings and we have accrued a provision for our estimated liability. Certain of these lawsuits include claims for punitive damages in addition to other specified relief. We recognize a liability for contingencies, including an estimate of legal costs to be incurred, when information available indicates both a loss is probable and the amount of the loss can be reasonably estimated. Based upon information presently available, and in light of available legal and other defenses, contingent liabilities arising from threatened and pending litigation are not considered material in relation to the respective financial positions of Energen and its affiliates. It should be noted, however, that there is uncertainty in the valuation of pending claims and prediction of litigation results. On November 4, 2015, Energen Resources filed a quiet title action against Endeavor Energy Resources, L.P. (Endeavor) in the District Court of Howard County, Texas, to remove a cloud on the title to approximately 10,000 acres leased by Energen Resources in that county. Energen Resources believes the cloud on title arises from a prior, unreleased but partially terminated oil and gas lease covering the leased lands. Endeavor filed a counterclaim alleging Energen Resources tortiously interfered with a prospective contract seeking $300 million in damages. On April 28, 2016, the trial judge ruled with respect to the acreage not held by production that Endeavor’s lease terminated prior to the date Energen Resources entered into its lease and additionally ruled that Endeavor’s claim for tortuous interference will be dismissed with prejudice. The order left several ancillary issues for a later ruling. In November 2016, the trial judge entered a final and appealable judgment with respect to the remaining issues and that judgement has been appealed by Endeavor. Environmental Matters: Various environmental laws and regulations apply to the operations of Energen and Energen Resources. Historically, the cost of environmental compliance has not materially affected our financial position, results of operations or cash flows. New regulations, enforcement policies, claims for damages or other events could result in significant unanticipated costs. During January 2014, Energen Resources responded to a General Notice and Information Request from the Environmental Protection Agency regarding the Reef Environmental Site in Sylacauga, Talladega County, Alabama. The letter identifies Energen Resources as a potentially responsible party under The Comprehensive Environmental Response, Compensation, and Liability Act for the cleanup of the Site. In 2008, Energen hired a third party to transport approximately 3,000 gallons of non-hazardous wastewater to Reef Environmental for wastewater treatment. Reef Environmental ceased operating its wastewater treatment system in 2010. Due to its one time use of Reef Environmental for a small volume of non-hazardous wastewater, Energen Resources has not accrued a liability for cleanup of the Site. New Mexico Audits: In 2011, Energen Resources received an Order to Perform Restructured Accounting and Pay Additional Royalties (the Order), following an audit performed by the Taxation and Revenue Department (the Department) of the State of New Mexico on behalf of the Office of Natural Resources Revenue (ONRR), of federal oil and gas leases in New Mexico. The audit covered periods from January 2004 through December 2008 and included a review of the computation and payment of royalties due on minerals removed from specified U.S. federal leases. The Order addressed ONRR’s efforts to change accounting and reporting practices, and to unbundle fees charged by third parties that gather, compress and transport natural gas production. ONRR now maintains that all or some of such fees are not deductible. Energen Resources appealed the Order in 2011 and in July 2012, on a motion from ONRR, the Order was remanded. In August 2014, ONRR issued its Revised Order and Energen Resources appealed the Revised Order. In the Revised Order, ONRR ordered that Energen pay additional royalties on production from certain federal leases in the amount of $129,700 . At ONRR’s request the Revised Order was also remanded in August 2015. On April 15, 2016 ONRR issued its Second Revised Order. The Second Revised Order directs Energen Resources to pay additional royalties of $189,000 , replacing the previous demand of $129,700 . Energen had previously estimated that application of the ONRR position to all of the Company’s federal leases would result in ONRR claims up to approximately $24 million , plus interest and penalties from 2004 forward. ONRR began implementing its unbundling initiative in 2010, but seeks to implement its revisions retroactively, despite the fact that they conflict with previous audits, allowances and industry practice. Energen plans to appeal and vigorously contest the Second Revised Order, the predecessor orders and the findings. Management is unable, at this time, to determine a range of reasonably possible losses, and no amount has been accrued as of March 31, 2017 .

Exploratory Costs

Exploratory Costs	3 Months Ended
	Mar. 31, 2017
Extractive Industries [Abstract]
Exploratory Costs	EXPLORATORY COSTS Energen capitalizes exploratory drilling costs until a determination is made that the well or project has either found proved reserves or is impaired. After an exploratory well has been drilled and found oil and natural gas reserves, a determination may be pending as to whether the oil and natural gas quantities can be classified as proved. In those circumstances, Energen continues to capitalize the drilling costs pending the determination of proved status if (i) the well has found a sufficient quantity of reserves to justify its completion as a producing well and (ii) Energen is making sufficient progress assessing the reserves and the economic and operating viability of the project. Capitalized exploratory drilling costs are presented in proved properties in the balance sheets. If the exploratory well is determined to be a dry hole, the costs are charged to exploration expense. Other exploration costs, including geological and geophysical costs, are expensed as incurred. The following table sets forth capitalized exploratory well costs and includes additions pending determination of proved reserves, reclassifications to proved reserves and costs charged to expense: Three months ended (in thousands) 2017 2016 Capitalized exploratory well costs at beginning of period $ 164,996 $ 103,588 Additions pending determination of proved reserves 164,966 83,446 Reclassifications due to determination of proved reserves (161,697 ) (81,443 ) Capitalized exploratory well costs at end of period $ 168,265 $ 105,591 The following table sets forth capitalized exploratory well costs: (in thousands) March 31, 2017 December 31, 2016 Exploratory wells in progress (drilling rig not released) $ 11,234 $ 14,531 Capitalized exploratory well costs capitalized for a period of one year or less 150,131 143,602 Capitalized exploratory well costs for a period greater than one year 6,900 6,863 Total capitalized exploratory well costs $ 168,265 $ 164,996 At March 31, 2017 , Energen had 55 gross exploratory wells either drilling or waiting on results from completion and testing, 51 of which were located in the Permian Basin. As of March 31, 2017 and December 31, 2016, the Company had two gross wells capitalized greater than a year. These wells are scheduled for completion during 2017.

Asset Retirement Obligations

Asset Retirement Obligations	3 Months Ended
	Mar. 31, 2017
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS Energen’s asset retirement obligations (ARO) primarily relate to the future plugging, abandonment and reclamation of wells and facilities. We recognize a liability for the fair value of the ARO in the periods incurred. The ARO fair value liability is determined by calculating the present value of the estimated future cash outflows we expect to incur to plug, abandon and reclaim our producing properties at the end of their productive lives, and is recognized on a discounted basis incorporating an estimate of performance risk specific to Energen. Subsequent to initial measurement, liabilities are accreted to their present value and capitalized costs are depreciated over the estimated useful lives of the related assets. Upon settlement of the liability, Energen may recognize a gain or loss for differences between estimated and actual settlement costs. The following table reflects the components of the change in Energen’s ARO balance: (in thousands) Balance as of December 31, 2016 $ 81,544 Liabilities incurred 470 Liabilities settled (172 ) Accretion expense 1,414 Balance as of March 31, 2017 $ 83,256

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) The following table provides changes in the components of accumulated other comprehensive income (loss), net of the related income tax effects. (in thousands) Balance as of December 31, 2016 $ 1,405 Amounts reclassified from accumulated other comprehensive income (loss) (69 ) Balance as of March 31, 2017 $ 1,336 The following table provides details of the reclassifications out of accumulated other comprehensive income (loss). Three months ended March 31, 2017 2016 (in thousands) Amounts Reclassified Line Item Where Presented Pension and postretirement plans: Prior service cost $ 113 $ 125 General and administrative Actuarial losses (2 ) (3,058 ) General and administrative Total pension and postretirement plans 111 (2,933 ) Income tax expense (benefit) (42 ) 1,121 Total reclassifications for the period, net of tax $ 69 $ (1,812 )

Asset Impairment

Asset Impairment	3 Months Ended
	Mar. 31, 2017
Property, Plant and Equipment [Abstract]
Asset Impairment	ASSET IMPAIRMENT Impairments recognized by Energen are presented below: Three months ended (in thousands) 2017 2016 Permian Basin oil properties Central Basin Platform $ 1,096 $ 187,043 Delaware Basin — 21,288 San Juan Basin properties — 7,519 Permian Basin unproved leasehold properties 364 4,135 San Juan Basin unproved leasehold properties — 40 Total asset impairments $ 1,460 $ 220,025 Non-cash impairment writedowns are reflected in asset impairment on the consolidated statements of operations. Permian Basin: During the first quarter of 2017, Energen recognized non-cash impairment writedowns in the Permian Basin of $1.1 million to adjust the carrying amount of these properties to their fair value. During the first quarter of 2016, Energen recognized non-cash impairment writedowns in the Permian Basin of $208.3 million to adjust the carrying amount of these properties to their fair value. We estimate future discounted cash flows in determining fair value using commodity assumptions, which are based on the commodity price curve for five years and then escalated at 3 percent through our assumed price cap. Our commodity price assumptions declined in the first quarter of 2016 by approximately 5 percent for oil and 4 percent for natural gas in comparable periods. During the first quarter of 2017, Energen recognized unproved leasehold writedowns primarily on Permian Basin oil properties of $0.4 million . Energen recognized unproved leasehold writedowns primarily on Permian Basin oil properties in the Delaware Basin and the Central Basin Platform of $4.1 million in the first quarter of 2016. San Juan Basin: During the first quarter of 2016, Energen recognized non-cash impairment writedowns on held for sale properties in the San Juan Basin of $7.5 million to adjust the carrying amount of these properties to their fair value.

Acquisition and Disposition of

Acquisition and Disposition of Properties	3 Months Ended
	Mar. 31, 2017
Business Combinations [Abstract]
Acquisition and Disposition of Properties	ACQUISITION AND DISPOSITION OF PROPERTIES During June, July and August of 2016, Energen completed a series of asset sales of certain non-core Permian Basin assets in the Delaware Basin in Texas and in the San Juan Basin in New Mexico for an aggregate purchase price of $552 million . These transactions had closing dates of June 3, 7, 30, July 15 and August 9 of 2016 with various effective dates ranging from March 1, 2016 to June 30, 2016. Minor portions of the assets were transferred to other parties upon the exercise of preferential purchase rights under pre-existing joint operating agreements in the ordinary course of business. Pre-tax proceeds to Energen were approximately $532.6 million after purchase price adjustments of approximately $19 million related to the operations of the properties subsequent to the effective dates and other one-time adjustments including transfer payments and certain amounts due the buyer, but before consideration of transaction costs of approximately $5 million . Energen recognized pre-tax gains of $246 million on the sales. Energen used proceeds from the sale to fund ongoing operations. During the three months ended March 31, 2017, Energen completed an estimated total of $157.8 million in various purchases and renewals of unproved acquisitions including approximately $111.9 million in the Delaware Basin and approximately $27.1 million in the Midland Basin for unproved leasehold and $18.8 million for mineral purchases in the Delaware Basin. Energen completed an estimated $7.6 million in various purchases and renewals of unproved leasehold largely in the Permian Basin during the three months ended March 31, 2016.

Recently Issued Accounting Stan

Recently Issued Accounting Standards	3 Months Ended
	Mar. 31, 2017
Accounting Changes and Error Corrections [Abstract]
Recently Issued Accounting Standards	RECENTLY ISSUED ACCOUNTING STANDARDS In March 2017, the Financial Accounting Standards Board (FASB) issued Accounting Standard Update (ASU) No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. The amendments in this update require that the service cost component of net periodic postretirement benefit expense be presented in the same statement of operations line item as other employee compensation costs, while the remaining components of net periodic postretirement benefit expense are to be presented outside operating income. The amendment is effective for annual periods beginning after December 15, 2017, and interim periods within those annual years. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows - Classification of Certain Cash Receipts and Cash Payments. This update apples to all entities that are required to present a statement of cash flows. This update provides guidance on eight specific cash flow issues: debt prepayment or debt extinguishment costs, settlement of zero-coupon debt instruments or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, distributions received from equity method investees, beneficial interests in securitization transactions and separately identifiable cash flows and application of the predominance principle. This update will be effective for financial statements issued for fiscal years beginning after December 31, 2017, including interim periods within those fiscal years with early adoption permitted. This update should be applied using the retrospective transition method. Adoption of this standard will only affect the presentation of the Company’s cash flows and is not expected to have a material impact on the Company’s consolidated financial statements. In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting, which makes a number of changes meant to simplify and improve accounting for share-based payments. The amendment was effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. The adoption of this ASU effective January 1, 2017 did not have a material impact on our consolidated financial statements. Upon adoption of this new guidance, all excess tax benefits and tax deficiencies are recognized as income tax expense or benefit in our consolidated statements of operations as a discrete item in the reporting period in which they occur. The presentation requirements for cash flows related to employee taxes paid for withheld shares were adjusted retrospectively. These cash outflows, which were historically presented as an operating activity, were classified as a financing activity under taxes paid for shares withheld on the consolidated statements of cash flows. The Company also had an approximate $169,000 decrease to retained earnings associated with our election to recognize forfeitures as they occur. In February 2016, the FASB issued ASU No. 2016-02, Leases. This update increases transparency and comparability by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. The amendment is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. The primary effect of adopting the new standard will be to record assets and obligations on the balance sheet for contracts currently recognized as operating leases. We have identified certain applicable leases under the standard and are currently developing an inventory of all applicable leases. The Company is still evaluating the impact of this standard on our consolidated financial statements. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers. This update is based on the principle that revenue is recognized to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. It also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts. Companies may apply this update retrospectively or using a modified retrospective approach to adjust retained earnings. In August 2015, the FASB issued ASU No. 2015-14, Revenue from Contracts with Customers, which deferred the effective date of ASU No. 2014-09 to annual periods beginning after December 15, 2017, including interim reporting periods within that reporting period. The Company expects to adopt using the modified retrospective method of adoption on January 1, 2018. We continue to evaluate the impact of this standard on our individual customer contracts, however, due to the short length of our revenue cycle, we do not expect and have not identified any significant impacts to our consolidated financial statements.

Recently Issued Accounting St24

Recently Issued Accounting Standards (Policies)	3 Months Ended
	Mar. 31, 2017
Accounting Changes and Error Corrections [Abstract]
Recently Issued Accounting Standards	RECENTLY ISSUED ACCOUNTING STANDARDS In March 2017, the Financial Accounting Standards Board (FASB) issued Accounting Standard Update (ASU) No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. The amendments in this update require that the service cost component of net periodic postretirement benefit expense be presented in the same statement of operations line item as other employee compensation costs, while the remaining components of net periodic postretirement benefit expense are to be presented outside operating income. The amendment is effective for annual periods beginning after December 15, 2017, and interim periods within those annual years. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows - Classification of Certain Cash Receipts and Cash Payments. This update apples to all entities that are required to present a statement of cash flows. This update provides guidance on eight specific cash flow issues: debt prepayment or debt extinguishment costs, settlement of zero-coupon debt instruments or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, distributions received from equity method investees, beneficial interests in securitization transactions and separately identifiable cash flows and application of the predominance principle. This update will be effective for financial statements issued for fiscal years beginning after December 31, 2017, including interim periods within those fiscal years with early adoption permitted. This update should be applied using the retrospective transition method. Adoption of this standard will only affect the presentation of the Company’s cash flows and is not expected to have a material impact on the Company’s consolidated financial statements. In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting, which makes a number of changes meant to simplify and improve accounting for share-based payments. The amendment was effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. The adoption of this ASU effective January 1, 2017 did not have a material impact on our consolidated financial statements. Upon adoption of this new guidance, all excess tax benefits and tax deficiencies are recognized as income tax expense or benefit in our consolidated statements of operations as a discrete item in the reporting period in which they occur. The presentation requirements for cash flows related to employee taxes paid for withheld shares were adjusted retrospectively. These cash outflows, which were historically presented as an operating activity, were classified as a financing activity under taxes paid for shares withheld on the consolidated statements of cash flows. The Company also had an approximate $169,000 decrease to retained earnings associated with our election to recognize forfeitures as they occur. In February 2016, the FASB issued ASU No. 2016-02, Leases. This update increases transparency and comparability by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. The amendment is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. The primary effect of adopting the new standard will be to record assets and obligations on the balance sheet for contracts currently recognized as operating leases. We have identified certain applicable leases under the standard and are currently developing an inventory of all applicable leases. The Company is still evaluating the impact of this standard on our consolidated financial statements. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers. This update is based on the principle that revenue is recognized to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. It also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts. Companies may apply this update retrospectively or using a modified retrospective approach to adjust retained earnings. In August 2015, the FASB issued ASU No. 2015-14, Revenue from Contracts with Customers, which deferred the effective date of ASU No. 2014-09 to annual periods beginning after December 15, 2017, including interim reporting periods within that reporting period. The Company expects to adopt using the modified retrospective method of adoption on January 1, 2018. We continue to evaluate the impact of this standard on our individual customer contracts, however, due to the short length of our revenue cycle, we do not expect and have not identified any significant impacts to our consolidated financial statements.

Derivative Commodity Instrume25

Derivative Commodity Instruments (Tables)	3 Months Ended
	Mar. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Offsetting Liabilities	The following tables detail the offsetting of derivative assets and liabilities as well as the fair values of derivatives on the balance sheets: (in thousands) March 31, 2017 Gross Amounts Not Offset in the Balance Sheets Gross Amounts Recognized at Fair Value Gross Amounts Offset in the Balance Sheets Net Amounts Presented in the Balance Sheets Financial Instruments Cash Collateral Received Net Fair Value Presented in the Balance Sheets Derivatives not designated as hedging instruments Assets Derivative instruments $ 14,651 $ (7,057 ) $ 7,594 $ — $ — $ 7,594 Noncurrent derivative instruments 9,375 (82 ) 9,293 — — 9,293 Total derivative assets 24,026 (7,139 ) 16,887 — — 16,887 Liabilities Derivative instruments 15,381 (7,057 ) 8,324 — — 8,324 Noncurrent derivative instruments 82 (82 ) — — — — Total derivative liabilities 15,463 (7,139 ) 8,324 — — 8,324 Total derivatives $ 8,563 $ — $ 8,563 $ — $ — $ 8,563 (in thousands) December 31, 2016 Gross Amounts Not Offset in the Balance Sheets Gross Amounts Recognized at Fair Value Gross Amounts Offset in the Balance Sheets Net Amounts Presented in the Balance Sheets Financial Instruments Cash Collateral Received Net Fair Value Presented in the Balance Sheets Derivatives not designated as hedging instruments Assets Derivative instruments $ 1,756 $ (1,706 ) $ 50 $ — $ — $ 50 Liabilities Derivative instruments 67,173 (1,706 ) 65,467 — — 65,467 Noncurrent derivative instruments 3,006 — 3,006 — — 3,006 Total derivatives $ (68,423 ) $ — $ (68,423 ) $ — $ — $ (68,423 )
Schedule of Offsetting Assets	The following tables detail the offsetting of derivative assets and liabilities as well as the fair values of derivatives on the balance sheets: (in thousands) March 31, 2017 Gross Amounts Not Offset in the Balance Sheets Gross Amounts Recognized at Fair Value Gross Amounts Offset in the Balance Sheets Net Amounts Presented in the Balance Sheets Financial Instruments Cash Collateral Received Net Fair Value Presented in the Balance Sheets Derivatives not designated as hedging instruments Assets Derivative instruments $ 14,651 $ (7,057 ) $ 7,594 $ — $ — $ 7,594 Noncurrent derivative instruments 9,375 (82 ) 9,293 — — 9,293 Total derivative assets 24,026 (7,139 ) 16,887 — — 16,887 Liabilities Derivative instruments 15,381 (7,057 ) 8,324 — — 8,324 Noncurrent derivative instruments 82 (82 ) — — — — Total derivative liabilities 15,463 (7,139 ) 8,324 — — 8,324 Total derivatives $ 8,563 $ — $ 8,563 $ — $ — $ 8,563 (in thousands) December 31, 2016 Gross Amounts Not Offset in the Balance Sheets Gross Amounts Recognized at Fair Value Gross Amounts Offset in the Balance Sheets Net Amounts Presented in the Balance Sheets Financial Instruments Cash Collateral Received Net Fair Value Presented in the Balance Sheets Derivatives not designated as hedging instruments Assets Derivative instruments $ 1,756 $ (1,706 ) $ 50 $ — $ — $ 50 Liabilities Derivative instruments 67,173 (1,706 ) 65,467 — — 65,467 Noncurrent derivative instruments 3,006 — 3,006 — — 3,006 Total derivatives $ (68,423 ) $ — $ (68,423 ) $ — $ — $ (68,423 )
Effects of Open and Closed Derivative Commodity Instruments Not Designated as Hedging Instruments	The following table details the effect of open and closed derivative commodity instruments not designated as hedging instruments on the statements of operations: (in thousands) Location on Statements of Operations Three months Three months Gain recognized in income on derivatives Gain on derivative instruments, net $ 64,546 $ 5,455
Schedule of Hedging Transactions	As of March 31, 2017, Energen had entered into the following transactions for the remainder of 2017 and subsequent years: Production Period Description Total Hedged Volumes Average Contract Price Oil 2017 NYMEX Swaps 5,040 MBbl $50.13 Bbl NYMEX Three-Way Collars 3,600 MBbl Ceiling sold price (call) $62.18 Bbl Floor purchased price (put) $45.00 Bbl Floor sold price (put) $35.00 Bbl 2018 NYMEX Three-Way Collars 5,940 MBbl Ceiling sold price (call) $65.05 Bbl Floor purchased price (put) $50.00 Bbl Floor sold price (put) $40.00 Bbl Oil Basis Differential 2017 WTI/WTI Basis Swaps 7,560 MBbl $(0.64) Bbl 2018 WTI/WTI Basis Swaps 3,240 MBbl $(1.12) Bbl Natural Gas Liquids 2017 Liquids Swaps 62.4 MMGal $0.57 Gal 2018 Liquids Swaps 75.6 MMGal $0.60 Gal Natural Gas 2017 Basin Specific Swaps - Permian 11.4 Bcf $2.85 Mcf 2017 NYMEX Swaps 0.9 Bcf $3.29 Mcf Natural Gas Basis Differential 2017 Permian Swaps 0.9 Bcf $(0.29) Mcf WTI - West Texas Intermediate/Midland, WTI - West Texas Intermediate/Cushing

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following fair value hierarchy tables present information about Energen’s assets and liabilities measured at fair value on a recurring basis: March 31, 2017 (in thousands) Level 2 Level 3 Total Assets: Derivative instruments $ 3,879 $ 3,715 $ 7,594 Noncurrent derivative instruments 7,434 1,859 9,293 Total assets 11,313 5,574 16,887 Liabilities: Derivative instruments (8,324 ) — (8,324 ) Net derivative asset $ 2,989 $ 5,574 $ 8,563 December 31, 2016 (in thousands) Level 2 Level 3 Total Assets: Derivative instruments $ 50 $ — $ 50 Liabilities: Derivative instruments (57,927 ) (7,540 ) (65,467 ) Noncurrent derivative instruments (1,694 ) (1,312 ) (3,006 ) Total liabilities (59,621 ) (8,852 ) (68,473 ) Net derivative liability $ (59,571 ) $ (8,852 ) $ (68,423 )
Schedule of Changes in Fair Value of Derivative Commodity Instruments	The table below sets forth a summary of changes in the fair value of Energen’s Level 3 derivative commodity instruments as follows: Three months ended March 31, (in thousands) 2017 2016 Balance at beginning of period $ (8,852 ) $ (16,059 ) Realized losses (3,253 ) (5,518 ) Unrealized gains relating to instruments held at the reporting date* 14,416 7,905 Settlements during period 3,263 5,518 Balance at end of period $ 5,574 $ (8,154 ) *Includes $10.9 million and $2.2 million in mark-to-market gains for the three months ended March 31, 2017 and 2016, respectively.
Quantitative Information About Level 3 Fair Value Measurements of Derivative Commodity Instruments	The table below sets forth quantitative information about Energen’s Level 3 fair value measurements of derivative commodity instruments as follows: (in thousands, except price data) Fair Value as of March 31, 2017 Valuation Technique* Unobservable Input* Range Oil Basis - WTI/WTI 2017 $ 4,538 Discounted Cash Flow Forward Basis $(1.35 - $1.29) Bbl 2018 $ 806 Discounted Cash Flow Forward Basis ($1.40 - $1.35) Bbl Natural Gas Liquids 2017 $ (935 ) Discounted Cash Flow Forward Basis $0.59 Gal 2018 $ 1,165 Discounted Cash Flow Forward Basis $0.58 Gal *Discounted cash flow represents an income approach in calculating fair value including the referenced unobservable input and a discount reflecting credit quality of the counterparty.

Long-Term Debt (Tables)

Long-Term Debt (Tables)	3 Months Ended
	Mar. 31, 2017
Debt Disclosure [Abstract]
Schedule of Long-Term Debt	Long-term debt consisted of the following: (in thousands) March 31, 2017 December 31, 2016 7.40% Medium-term Notes, Series A, due July 24, 2017 $ — $ 2,000 7.36% Medium-term Notes, Series A, due July 24, 2017 15,000 15,000 7.23% Medium-term Notes, Series A, due July 28, 2017 2,000 2,000 7.32% Medium-term Notes, Series A, due July 28, 2022 20,000 20,000 7.60% Medium-term Notes, Series A, due July 26, 2027 — 5,000 7.35% Medium-term Notes, Series A, due July 28, 2027 10,000 10,000 7.125% Medium-term Notes, Series B, due February 15, 2028 100,000 100,000 4.625% Notes, due September 1, 2021 400,000 400,000 Total 547,000 554,000 Less amounts due within one year 17,000 24,000 Less unamortized debt discount 381 387 Less unamortized debt issuance costs 2,062 2,170 Total $ 527,557 $ 527,443
Maturities of Long-term Debt	The aggregate maturities of Energen’s long-term debt outstanding at March 31, 2017 are as follows: (in thousands) Remaining 2017 2018 2019 2020 2021 2022 and thereafter $17,000 $— $— $— $400,000 $130,000
Summary of Credit Facilities	The following is a summary of information relating to Energen’s credit facility: (in thousands) March 31, 2017 December 31, 2016 Credit facility outstanding $ — $ — Available for borrowings 1,050,000 1,050,000 Total borrowing commitments $ 1,050,000 $ 1,050,000 Three months ended 2017 2016 Maximum amount outstanding at any month-end $ — $ 214,500 Average daily amount outstanding $ 28 $ 134,934 Weighted average interest rates based on: Average daily amount outstanding 2.05 % 1.72 % Amount outstanding at period-end — % — %

Reconciliation of Earnings Pe28

Reconciliation of Earnings Per Share (EPS) (Tables)	3 Months Ended
	Mar. 31, 2017
Earnings Per Share [Abstract]
Schedule of Earnings Per Share Reconciliation	Three months ended Three months ended (in thousands, except per share amounts) March 31, 2017 March 31, 2016 Net Per Share Net Per Share Income Shares Amount Loss Shares Amount Basic EPS $ 33,403 97,140 $ 0.34 $ (203,116 ) 86,632 $ (2.34 ) Effect of dilutive securities Stock options 31 — Non-vested restricted stock 262 — Performance share awards 174 — Diluted EPS $ 33,403 97,607 $ 0.34 $ (203,116 ) 86,632 $ (2.34 )
Schedule of Shares Excluded from the Computation of Diluted EPS	Energen had the following shares that were excluded from the computation of diluted EPS, as inclusion would be anti-dilutive: Three months ended (in thousands) 2017 2016 Stock options 267 — Performance share awards 131 —

Stock Compensation (Tables)

Stock Compensation (Tables)	3 Months Ended
	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Compensation, Stock Options, Activity	A summary of restricted stock award activity during the three months ended March 31, 2017 is presented below: Awards Weighted Average Price Nonvested at December 31, 2016 325,643 $ 44.44 Restricted stock units granted 119,016 52.18 Vested (37,212 ) 70.62 Forfeited (1,934 ) 45.66 Nonvested at March 31, 2017 405,513 $ 44.30 A summary of performance share award activity during the three months ended March 31, 2017 is presented below: Shares Weighted Average Price Nonvested at December 31, 2016 336,442 $ 57.03 Granted (three-year vesting period) 132,017 65.74 Vested and paid (59,530 ) 93.52 Forfeited (2,219 ) 48.45 Nonvested at March 31, 2017 406,710 $ 54.56

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2017
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Schedule of Net Periodic Benefit Costs	The components of net periodic postretirement benefit expense for Energen’s postretirement benefit plan were as follows: Three months ended (in thousands) 2017 2016 Components of net periodic benefit cost: Service cost $ 18 $ 23 Interest cost 57 66 Expected long-term return on assets (62 ) (111 ) Prior service cost amortization (114 ) (125 ) Actuarial loss amortization 2 — Settlement charge — 45 Curtailment gain — (816 ) Net periodic income $ (99 ) $ (918 )

Exploratory Costs (Tables)

Exploratory Costs (Tables)	3 Months Ended
	Mar. 31, 2017
Extractive Industries [Abstract]
Schedule of Capitalized Exploratory Wells	The following table sets forth capitalized exploratory well costs and includes additions pending determination of proved reserves, reclassifications to proved reserves and costs charged to expense: Three months ended (in thousands) 2017 2016 Capitalized exploratory well costs at beginning of period $ 164,996 $ 103,588 Additions pending determination of proved reserves 164,966 83,446 Reclassifications due to determination of proved reserves (161,697 ) (81,443 ) Capitalized exploratory well costs at end of period $ 168,265 $ 105,591 The following table sets forth capitalized exploratory well costs: (in thousands) March 31, 2017 December 31, 2016 Exploratory wells in progress (drilling rig not released) $ 11,234 $ 14,531 Capitalized exploratory well costs capitalized for a period of one year or less 150,131 143,602 Capitalized exploratory well costs for a period greater than one year 6,900 6,863 Total capitalized exploratory well costs $ 168,265 $ 164,996

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	3 Months Ended
	Mar. 31, 2017
Asset Retirement Obligation Disclosure [Abstract]
Schedule of Components of the Change in the ARO Balance	The following table reflects the components of the change in Energen’s ARO balance: (in thousands) Balance as of December 31, 2016 $ 81,544 Liabilities incurred 470 Liabilities settled (172 ) Accretion expense 1,414 Balance as of March 31, 2017 $ 83,256

Accumulated Other Comprehensi33

Accumulated Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
Schedule of Changes in Components of Accumulated Other Comprehensive Income (Loss), Net of Related Income Tax Effects	The following table provides changes in the components of accumulated other comprehensive income (loss), net of the related income tax effects. (in thousands) Balance as of December 31, 2016 $ 1,405 Amounts reclassified from accumulated other comprehensive income (loss) (69 ) Balance as of March 31, 2017 $ 1,336
Reclassification Out of Accumulated Other Comprehensive Income (Loss)	The following table provides details of the reclassifications out of accumulated other comprehensive income (loss). Three months ended March 31, 2017 2016 (in thousands) Amounts Reclassified Line Item Where Presented Pension and postretirement plans: Prior service cost $ 113 $ 125 General and administrative Actuarial losses (2 ) (3,058 ) General and administrative Total pension and postretirement plans 111 (2,933 ) Income tax expense (benefit) (42 ) 1,121 Total reclassifications for the period, net of tax $ 69 $ (1,812 )

Asset Impairment (Tables)

Asset Impairment (Tables)	3 Months Ended
	Mar. 31, 2017
Property, Plant and Equipment [Abstract]
Summary of Impairments Recognized	Impairments recognized by Energen are presented below: Three months ended (in thousands) 2017 2016 Permian Basin oil properties Central Basin Platform $ 1,096 $ 187,043 Delaware Basin — 21,288 San Juan Basin properties — 7,519 Permian Basin unproved leasehold properties 364 4,135 San Juan Basin unproved leasehold properties — 40 Total asset impairments $ 1,460 $ 220,025

Organization and Basis of Pre35

Organization and Basis of Presentation (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
One-time Termination Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring charges incurred for one-time termination benefits	$ 5

Derivative Commodity Instrume36

Derivative Commodity Instruments - Offsetting Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Assets
Gross Amounts Recognized at Fair Value	$ 24,026
Gross Amounts Offset in the Balance Sheets	(7,139)
Net Amounts Presented in the Balance Sheets	16,887
Financial Instruments	0
Cash Collateral Received	0
Net Fair Value Presented in the Balance Sheets	16,887
Liabilities
Gross Amounts Recognized at Fair Value	15,463
Gross Amounts Offset in the Balance Sheets	(7,139)
Net Amount Presented in the Balance Sheets	8,324
Financial Instruments	0
Cash Collateral Received	0
Net Fair Value Presented in the Balance Sheets	8,324
Total Derivatives	8,563	$ (68,423)
Current Assets
Assets
Gross Amounts Recognized at Fair Value	14,651	1,756
Gross Amounts Offset in the Balance Sheets	(7,057)	(1,706)
Net Amounts Presented in the Balance Sheets	7,594	50
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Fair Value Presented in the Balance Sheets	7,594	50
Noncurrent Assets
Assets
Gross Amounts Recognized at Fair Value	9,375
Gross Amounts Offset in the Balance Sheets	(82)
Net Amounts Presented in the Balance Sheets	9,293
Financial Instruments	0
Cash Collateral Received	0
Net Fair Value Presented in the Balance Sheets	9,293
Current Liabilities
Liabilities
Gross Amounts Recognized at Fair Value	15,381	67,173
Gross Amounts Offset in the Balance Sheets	(7,057)	(1,706)
Net Amount Presented in the Balance Sheets	8,324	65,467
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Fair Value Presented in the Balance Sheets	8,324	65,467
Noncurrent Liabilities
Liabilities
Gross Amounts Recognized at Fair Value	82	3,006
Gross Amounts Offset in the Balance Sheets	(82)	0
Net Amount Presented in the Balance Sheets	0	3,006
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Fair Value Presented in the Balance Sheets	$ 0	$ 3,006

Derivative Commodity Instrume37

Derivative Commodity Instruments - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Derivative [Line Items]
Gain on fair value of derivatives	$ 64,546	$ 5,455
Commodity contracts | J Aron And Company
Derivative [Line Items]
Gain on fair value of derivatives	2,400
Commodity contracts | J.P. Morgan Ventures Energy Corporation.
Derivative [Line Items]
Gain on fair value of derivatives	2,100
Commodity contracts | Merrill Lynch Commodities, Inc.
Derivative [Line Items]
Gain on fair value of derivatives	$ 1,900

Derivative Commodity Instrume38

Derivative Commodity Instruments - Not Designated as Hedging Instruments on the Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on fair value of derivatives	$ 64,546	$ 5,455
Gain on derivative instruments, net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on fair value of derivatives	$ 64,546	$ 5,455

Derivative Commodity Instrume39

Derivative Commodity Instruments - Derivative Transactions (Details)	3 Months Ended
	Mar. 31, 2017MBblsBcfMMgals$ / Mcf$ / bbl$ / gal
2017 | NYMEX Swaps | Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, Mmgal and Bcf) | MBbls	5,040
Average Contract Price (dollars per Bbl)	50.13
2017 | NYMEX Swaps | Natural Gas
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, Mmgal and Bcf) | MBbls	0.9
Average Contract Price (dollars per Bbl)	3.29
2017 | NYMEX Three-Way Collars | Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, Mmgal and Bcf) | MBbls	3,600
2017 | Ceiling sold price (call) | Crude Oil | Short
Derivatives, Fair Value [Line Items]
Ceiling sold price (call) (dollars per Bbl)	62.18
2017 | Floor Purchased and Sold Price (Put) | Crude Oil | Short
Derivatives, Fair Value [Line Items]
Floor price (dollars per Bbl)	35
2017 | Floor Purchased and Sold Price (Put) | Crude Oil | Long
Derivatives, Fair Value [Line Items]
Floor price (dollars per Bbl)	45
2017 | WTI/WTI Basis Swaps | Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, Mmgal and Bcf) | MBbls	7,560
Average Contract Price (dollars per Bbl)	(0.64)
2017 | Liquids Swaps | Natural Gas Liquids
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, Mmgal and Bcf) | MMgals	62.4
Average Contract Price (dollars per Bbl) | $ / gal	0.57
2017 | Basin Specific Swaps - Permian | Natural Gas
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, Mmgal and Bcf) | Bcf	11.4
Average Contract Price (dollars per Bbl) | $ / Mcf	2.85
2017 | Permian Swaps | Natural Gas Basis Differential
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, Mmgal and Bcf) | Bcf	0.9
Average Contract Price (dollars per Bbl) | $ / Mcf	(0.29)
2018 | NYMEX Three-Way Collars | Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, Mmgal and Bcf) | MBbls	5,940
2018 | Ceiling sold price (call) | Crude Oil | Short
Derivatives, Fair Value [Line Items]
Ceiling sold price (call) (dollars per Bbl)	65.05
2018 | Floor Purchased and Sold Price (Put) | Crude Oil | Short
Derivatives, Fair Value [Line Items]
Floor price (dollars per Bbl)	40
2018 | Floor Purchased and Sold Price (Put) | Crude Oil | Long
Derivatives, Fair Value [Line Items]
Floor price (dollars per Bbl)	50
2018 | WTI/WTI Basis Swaps | Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, Mmgal and Bcf) | MBbls	3,240
Average Contract Price (dollars per Bbl)	(1.12)
2018 | Liquids Swaps | Natural Gas Liquids
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl, Mmgal and Bcf) | MMgals	75.6
Average Contract Price (dollars per Bbl) | $ / gal	0.60

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Assets:
Noncurrent derivative instruments	$ 9,293	$ 0
Net Amounts Presented in the Balance Sheets	16,887
Liabilities:
Total liabilities	(8,324)
Recurring
Assets:
Derivative instruments	7,594	50
Noncurrent derivative instruments	9,293
Net Amounts Presented in the Balance Sheets	16,887
Liabilities:
Derivative instruments	(8,324)	(65,467)
Noncurrent derivative instruments		(3,006)
Total liabilities		(68,473)
Net derivative liability	8,563	(68,423)
Recurring | Level 2
Assets:
Derivative instruments	3,879	50
Noncurrent derivative instruments	7,434
Net Amounts Presented in the Balance Sheets	11,313
Liabilities:
Derivative instruments	(8,324)	(57,927)
Noncurrent derivative instruments		(1,694)
Total liabilities		(59,621)
Net derivative liability	2,989	(59,571)
Recurring | Level 3
Assets:
Derivative instruments	3,715	0
Noncurrent derivative instruments	1,859
Net Amounts Presented in the Balance Sheets	5,574
Liabilities:
Derivative instruments	0	(7,540)
Noncurrent derivative instruments		(1,312)
Total liabilities		(8,852)
Net derivative liability	$ 5,574	$ (8,852)

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowance for doubtful accounts	$ 600	$ 600
Long-term debt carrying value	547,000	554,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Sensitivity analysis of fair value of 10 percent change in commodity prices	6,500
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt fair value	548,500	559,900
Reported Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt carrying value	$ 547,000	$ 554,000

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Changes of Derivative Commodity Instruments in Fair Value (Details) - Derivative Commodity Instruments - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ (8,852)	$ (16,059)
Realized losses	(3,253)	(5,518)
Unrealized gains (losses) relating to instruments held at the reporting date	14,416	7,905
Settlements during period	3,263	5,518
Balance at end of period	5,574	(8,154)
Mark-to-market loss included in earnings	$ 10,900	$ 2,200

Fair Value Measurements - Level

Fair Value Measurements - Level 3 Measurements of Derivative Commodity Instruments (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017USD ($)$ / bblgal
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative Asset	$ 16,887
Derivative liabilities	(8,324)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2017
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative Asset	$ 4,538
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2017 | Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel (in dollars per Bbl and gal) | $ / bbl	(1.35)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2017 | Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel (in dollars per Bbl and gal) | $ / bbl	(1.29)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2018
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative Asset	$ (806)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2018 | Minimum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel (in dollars per Bbl and gal) | $ / bbl	(1.40)
Discounted Cash Flow Valuation Technique | Level 3 | Oil Basis - WTI/WTI | 2018 | Maximum
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Price per barrel (in dollars per Bbl and gal) | $ / bbl	(1.35)
Discounted Cash Flow Valuation Technique | Level 3 | Natural Gas Liquids | 2017
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative liabilities	$ (935)
Price per barrel (in dollars per Bbl and gal) | gal	0.59
Discounted Cash Flow Valuation Technique | Level 3 | Natural Gas Liquids | 2018
Fair Value Inputs, Derivatives, Quantitative Information [Line Items]
Derivative Asset	$ (1,165)
Price per barrel (in dollars per Bbl and gal) | gal	0.58

Long-Term Debt - Schedule of Lo

Long-Term Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Gross amount	$ 547,000	$ 554,000
Less amounts due within one year	17,000	24,000
Less unamortized debt discount	381	387
Less unamortized debt issuance costs	2,062	2,170
Total	527,557	527,443
Medium-term Notes | 7.40% Medium-term Notes, Series A, due July 24, 2017
Debt Instrument [Line Items]
Gross amount	$ 0	$ 2,000
Stated interest rate	7.40%	7.40%
Medium-term Notes | 7.36% Medium-term Notes, Series A, due July 24, 2017
Debt Instrument [Line Items]
Gross amount	$ 15,000	$ 15,000
Stated interest rate	7.36%	7.36%
Medium-term Notes | 7.23% Medium-term Notes, Series A, due July 28, 2017
Debt Instrument [Line Items]
Gross amount	$ 2,000	$ 2,000
Stated interest rate	7.23%	7.23%
Medium-term Notes | 7.32% Medium-term Notes, Series A, due July 28, 2022
Debt Instrument [Line Items]
Gross amount	$ 20,000	$ 20,000
Stated interest rate	7.32%	7.32%
Medium-term Notes | 7.60% Medium-term Notes, Series A, due July 26, 2027
Debt Instrument [Line Items]
Gross amount	$ 0	$ 5,000
Stated interest rate	7.60%	7.60%
Medium-term Notes | 7.35% Medium-term Notes, Series A, due July 28, 2027
Debt Instrument [Line Items]
Gross amount	$ 10,000	$ 10,000
Stated interest rate	7.35%	7.35%
Medium-term Notes | 7.125% Medium-term Notes, Series B, due February 15, 2028
Debt Instrument [Line Items]
Gross amount	$ 100,000	$ 100,000
Stated interest rate	7.125%	7.125%
Notes Payable | 4.625% Notes, due September 1, 2021
Debt Instrument [Line Items]
Gross amount	$ 400,000	$ 400,000
Stated interest rate	4.625%	4.625%

Long-Term Debt - Maturities of

Long-Term Debt - Maturities of Long-Term Debt (Details) $ in Thousands	Mar. 31, 2017USD ($)
Debt Disclosure [Abstract]
Remaining 2,017	$ 17,000
2,018	0
2,019	0
2,020	0
2,021	400,000
2022 and thereafter	$ 130,000

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Details) - USD ($)	Sep. 02, 2014	Mar. 31, 2017	Mar. 31, 2016	Jul. 23, 2017	Apr. 21, 2017	Dec. 31, 2016	Oct. 25, 2016
Debt Instrument [Line Items]
Gross amount		$ 547,000,000				$ 554,000,000
Cross default provision, threshold amount		10,000,000
Initial borrowing base		$ 1,050,000,000				1,050,000,000
Loan limit percentage (less than)		10.00%
Credit facility cross default provision, threshold amount		$ 75,000,000
Interest expense		8,966,000	$ 9,833,000
Debt issuance costs related to long-term debt		800,000	800,000
Capitalized interest expense		$ 0	0
Commitment fee (basis points)		0.30%
Debt related commitment fees		$ 800,000	$ 1,000,000
Medium-term Notes | 7.40% Medium-term Notes, Series A, due July 24, 2017
Debt Instrument [Line Items]
Gross amount		$ 0				$ 2,000,000
Stated interest rate		7.40%				7.40%
Medium-term Notes | 7.60% Medium-term Notes, Series A, due July 26, 2027
Debt Instrument [Line Items]
Gross amount		$ 0				$ 5,000,000
Stated interest rate		7.60%				7.60%
Credit facility
Debt Instrument [Line Items]
Initial borrowing base							$ 1,050,000,000
Syndicated Credit Facility | Credit Facility, September 2, 2014
Debt Instrument [Line Items]
Term of credit facility	5 years
Debt covenant, debt to EBITDAX ratio (less than or equal to)		4
Debt covenant, current assets to current liabilities ratio (greater than or equal to)		1
Debt covenant, minimum net present value of proved reserves to consolidated debt, ratio (greater than or equal to)		1.50
Subsequent Event | Credit facility
Debt Instrument [Line Items]
Initial borrowing base					$ 1,400,000,000
Scenario, Forecast | Medium-term Notes | 7.40% Medium-term Notes, Series A, due July 24, 2017
Debt Instrument [Line Items]
Gross amount				$ 2,000,000
Stated interest rate				7.40%
Scenario, Forecast | Medium-term Notes | 7.60% Medium-term Notes, Series A, due July 26, 2027
Debt Instrument [Line Items]
Gross amount				$ 5,000,000
Stated interest rate				7.60%

Long-Term Debt - Credit Facilit

Long-Term Debt - Credit Facilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Debt Disclosure [Abstract]
Credit facility outstanding	$ 0		$ 0
Available for borrowings	1,050,000		1,050,000
Total borrowing commitments	1,050,000		$ 1,050,000
Maximum amount outstanding at any month-end	0	$ 214,500
Average daily amount outstanding	$ 28	$ 134,934
Average daily amount outstanding (percent)	2.05%	1.72%
Amount outstanding at period-end (percent)	0.00%	0.00%

Reconciliation of Earnings Pe48

Reconciliation of Earnings Per Share (EPS) - Earnings Per Share Reconciliation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income (Loss), Basic EPS	$ 33,403	$ (203,116)
Basic Average Common Shares Outstanding (in shares)	97,140	86,632
Earnings Per Share, Basic (in dollars per share)	$ 0.34	$ (2.34)
Effect of dilutive securities
Net Income (Loss), Diluted EPS	$ 33,403	$ (203,116)
Diluted Average Common Shares Outstanding (in shares)	97,607	86,632
Earnings Per Share, Diluted (in dollars per share)	$ 0.34	$ (2.34)
Stock options
Effect of dilutive securities
Effect of dilutive securities (in shares)	31	0
Non-vested restricted stock
Effect of dilutive securities
Effect of dilutive securities (in shares)	262	0
Performance share awards
Effect of dilutive securities
Effect of dilutive securities (in shares)	174	0

Reconciliation of Earnings Pe49

Reconciliation of Earnings Per Share (EPS) - Antidilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)		233,547
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	267,000	0
Performance share awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	131,000	0

Equity Offering (Details)

Equity Offering (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Class of Stock [Line Items]
Issuance of common stock, net	$ 381.1
Common Stock
Class of Stock [Line Items]
Shares issued through public equity offering (in shares)		18,170,000

Stock Compensation (Details)

Stock Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award
Noncash payments for repurchase of common stock	$ 3.2	$ 2.4
Stock Incentive Plan | Performance share awards
Share-based Compensation Arrangement by Share-based Payment Award
Grants in period (in shares)	132,017
Weighted average grant date fair value (in dollars per share)	$ 65.74
Stock Incentive Plan | Performance share awards | 3 year vesting period
Share-based Compensation Arrangement by Share-based Payment Award
Vesting period		3 years

Stock Compensation - Summary of

Stock Compensation - Summary of Stock Option Activity (Details)	3 Months Ended
	Mar. 31, 2017$ / sharesshares
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares) | shares	325,643
Restricted stock units granted (in shares) | shares	119,016
Vested (in shares) | shares	(37,212)
Forfeited (in shares) | shares	(1,934)
Ending balance (in shares) | shares	405,513
Weighted Average Price
Beginning balance (in dollars per share) | $ / shares	$ 44.44
Granted (in dollars per share) | $ / shares	52.18
Vested (in dollars per share) | $ / shares	70.62
Forfeited (in dollars per share) | $ / shares	45.66
Ending balance (in dollars per share) | $ / shares	$ 44.30
Performance share awards
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares) | shares	336,442
Vested (in shares) | shares	(59,530)
Forfeited (in shares) | shares	(2,219)
Ending balance (in shares) | shares	406,710
Weighted Average Price
Beginning balance (in dollars per share) | $ / shares	$ 57.03
Vested (in dollars per share) | $ / shares	93.52
Forfeited (in dollars per share) | $ / shares	48.45
Ending balance (in dollars per share) | $ / shares	$ 54.56
Stock Incentive Plan | Performance share awards
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Restricted stock units granted (in shares) | shares	132,017
Weighted Average Price
Granted (in dollars per share) | $ / shares	$ 65.74

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Non-qualified supplemental retirement plan	$ 1,100,000		$ 1,100,000
Non-Qualified Supplemental Employee Retirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions by employer		$ 14,500,000
Estimated amount of additional benefit payments	0
Settlement charge		3,300,000
Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Curtailment gain	$ 0	$ 816,000

Employee Benefit Plans - Compon

Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - Postretirement Benefit Plans - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Components of net periodic benefit cost:
Service cost	$ 18	$ 23
Interest cost	57	66
Expected long-term return on assets	(62)	(111)
Prior service cost amortization	(114)	(125)
Actuarial loss	2	0
Settlement charge	0	45
Curtailment gain	0	(816)
Net periodic (income) expense	$ (99)	$ (918)

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) gal in Thousands, a in Thousands, MMBoe in Millions, $ in Millions	Nov. 04, 2015USD ($)a	Dec. 31, 2008gal	Mar. 31, 2017MMBoe
Sylacauga, Talladega County, Alabama
Long-term Purchase Commitment [Line Items]
Gallons of wastewater transported | gal		3
Crude Oil and Natural Gas
Long-term Purchase Commitment [Line Items]
Delivery commitments (MMBOE) | MMBoe			3.9
Endeavor Energy Resources | Pending Litigation
Long-term Purchase Commitment [Line Items]
Number of acres with cloud on the title | a	10
Damages sought | $	$ 300

Commitments and Contingencies56

Commitments and Contingencies - New Mexico Audits (Details) - USD ($)	Apr. 15, 2016	Aug. 31, 2014	Dec. 31, 2011
Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss	$ 189,000	$ 129,700	$ 24,000,000

Exploratory Costs (Details)

Exploratory Costs (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017USD ($)well	Mar. 31, 2016USD ($)well	Dec. 31, 2016USD ($)
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Capitalized exploratory well costs at beginning of period	$ 164,996	$ 103,588
Additions pending determination of proved reserves	164,966	83,446
Reclassifications due to determination of proved reserves	(161,697)	(81,443)
Capitalized exploratory well costs at end of period	168,265	$ 105,591
Capitalized Costs, Oil and Gas Producing Activities, Gross [Abstract]
Exploratory wells in progress (drilling rig not released)	11,234		$ 14,531
Capitalized exploratory well costs capitalized for a period of one year or less	150,131		143,602
Capitalized exploratory well costs for a period greater than one year	6,900		6,863
Total capitalized exploratory well costs	$ 168,265		$ 164,996
Number of wells in process of drilling | well	55
Number of wells capitalized | well		2

Asset Retirement Obligations (D

Asset Retirement Obligations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of December 31, 2016	$ 81,544
Liabilities incurred	470
Liabilities settled	(172)
Accretion expense	1,414	$ 1,757
Balance as of March 31, 2017	$ 83,256

Accumulated Other Comprehensi59

Accumulated Other Comprehensive Income (Loss) - Rollforward of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Amounts reclassified from accumulated other comprehensive income (loss)	$ (69)	$ 1,812
AOCI Including Portion Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	1,405
Ending balance	$ 1,336

Accumulated Other Comprehensi60

Accumulated Other Comprehensive Income (Loss) - Reclassifications of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	$ 111	$ (2,933)
Income tax expense (benefit)	(42)	1,121
Total reclassifications for the period, net of tax	69	(1,812)
Prior service cost
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	113	125
Actuarial losses
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	$ (2)	$ (3,058)

Asset Impairment - Summary of I

Asset Impairment - Summary of Impairments Recognized (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 1,460	$ 220,025
Central Basin Platform
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	1,096	187,043
Delaware Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	0	21,288
San Juan Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	0	7,519
Permian Basin unproved leasehold properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	364	4,135
San Juan Basin unproved leasehold properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 0	$ 40

Asset Impairment - Additional I

Asset Impairment - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 1,460	$ 220,025
Price curve, term	5 years
Increase (decrease) in carrying amount of properties, percent	3.00%
Oil
Impaired Long-Lived Assets Held and Used [Line Items]
Increase (decrease) in carrying amount of properties, percent		(5.00%)
Natural Gas
Impaired Long-Lived Assets Held and Used [Line Items]
Increase (decrease) in carrying amount of properties, percent		(4.00%)
Permian Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 1,100	$ 208,300
Permian Basin unproved leasehold properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	364	4,135
San Juan Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 0	$ 7,519

Acquisition and Disposition o63

Acquisition and Disposition of Properties - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Gas and Oil Acreage [Line Items]
Payment for unproved leasehold	$ 157.8	$ 7.6
Delaware Basin
Gas and Oil Acreage [Line Items]
Payment for unproved leasehold	111.9
Midland Basin
Gas and Oil Acreage [Line Items]
Payment for unproved leasehold	27.1
Mineral Purchases
Gas and Oil Acreage [Line Items]
Payment for unproved leasehold	18.8
Disposal group | Permian and San Juan Basin
Gas and Oil Acreage [Line Items]
Amount of consideration received	552
Held-for-sale | Permian and San Juan Basin
Gas and Oil Acreage [Line Items]
Proceeds from sale of oil and gas property and equipment	532.6
Purchase price adjustments	19
Transaction costs	5
Pre-tax gain on disposal	$ 246

Recently Issued Accounting St64

Recently Issued Accounting Standards - Narrative (Details) $ in Thousands	Mar. 31, 2017USD ($)
Additional Paid-in Capital | New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2016-09, Forfeiture Rate Component
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Decrease to retained earnings associated with our election to recognize forfeitures	$ 169