Energen (EGN) Inactive 10-K2 Mar 152014 FY Annual reportFinancial data

Company Profile

Document_and_Entity_Informatio

Document and Entity Information Document (USD $)	12 Months Ended
Document and Entity Information Document (USD $)	Dec. 31, 2014	Feb. 16, 2015	Jun. 30, 2014
Document and Entity [Abstract]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Entity Registrant Name	ENERGEN CORP
Entity Central Index Key	277595
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		72,991,974
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Public Float			$6,440,598,008

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Current Assets
Cash and cash equivalents	$1,852	$2,523
Accounts receivable, net of allowance for doubtful accounts of $688 and $696 at December 31, 2014 and 2013, respectively	157,678	136,334
Inventories	14,251	11,130
Assets held for sale	395,797	1,242,872
Deferred income taxes	0	21,250
Derivative instruments	322,337	17,463
Prepayments and other	27,445	9,989
Total current assets	919,360	1,441,561
Oil and gas properties, successful efforts method
Proved properties	6,903,514	6,695,400
Unproved properties	142,340	168,975
Less accumulated depreciation, depletion and amortization	1,893,106	1,776,802
Oil and gas properties, net	5,152,748	5,087,573
Other property and equipment, net	46,389	30,515
Total property, plant and equipment, net	5,199,137	5,118,088
Other postretirement assets	0	8,894
Noncurrent derivative instruments	0	5,439
Other assets	19,761	48,230
TOTAL ASSETS	6,138,258	6,622,212
Current Liabilities
Long-term debt due within one year	0	60,000
Notes payable to banks	0	489,000
Accounts payable	101,453	78,178
Accrued taxes	5,530	8,201
Accrued wages and benefits	46,162	27,036
Accrued capital costs	207,461	93,623
Revenue and royalty payable	72,047	51,519
Liabilities related to assets held for sale	24,230	831,570
Deferred income taxes	79,164	0
Derivative instruments	988	30,302
Other	23,288	21,796
Total current liabilities	560,323	1,691,225
Long-term debt	1,038,563	1,093,541
Asset retirement obligations	94,060	108,533
Pension and other postretirement liabilities	15,935	47,484
Deferred income taxes	1,000,486	807,614
Noncurrent derivative instruments	0	398
Other	14,287	15,398
Total liabilities	2,723,654	3,764,193
Commitments and Contingencies
TOTAL LIABILITIES AND SHAREHOLDERSâ€™ EQUITY	6,138,258	6,622,212
Shareholders' Equity
Preferred stock, cumulative, $0.01 par value	0	0
Common shareholdersâ€™ equity
Common stock, $0.01 par value; 150,000,000 shares authorized; 75,875,711 shares issued at December 31, 2014 and 75,574,156 shares issued at December 31, 2013	759	756
Premium on capital stock	564,438	523,711
Retained earnings	2,997,821	2,476,616
Accumulated other comprehensive income (loss), net of tax
Unrealized gain on hedges, net	0	13,362
Pension and postretirement plans	-22,870	-32,245
Interest rate swap	0	-1,184
Deferred compensation plan	2,862	3,259
Treasury stock, at cost; 2,980,598 shares and 2,967,999 shares at December 31, 2014 and 2013, respectively	-128,406	-126,256
Total shareholdersâ€™ equity	$3,414,604	$2,858,019

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$688	$696
Preferred stock, par value	$0.01	$0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Common stock, par value	$0.01	$0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	75,875,711	75,574,156
Treasury stock, shares	2,980,598	2,967,999

CONSOLIDATED_STATEMENTS_OF_INC

CONSOLIDATED STATEMENTS OF INCOME (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues
Oil, natural gas liquids and natural gas sales	$1,344,194	$1,256,317	$1,006,795
Gain (loss) on derivative instruments, net	335,019	-50,024	84,153
Total revenues	1,679,213	1,206,293	1,090,948
Operating Costs and Expenses
Oil, natural gas liquids and natural gas production	274,432	257,438	202,286
Production and ad valorem taxes	102,063	94,103	75,907
Depreciation, depletion and amortization	548,564	452,876	342,611
Asset impairment	416,801	13,906	6,304
Exploration	28,090	14,036	13,052
General and administrative	122,052	113,821	78,627
Accretion of discount on asset retirement obligations	7,608	6,995	6,339
Loss on sale of assets and other, net	2,642	981	1,718
Total operating costs and expenses	1,502,252	954,156	726,844
Operating Income	176,961	252,137	364,104
Other Income (Expense)
Interest expense	-37,771	-39,736	-47,565
Other income	1,181	3,803	1,645
Total other expense	-36,590	-35,933	-45,920
Income From Continuing Operations Before Income Taxes	140,371	216,204	318,184
Income tax expense	40,728	74,323	113,563
Income From Continuing Operations	99,643	141,881	204,621
Discontinued Operations, net of tax
Income from discontinued operations	29,292	59,079	48,941
Gain on disposal of discontinued operations, net	439,097	3,594	0
Income From Discontinued Operations	468,389	62,673	48,941
Net Income	$568,032	$204,554	$253,562
Diluted Earnings Per Average Common Share
Continuing operations (in dollars per share)	$1.36	$1.96	$2.83
Discontinued operations (in dollars per share)	$6.39	$0.86	$0.68
Net Income (in dollars per share)	$7.75	$2.82	$3.51
Basic Earnings Per Average Common Share
Continuing operations (in dollars per share)	$1.37	$1.96	$2.84
Discontinued operations (in dollars per share)	$6.42	$0.87	$0.68
Net Income (in dollars per share)	$7.79	$2.83	$3.52
Diluted Average Common Shares Outstanding (in shares)	73,274,631	72,470,622	72,316,214
Basic Average Common Shares Outstanding (in shares)	72,896,579	72,317,865	72,119,021

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Income	$568,032	$204,554	$253,562
Cash flow hedges:
Total cash flow hedges	-12,178	-32,018	35,864
Pension and postretirement plans:
Amortization of net benefit obligation at transition, net of tax of $8, $112 and $100, respectively	14	207	186
Amortization of prior service cost, net of tax of $87, $90 and $119, respectively	161	167	221
Amortization of net loss, net of tax of $7,676, $4,472 and $1,676, respectively	14,256	8,306	3,113
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Reclassification Adjustments, Net of Tax	-5,056	11,582	-17,443
Total pension and postretirement plans	9,375	20,262	-13,923
Comprehensive Income	565,229	192,798	275,503
Commodity Contract
Cash flow hedges:
Reclassification adjustment for derivative instruments, net of tax	37	-10,866	66,438
Reclassification adjustment for derivative instruments, net of tax	-13,399	-22,124	-29,359
Interest Rate Swap
Cash flow hedges:
Reclassification adjustment for derivative instruments, net of tax	-298	-148	-2,281
Reclassification adjustment for derivative instruments, net of tax	$1,482	$1,120	$1,066

CONSOLIDATED_STATEMENTS_OF_COM1

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current period change in fair value of interest rate swap, tax	$23	($6,660)	$40,720
Amortization of net obligation at transition, tax	8	112	100
Amortization of prior service cost, tax	87	90	119
Amortization of net loss, tax	7,676	4,472	1,676
Current period change in fair value of pension and postretirement plans, tax	-2,722	6,237	-9,393
Commodity Contract
Current period change in fair value of interest rate swap, tax	23	-6,660	40,720
Reclassification adjustment for derivative instruments, tax	-8,212	-13,560	-17,994
Interest Rate Swap
Current period change in fair value of interest rate swap, tax	-160	-80	-1,228
Reclassification adjustment for derivative instruments, tax	$798	$603	$574

CONSOLIDATED_STATEMENTS_OF_SHA

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $)	Total	Common Stock	Premium on Capital Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Deferred Compensation Plan	Treasury Stock
In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Premium on Capital Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Deferred Compensation Plan	Treasury Stock
Balance at Dec. 31, 2011	$2,432,163	$750	$485,720	$2,100,885	($30,252)	$3,511	($128,451)
Balance, shares at Dec. 31, 2011		75,007,412
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	253,562			253,562
Other comprehensive income	21,941				21,941
Purchase of treasury shares, net (5,459 shares in 2014, 14,766 shares in 2013, 32,768 shares in 2012)	-277						-277
Purchase and retirement of shares, shares		0
Shares issued for employee benefit plans, shares		60,348
Shares issued for employee benefit plans	2,061	1	2,060
Deferred compensation obligation	0					-737	737
Stock-based compensation	7,082		6,580				502
Tax benefit from employee stock plans	550		550
Cash dividends, per share - ($0.56 in 2012, $0.58 in 2013, $0.47 in 2014)	-40,392			-40,392
Balance at Dec. 31, 2012	2,676,690	751	494,910	2,314,055	-8,311	2,774	-127,489
Balance, shares at Dec. 31, 2012		75,067,760
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	204,554			204,554
Other comprehensive income	-11,756				-11,756
Purchase of treasury shares, net (5,459 shares in 2014, 14,766 shares in 2013, 32,768 shares in 2012)	-1,038						-1,038
Purchase and retirement of shares, shares		0
Shares issued for employee benefit plans, shares		506,396
Shares issued for employee benefit plans	18,795	5	18,790
Deferred compensation obligation	0					485	-485
Stock-based compensation	9,625		6,869				2,756
Tax benefit from employee stock plans	3,142		3,142
Cash dividends, per share - ($0.56 in 2012, $0.58 in 2013, $0.47 in 2014)	-41,993			-41,993
Balance at Dec. 31, 2013	2,858,019	756	523,711	2,476,616	-20,067	3,259	-126,256
Balance, shares at Dec. 31, 2013	75,574,156	75,574,156
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	568,032			568,032
Other comprehensive income	-2,803				-2,803
Purchase of treasury shares, net (5,459 shares in 2014, 14,766 shares in 2013, 32,768 shares in 2012)	-2,547						-2,547
Purchase and retirement of shares, shares		-226,839
Purchase and retirement of shares, value	-14,913	-2	-2,388	-12,523
Shares issued for employee benefit plans, shares		528,394
Shares issued for employee benefit plans	25,501	5	25,496
Deferred compensation obligation	0					-397	397
Stock-based compensation	11,713		11,713
Tax benefit from employee stock plans	5,906		5,906
Cash dividends, per share - ($0.56 in 2012, $0.58 in 2013, $0.47 in 2014)	-34,304			-34,304
Balance at Dec. 31, 2014	$3,414,604	$759	$564,438	$2,997,821	($22,870)	$2,862	($128,406)
Balance, shares at Dec. 31, 2014	75,875,711	75,875,711

Recovered_Sheet1

Consolidated Statements of Shareholders' Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Stockholders' Equity [Abstract]
Common stock, cash dividends per share	$0.47	$0.58	$0.56
Treasury Stock, Shares, Acquired	32,768	14,766	5,459

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Activities
Net Income	$568,032	$204,554	$253,562
Income from discontinued operations	-468,389	-62,673	-48,941
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, Depletion and Amortization	548,564	452,876	342,611
Asset impairment	416,801	13,906	6,304
Accretion of discount on asset retirement obligations	7,608	6,995	6,339
Deferred income taxes	302,890	118,600	128,171
Change in derivative fair value	-346,646	48,029	-41,819
(Gain) loss on sale of assets	55	-89	-529
Stock-based compensation expense	11,332	13,621	5,318
Exploration, including dry holes	9,325	2,102	10,453
Discontinued operations	91,510	109,318	85,065
Other, net	4,166	12,284	-714
Net change in:
Accounts receivable	4,812	23,785	4,111
Inventories	-3,121	10,817	-561
Accounts payable	18,695	-52,946	-14,038
Increase (Decrease) in Income Taxes Payable, Net of Income Taxes Receivable	-487,787	2,139	-6,679
Pension and other postretirement benefit contributions	-12,483	-5,677	-3,271
Other current assets and liabilities	40,119	29,736	10,355
Net cash provided by operating activities	705,483	927,377	735,737
Investing Activities
Additions to oil and natural gas properties	-1,264,059	-1,109,365	-1,107,911
Acquisitions, net of cash acquired	-70,730	-31,331	-139,563
Proceeds from sale of Alabama Gas Corporation and other assets	1,347,725	160,986	2,562
Purchase of short-term investments	-473,000	-310,000	0
Sale of short-term investments	473,000	310,000	0
Discontinued operations	-51,850	-73,341	-76,740
Other, net	0	-559	-530
Net cash used in investing activities	-38,914	-1,053,610	-1,322,182
Financing Activities
Payment of dividends on common stock	-34,304	-41,993	-40,392
Issuance of common stock	23,053	17,780	1,224
Purchase and retirement of shares	-14,913	0	0
Issuance of long-term debt	0	600,000	0
Reduction of long-term debt	-600,000	-350,000	-1,000
Payment of debt issuance costs	-10,901	-2,740	0
Net change in credit facility	-4,000	-77,000	566,000
Tax benefit on stock compensation	5,906	3,142	550
Discontinued operations	-35,113	-27,105	61,744
Other	0	0	-1,518
Net cash provided by (used in) financing activities	-670,272	122,084	586,608
Net change in cash and cash equivalents	-3,703	-4,149	163
Cash and cash equivalents at beginning of period	5,555	9,704	9,541
Cash and cash equivalents at end of period	1,852	5,555	9,704
Less cash and cash equivalents of discontinued operations at end of period	0	-3,032	-5,559
Cash and cash equivalents	$1,852	$2,523	$4,145

Organization_and_Basis_of_Pres

Organization and Basis of Presentation (Notes)	12 Months Ended
Organization and Basis of Presentation (Notes)	Dec. 31, 2014
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 and natural gas liquids-rich properties and natural gas in the Permian Basin in west Texas and the San Juan Basin in New Mexico and Colorado. Headquartered in Birmingham, Alabama, our operations are conducted through our subsidiary, Energen Resources Corporation (Energen Resources).

	Energen may, in the ordinary course of business, be involved in the sale of developed or undeveloped properties. All assets held for sale are reported at the lower of the carrying amount or estimated fair value. Certain of these held for sale properties also qualify as discontinued operations when the sale results in the elimination of operations and cash flows from company operations and when there will be no significant continuing involvement in the operations and cash flows of the sold component. The results of operations of these properties are reclassified and reported as discontinued operations for prior periods.

	Prior to September 2, 2014, Energen owned Alabama Gas Corporation (Alagasco), which was engaged in the purchase, distribution and sale of natural gas principally in central and north Alabama. On September 2, 2014, Energen completed the transaction to sell Alagasco to The Laclede Group, Inc. (Laclede) for $1.6 billion, less the assumption of $267 million in debt. The net pre-tax proceeds to Energen totaled approximately $1.32 billion resulting in a pre-tax gain of $726.5 million. This sale had an effective date of August 31, 2014. Energen used cash proceeds from the sale to reduce long-term and short-term indebtedness. During the second quarter of 2014, Energen classified Alagasco as held for sale and reflected the associated operating results in discontinued operations. See Note 15, Discontinued Operations and Held for Sale Properties, for further information regarding the sale of Alagasco.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES




	A. Principles of Consolidation

	The accompanying consolidated financial statements include Energen and its subsidiaries, principally Energen Resources, after elimination of all significant intercompany transactions in consolidation. In the opinion of management, our consolidated financial statements reflect all adjustments necessary to present fairly 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. In addition, and in connection with the sale of Alagasco, we have chosen to reformat our financial statements to reflect a presentation more closely aligned with our peers in the oil and natural gas industry. As part of the financial statement reformatting, certain reclassifications were made to conform prior periods’ financial statements to the current-year presentation. These reclassifications primarily included further detail under operating costs and expenses. We further reclassified all commodity hedges from oil and natural gas operating revenues to gain (loss) on derivative instruments, net, as follows:



	Years ended December 31, (in thousands)	2014			2013			2012
	Open non-cash mark-to-market gains (losses) on derivative instruments	$	315,445		$	(47,832	)	$	58,750

	Closed gains (losses) on derivative instruments	19,574			(2,192		)	25,403

	Gain (loss) on derivative instruments, net	$	335,019		$	(50,024	)	$	84,153













	We classified as discontinued operations interest on debt required to be extinguished, certain depreciation costs that ended at close of transaction, the related income tax impact of these items and the earnings of Alagasco. In addition, we reclassified from discontinued operations certain general and administrative (G&A) expenses, other income and the related tax impact from these items. The table below provides a detail of these items included in income (loss) from discontinued operations as follows:



	Years ended December 31, (in thousands)	2014			2013			2012
	Alagasco net income	$	40,646		$	57,399		$	49,402

	Depreciation, depletion and amortization	(408		)	(598		)	(572		)
	General and administrative	3,337			5,894			5,166

	Interest expense	(17,306		)	(13,815		)	(1,693		)
	Other income	(347		)	(1,342		)	(977		)
	Income tax expense (benefit)	5,567			3,728			(727		)

	Alagasco income from discontinued operations	31,489			51,266			50,599

	Energen income (loss) from discontinued operations	(2,197		)	7,813			(1,658		)

	Income from discontinued operations	$	29,292		$	59,079		$	48,941


	B. Oil and Natural Gas Operations

	Property and Related Depletion: Energen follows the successful efforts method of accounting for costs incurred in the exploration and development of oil, natural gas liquids and natural gas reserves. Lease acquisition costs are capitalized initially, and unproved properties are reviewed periodically to determine if there has been impairment of the carrying value, with any such impairment charged to exploration expense currently. All development costs are capitalized. 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, we continue 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) we are making sufficient progress assessing the reserves and the economic and operating viability of the project. Capitalized exploratory drilling costs are presented in unproved properties in the balance sheets. If the exploratory well is determined to be a dry well, the costs are charged to exploration expense. Other exploration costs, including geological and geophysical costs, are expensed as incurred. Depreciation, depletion and amortization expense is determined on a field-by-field basis using the units-of-production method based on proved reserves. Anticipated abandonment and restoration costs are capitalized and depreciated using the units-of-production method based on proved developed reserves.

	Operating Revenues: Energen utilizes the sales method of accounting to recognize oil, natural gas liquids and natural gas production revenue. Under the sales method, revenues are based on actual sales volumes of commodities sold to purchasers. Over-production liabilities are established only when it is estimated that a property’s over-produced volumes exceed the net share of remaining proved reserves for such property. Energen had no significant production imbalances at December 31, 2014 and 2013.

	Derivative Commodity Instruments: We periodically enter into derivative commodity instruments to hedge our exposure to price fluctuations on oil, natural gas and natural gas liquids production. Such instruments may include over-the-counter (OTC) swaps and basis swaps typically executed with investment and commercial banks and energy-trading firms. All derivative commodity instruments in a gain position are valued on a discounted basis incorporating an estimate of performance risk specific to each related counterparty. Derivative commodity instruments in a loss position are valued on a discounted basis incorporating an estimate of performance risk specific to Energen. All derivative transactions are included in operating activities on the consolidated statements of cash flows.

	Energen’s current policy is to not enter into agreements that require the posting of collateral. The majority of our counterparty agreements include provisions for net settlement of transactions payable on the same date and in the same currency. Most of the agreements include various contractual set-off rights, which may be exercised by the non-defaulting party in the event of an early termination due to a default.

	Prior to June 30, 2013, Energen used cash flow hedge accounting, where applicable, for its derivative transactions. The effective portion of the gain or loss on the derivative instrument was recognized in accumulated other comprehensive income as a component of shareholders’ equity and subsequently reclassified as gain (loss) on derivative instruments, net when the forecasted transaction affects earnings. The ineffective portion of a derivative’s change in fair value was required to be recognized immediately in gain (loss) on derivative instruments, net. All other derivative transactions not designated as cash flow hedge accounting 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.

	Effective March 31, 2013 and June 30, 2013, Energen dedesignated from cash flow hedge accounting 5,078 thousand barrels (MBbl) and 2,353 MBbl, respectively, of various NYMEX oil contracts with the Permian Basin due to lack of correlation. Gains and losses from inception of the hedge to the dedesignation date were frozen in accumulated other comprehensive income until the forecasted transactions actually occurred. Subsequent gains or losses are accounted for as mark-to-market transactions and recognized immediately through gain (loss) on derivative instruments, net.

Effective June 30, 2013, Energen discontinued the use of cash flow hedge accounting and dedesignated all remaining derivative commodity instruments that were previously designated as cash flow hedges. As a result of discontinuing hedge accounting, any gains or losses from inception of the hedge to June 30, 2013 were frozen in accumulated other comprehensive income until the forecasted transactions actually occurred. Any subsequent gains or losses are accounted for as mark-to-market and recognized immediately through gain (loss) on derivative instruments, net. As a result of Energen’s election to discontinue hedge accounting, all derivative transactions entered into subsequent to June 30, 2013 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.

Derivative transactions are pursuant to standing authorizations by the Board of Directors, which do not authorize speculative positions. Energen formally documents all relationships between hedging instruments and hedged items at the inception of the hedge, as well as its risk management objective and strategy for undertaking the hedge. This process includes specific identification of the hedging instrument and the nature of the risk being hedged. Our credit facility also limits our ability to enter into commodity hedges based on projected production volumes.

Asset Impairments: Oil and natural gas proved properties periodically are assessed for possible impairment on a field-by-field basis using the estimated undiscounted future cash flows. Impairment losses are recognized when the estimated undiscounted future cash flows are less than the current net book values of the properties in a field. Energen monitors its oil and natural gas properties as well as the market and business environments in which it operates and makes assessments about events that could result in potential impairment issues. Such potential events may include, but are not limited to, substantial commodity price declines, unanticipated increased operating costs, and lower than expected production performance. If a material event occurs, we make an estimate of undiscounted future cash flows to determine whether the asset is impaired. If the asset is impaired, Energen 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.

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 variables can, and often do, differ from the estimates and can have a positive or negative impact on our need for impairment or on the amount of impairment. In addition, further changes in the economic and business environment can impact Energen’s original and ongoing assessments of potential impairment.

Energen also may recognize impairments of capitalized costs for unproved properties. The greatest portion of these costs generally relate to the acquisition of leasehold. The costs are capitalized and periodically evaluated as to recoverability, based on changes brought about by exploration activities, changes in economic factors and potential shifts in business strategy employed by management. We consider a combination of geologic and economic factors to evaluate the need for impairment of these costs.

Long-Lived Assets and Discontinued Operations: Energen may, in the ordinary course of business, be involved in the sale of developed or undeveloped properties. All assets held for sale are reported at the lower of the carrying amount or estimated fair value. Certain of these held for sale properties also qualify as discontinued operations when the sale results in the elimination of operations and cash flows from company operations and when there will be no significant continuing involvement in the operations and cash flows of the sold component. The results of operations of these properties are reclassified and reported as discontinued operations for prior periods.

Acquisitions: Energen recognizes all acquisitions at fair value. Energen estimates the fair value of the assets acquired and liabilities assumed as of the acquisition date, the date on which Energen obtained control of the properties for all acquisitions that qualify as business combinations. The 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). Fair value measurements also utilize assumptions of market participants. Energen uses a discounted cash flow model and makes market assumptions as to future commodity prices, projections of estimated quantities of oil and natural gas reserves, expectations for timing and amount of future development and operating costs, projections of future rates of production, expected recovery rates and risk adjusted discount rates. These assumptions represent Level 3 inputs under the fair value hierarchy. Acquisition related costs are expensed as incurred in G&A expense on the consolidated income statements.

C. Inventory

Inventories consist primarily of tubular goods and other oilfield equipment used in our operations and are stated at the lower of cost or market value, on a weighted average cost basis.

D. Fair Value Measurements

The carrying values of cash and cash equivalents, accounts payable, accounts receivable (net of allowance), derivative commodity instruments, pension and postretirement plan assets and liabilities and other current assets and liabilities approximate fair value. 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 assumptions 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.

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 directly observable market prices are classified within Level 2 of the fair value hierarchy. These Level 2 fair values consist of swaps 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 basin specific, 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, we maintain communications with our counterparties and discuss pricing practices. Further, we corroborate the fair value of our transactions by comparison of market-based price sources.

Energen utilizes a discounted cash flow model in valuing its interest rate derivatives, which are comprised of interest rate swap agreements. The fair value attributable to Energen's interest rate derivative contracts is based on (i) the contracted notional amounts, (ii) active market-quoted LIBOR yield curves and (iii) the applicable credit-adjusted risk-free rate yield curve.

Pension and postretirement plan assets include cash and mutual funds. Plan assets were classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The determination and classification of fair value requires judgment and may affect the valuation of fair value assets and their placement within the fair value hierarchy. Level 1 and Level 2 fair values use market transactions and other market evidence whenever possible and consist primarily of equities, fixed income and mutual funds. Level 3 fair values used unobservable market prices primarily associated with certain alternative investments and a limited partnership in 2013 and 2012.




E. Income Taxes

Energen uses the liability method of accounting for income taxes. Under this method, a deferred tax asset or liability is recognized for the estimated future tax effects attributable to temporary differences between the financial statement basis and the tax basis of assets and liabilities as well as tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the period of the change. Energen and its subsidiaries file a consolidated federal income tax return. Consolidated federal income taxes are charged to appropriate subsidiaries using the separate return method.

F. Accounts Receivable and Allowance for Doubtful Accounts

Trade accounts receivable are recorded at the invoiced amounts and do not bear interest. The allowance for doubtful accounts is our best estimate of the amount of probable credit losses in the existing accounts receivable. Energen determines the allowance based on historical experience and in consideration of current market conditions. Account balances are charged against the allowance when it is anticipated the receivable will not be recovered.

G. Cash and Cash Equivalents

Cash and cash equivalents consist of cash in banks and investments readily convertible into cash, which have original maturities within three months at the date of acquisition. Cash equivalents are stated at cost, which approximates fair value.

H. Short-term Investments

All highly liquid financial instruments with maturities greater than three months and less than one year at the date of purchase are considered to be short-term investments. As of December 31, 2014 and 2013, Energen had no short-term investments.

I. Earnings Per Share (EPS)

Energen’s basic earnings per share amounts have been computed based on the weighted average number of common shares outstanding. Diluted earnings per share amounts reflect the assumed issuance of common shares for all potentially dilutive securities.

J. Stock-Based Compensation

Energen measures all share-based compensation awards at fair value at the date of grant and expenses the awards over the requisite vesting period. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if the actual forfeitures differ from those estimates. We recognize all stock-based compensation expense in the period of grant, subject to certain vesting requirements, for retirement eligible employees. Energen utilizes the long-form method of calculating the available pool of windfall tax benefit. For the years ended December 31, 2014, 2013 and 2012, we recognized an excess tax benefit of $5.9 million, $3.1 million and $0.6 million, respectively, related to our stock-based compensation.

K. Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and the reported amount of revenues and expenses during the reporting period. The major estimates and assumptions identified by management include, but are not limited to, physical quantities of proved oil and gas reserves, periodic assessments of oil and gas properties for impairment, Energen’s obligations under its employee pension and compensation plans, the valuation of derivative financial instruments, the allowance for doubtful accounts, tax contingency reserves, legal contingency reserves, asset retirement obligations and self insurance reserves. Due to the inherent uncertainty involved in making estimates, actual results reported in future periods may differ from the estimates.

L. Employee Benefit Plans

Energen has a defined benefit non-contributory qualified pension plan which covers substantially all employees. Pension benefits are based on years of service and final earnings. Energen also has nonqualified supplemental pension plans covering certain officers of Energen. In addition to providing pension benefits, Energen provides certain postretirement health care and life insurance benefits for all employees hired prior to January 1, 2010. These postretirement healthcare and life insurance benefits are available upon reaching normal retirement age while working for Energen. The projected unit credit actuarial method was used to determine the normal cost and actuarial liability.

Plan Separation: Effective April 30, 2014, Energen separated its defined benefit non-contributory pension plan and its postretirement healthcare and life insurance benefit plan into an Energen and an Alagasco plan reflecting the separation of assets and obligations in accordance with ERISA provisions. Energen remeasured the plans using current assumptions.

Plan Termination: 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 closes the plan to new entrants, effective November 1, 2014, and freezes benefit accruals effective December 31, 2014. Energen terminated the plan on January 31, 2015. We anticipate distributing benefits under the plan in late 2015 or early 2016 pending receipt of a determination letter from the IRS and completion of certain administrative actions.

Energen’s non-qualified supplemental retirement plans have also been amended to terminate effective December 31, 2014. Distributions under the plan are subject to certain payment restrictions under the Internal Revenue Code and Treasury regulations and payments to plan participants will be made in each of the first quarters of 2015 and 2016.

Measurement: For retirement plans and other postretirement plans, certain financial assumptions are used in determining Energen’s projected benefit obligation. These assumptions are examined periodically by Energen, and any required changes are reflected in the subsequent determination of projected benefit obligations.

Energen calculates periodic expense for the defined benefit pension plan and other postretirement benefit plans on an actuarial basis and the net funded status of benefit plans is recognized as an asset or liability in its statement of financial position with changes in the funded status recognized through comprehensive income. For the pension plan, the benefit obligation is the projected benefit obligation calculated on a plan termination basis assuming a distribution in one year; for other postretirement plans, the benefit obligation is the accumulated postretirement benefit obligation. Energen measures the funded status of its employee benefit plans as of the date of its year-end statement of financial position.

Discount Rate: For our defined benefit pension plan, we discounted the estimated termination liability using the one year spot rate of 0.70 percent. For our other postretirement plan, we selected a yield curve comprised of a broad base of Aa bonds with maturities between zero and thirty years. The discount rate for the postretirement plan was developed as the level equivalent rate that would produce the same present value as that using spot rates aligned with the projected benefit payments.

Long-Term Rate of Return: The assumed rate of return on assets is the weighted average of expected long-term asset assumptions. Energen considered past performance and current expectations for assets held by the plans as well as the expected long-term allocation of plan assets.

Other Significant Assumptions: The estimated weighted average rate of increase in the compensation level for pay related plans is another assumption used in calculation of the net periodic pension cost.

M. Environmental Costs

Environmental compliance costs, including ongoing maintenance, monitoring and similar costs, are expensed as incurred. Environmental remediation costs are accrued when remedial efforts are probable and the cost can be reasonably estimated.

LongTerm_Debt_and_Notes_Payabl

Long-Term Debt and Notes Payable	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Long-term Debt and Notes Payable	LONG-TERM DEBT AND NOTES PAYABLE




	Long-term debt consisted of the following:



	(in thousands)	December 31, 2014			December 31, 2013
	Credit facility	$	485,000		$	—

	7.40% Medium-term Notes, Series A, due July 24, 2017	2,000			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			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

	Senior Term Loans, (floating rate interest LIBOR plus 1.625%)	—			600,000

	Total	1,039,000			1,154,000

	Less amounts due within one year	—			60,000

	Less unamortized debt discount	437			459

	Total	$	1,038,563		$	1,093,541


	The aggregate maturities of Energen’s long-term debt as of December 31, 2014 are as follows:



	Years ending December 31, (in thousands)
	2015	2016	2017	2018	2019	Thereafter
	$—	$—	$19,000	$—	$485,000	$535,000

	In December 2013, the Company issued $600 million in Senior Term Loans with a floating interest rate due March 31, 2014 through December 17, 2017. In conjunction with the sale of Alagasco, the $600 million Senior Term Loans were repaid in September 2014.

	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 Facilities: On September 2, 2014, Energen entered into a $1.5 billion five-year syndicated secured credit facility with domestic and foreign lenders. The credit facility was amended to $2.0 billion on November 17, 2014. The credit facility has an initial borrowing base of $2.1 billion. This credit facility refinances and replaces the $1.25 billion five-year syndicated unsecured credit facility entered into on October 30, 2012. Energen’s obligations under the $2.0 billion 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 April 1, 2015.

	Under Energen’s 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 December 31, 2014.

	The following is a summary of information relating to Energen’s credit facilities:



	(in thousands)	December 31, 2014			December 31, 2013
Notes payable to banks	$	485,000		$	489,000

Available for borrowings	1,515,000			761,000

Total	$	2,000,000		$	1,250,000

Maximum amount outstanding at any month-end	$	750,000		$	859,000

Average daily amount outstanding	$	482,166		$	772,012

Weighted average interest rates based on:
Average daily amount outstanding	1.46		%	1.39		%
Amount outstanding at year-end	1.67		%	1.4		%

Energen’s total interest expense was $37.8 million, $39.7 million and $47.6 million for the years ended December 31, 2014, 2013 and 2012, respectively. Energen’s total interest expense for the years ended December 31, 2014, 2013 and 2012 included amortization of debt issuance costs of $5.7 million, $2.0 million and $2.4 million, respectively. In addition, Energen’s total interest expense for the years ended December 31, 2014, 2013 and 2012 included capitalized interest expense of $0.2 million, $0.2 million and $0.5 million, respectively. At December 31, 2014, Energen paid commitment fees on the unused portion of available credit facilities at a current annual rate of 30 basis points per annum. See Note 2, Summary of Significant Accounting Policies, for further information regarding interest on debt required to be extinguished, associated with the sale of Alagasco, which was classified to discontinued operations.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES




	The components of Energen’s income taxes consisted of the following:



	Years ended December 31, (in thousands)	2014			2013			2012
	Taxes estimated to be payable currently:
	Federal	$	161,576		$	23,342		$	16,295

	State	72,379			2,516			3,125

	Total current	233,955			25,858			19,420

	Taxes deferred:
	Federal	144,645			85,950			119,053

	State	(34,447		)	(2,300		)	5,346

	Total deferred	110,198			83,650			124,399

	Total income tax expense	$	344,153		$	109,508		$	143,819


	The components of Energen’s income taxes consisted of the following:



	Years ended December 31, (in thousands)	2014			2013			2012
	Income tax expense from continuing operations	$	40,728		$	74,323		$	113,563

	Income tax expense from discontinued operations	17,928			33,174			30,256

	Income tax expense from gain on disposal of discontinued operations	285,497			2,011			—

	Total income tax expense	$	344,153		$	109,508		$	143,819


	Temporary differences and carryforwards which gave rise to Energen’s deferred tax assets and liabilities were as follows:



	(in thousands)	December 31, 2014						December 31, 2013
		Current			Noncurrent			Current			Noncurrent
	Deferred tax assets:
	Minimum tax credit	$	—		$	46,338		$	—		$	—

	Allowance for doubtful accounts	244			—			251			—

	Insurance and other accruals	2,537			—			3,082			—

	Compensation accruals	11,355			—			12,925			—

	Pension and other costs	—			7,009			—			3,652

	Other comprehensive income	10,732			1,581			—			15,350

	Derivative instruments	—			—			10,769			—

	State net operating losses and other carryforwards	—			15,392			—			4,577

Other	665			—			235			—

Total deferred tax assets	25,533			70,320			27,262			23,579

Valuation allowance	(1,122		)	(2,467		)	(299		)	(2,674		)
Total deferred tax assets	24,411			67,853			26,963			20,905




Deferred tax liabilities:
Depreciation and basis differences	—			1,057,430			—			821,425

Derivative instruments	102,691			—			—			2,048

Other comprehensive income	—			—			5,540			—

Other	884			10,909			173			5,046

Total deferred tax liabilities	103,575			1,068,339			5,713			828,519

Net deferred tax assets (liabilities)	$	(79,164	)	$	(1,000,486	)	$	21,250		$	(807,614	)


Energen files a consolidated federal income tax return with all of its subsidiaries. As of December 31, 2014, the amount of minimum tax credit which can be carried forward indefinitely to reduce future regular tax liability is $46.3 million. Energen has a noncurrent deferred tax asset of $11.8 million relating to Energen Resources’ $254.6 million state net operating loss carryforward which will expire beginning in 2027. Energen Resources anticipates generating adequate future taxable income to fully realize this benefit. Energen has a full valuation allowance recorded against a noncurrent deferred tax asset of $3.6 million arising from certain state net operating loss and charitable contribution carryforwards. Energen intends to fully reserve this asset until it is determined that it is more likely than not that the asset can be realized through future taxable income in the respective state taxing jurisdictions. No other valuation allowance with respect to deferred taxes is deemed necessary as Energen anticipates generating adequate future taxable income to realize the benefits of all remaining deferred tax assets on the consolidated balance sheets.

Total income tax expense from continuing operations differed from the amount which would have been provided by applying the statutory federal income tax rate of 35 percent to earnings before taxes as illustrated below:



Years ended December 31, (in thousands)	2014			2013			2012
Income tax expense at statutory federal income tax rate	$	49,130		$	75,671		$	111,364

Increase (decrease) resulting from:
State income taxes, net of federal income tax benefit	93			1,461			2,423

Impact of state law changes	(121		)	(1,966		)	—

Impact of state deferred tax revaluation on San Juan properties	(8,382		)	—			—

401(k) stock dividend deduction	(232		)	(449		)	(514		)
Other, net	240			(394		)	290

Total income tax expense	$	40,728		$	74,323		$	113,563

Effective income tax rate (%)	29.01			34.38			35.69


Energen recognized an $8.4 million income tax benefit as a result of re-measuring its state deferred tax liabilities during the fourth quarter of 2014. This re-measurement reflected the state apportionment changes related to certain San Juan Basin properties designated as held for sale as of December 31, 2014.

















A reconciliation of Energen’s beginning and ending amount of unrecognized tax benefits is as follows:



(in thousands)
Balance as of December 31, 2011	$	10,593

Additions based on tax positions related to the current year	3,731

Additions for tax positions of prior years	269

Reductions for tax positions of prior years	(446		)
Lapse of statute of limitations	(1,592		)
Balance as of December 31, 2012	12,555

Additions based on tax positions related to the current year	4,546

Additions for tax positions of prior years	366

Reductions for tax positions of prior years	(46		)
Lapse of statute of limitations	(1,435		)
Balance as of December 31, 2013	15,986

Additions based on tax positions related to the current year	3,873

Additions for tax positions of prior years	19

Reductions for tax positions of prior years	(954		)
Lapse of statute of limitations	(1,394		)
Balance as of December 31, 2014	$	17,530


The amount of unrecognized tax benefits at December 31, 2014 that would favorably impact Energen’s effective tax rate, if recognized, is $7.6 million. Energen recognizes potential accrued interest and penalties related to unrecognized tax benefits in income tax expense. During the years ended December 31, 2014, 2013, and 2012, Energen recognized approximately $27,000 of expense, $15,000 of expense and $25,000 of income for interest (net of tax benefit) and penalties, respectively. Energen had approximately $0.2 million and $0.2 million for the payment of interest (net of tax benefit) and penalties accrued at December 31, 2014 and 2013, respectively.

Energen’s tax returns for years 2011-2013 remain open and subject to examination by the IRS and major state taxing jurisdictions. Accordingly, it is reasonably possible that significant changes to the reserve for uncertain tax benefits may occur as a result of various audits and the expiration of the statute of limitations. Although the timing and outcome of tax examinations is highly uncertain, Energen does not expect that the change in the unrecognized tax benefit within the next 12 months would have a material impact to the financial statements.

Employee_Benefit_Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2014
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS




	Plan Terminations: Effective April 30, 2014, Energen separated its defined benefit non-contributory pension plan and its postretirement healthcare and life insurance benefit plan into an Energen and an Alagasco plan reflecting the separation of assets and obligations in accordance with ERISA provisions. Energen remeasured the plans using current assumptions.

	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 closes the plan to new entrants, effective November 1, 2014, and freezes benefit accruals effective December 31, 2014. Energen terminated the plan on January 31, 2015. We anticipate distributing benefits under the plan in late 2015 or early 2016 pending receipt of a determination letter from the IRS and completion of certain administrative actions.

	Energen’s non-qualified supplemental retirement plans were amended to terminate effective December 31, 2014. Distributions under the plans are subject to certain payment restrictions under the Internal Revenue Code and Treasury regulations and payments to plan participants will be made in each of the first quarters of 2015 and 2016. In connection with the termination of these plans, Energen has also reclassified approximately $11.0 million as of December 31, 2014 of its investment in a Rabbi Trust from other long term assets to prepayments and other assets in the accompanying balance sheets to reflect its intent to utilize these assets to fund the estimated payments in the first quarter of 2015.

	Benefit Obligations: The following table sets forth the combined funded status of the defined qualified and nonqualified supplemental benefit plans along with the postretirement health care and life insurance benefit plans and their reconciliation with the related amounts in Energen’s consolidated financial statements. As Energen has frozen and plans to terminate the defined benefit pension plan, the projected pension benefit obligation as of December 31, 2014 represents the present value of the estimated cost of settling the plans benefit obligation. The amounts in the table below as of December, 31 2013 include both Energen and Alagasco, except for Alagasco plans which contain certain labor union agreements:



	As of December 31, (in thousands)	2014			2013			2014			2013
		Pension						Postretirement Benefits
	Accumulated benefit obligation	$	107,669		$	225,969

	Benefit obligation:
	Balance at beginning of period	$	266,294		$	293,075		$	33,224		$	46,901

	Service cost	8,329			13,293			262			1,125

	Interest cost	5,325			10,161			716			1,931

	Actuarial (gain) loss	9,078			(26,909		)	6,385			(13,311		)

	Curtailment gain	(8,496		)	(4,223		)	—			(1,255		)

	Transfer in connection with the sale of Alagasco	(124,783		)	—			(28,648		)	—

	Termination benefit charge	2,477			—			—			—

	Retiree drug subsidy program	—			—			48			124

	Benefits paid	(50,555		)	(19,103		)	(860		)	(2,291		)
	Balance at end of period	$	107,669		$	266,294		$	11,127		$	33,224

	Plan assets:
	Fair value of plan assets at beginning of period	$	193,457		$	182,796		$	55,459		$	48,194

	Actual return (loss) on plan assets	5,359			19,595			(331		)	8,072

	Employer contributions	19,164			10,169			21			1,484

	Transfer in connection with the sale of Alagasco	(99,883		)	—			(43,596		)	—

	Benefits paid	(50,555		)	(19,103		)	(860		)	(2,291		)
	Fair value of plan assets at end of period	$	67,542		$	193,457		$	10,693		$	55,459


	Funded status of plans	$	(40,127	)	$	(72,837	)	$	(434	)	$	22,235



	Noncurrent assets	$	—		$	—		$	—		$	8,894

	Noncurrent assets in assets held for sale	—			—			—			13,341

	Current liabilities	(24,626		)	(6,145		)	—			—

	Noncurrent liabilities	(15,501		)	(47,485		)	(434		)	—

Noncurrent liabilities in liabilities related to assets held for sale	—			(19,207		)	—			—

Net asset (liability) recognized	$	(40,127	)	$	(72,837	)	$	(434	)	$	22,235

Amounts recognized to accumulated other comprehensive income:
Prior service costs, net of taxes	$	—		$	323		$	—		$	—

Net actuarial (gain) loss, net of taxes	22,246			37,479			624			(5,584		)

Transition obligation, net of taxes	—			—			—			27

Total accumulated other comprehensive income (loss)	$	22,246		$	37,802		$	624		$	(5,557	)





Other investment assets designated for payment of the nonqualified supplemental retirement plans were as follows:



	December 31, 2014
(in thousands)	Level 1			Level 2			Total
Fixed income	$	—		$	4,255		$	4,255

Cash and cash equivalents	9,929			—			9,929

Total	$	9,929		$	4,255		$	14,184




	December 31, 2013
(in thousands)	Level 1			Level 2			Total
Insurance contracts	$	—		$	14,805		$	14,805

United States equities	5,579			—			5,579

Global equities	2,338			—			2,338

Fixed income	—			11,039			11,039

Total	$	7,917		$	25,844		$	33,761


While intended for payment of the nonqualified supplemental retirement plan benefits, these assets remain subject to the claims of Energen’s creditors and are not recognized in the funded status of the plan. These assets are recorded at fair value and included in prepayments and other and other assets in the consolidated balance sheets.

The following is a reconciliation of insurance contracts in Level 3 of the fair value hierarchy:



Years ended December 31, (in thousands)	2013			2012
Balance at beginning of period	$	5,600		$	5,332

Unrealized gains relating to instruments held at the reporting date	—			268

Transfer out of Level 3	(5,600		)	—

Balance at end of period	$	—		$	5,600


Transfer of Insurance Contracts: For the year ended December 31, 2014, there were no significant transfers in or out of Levels 1, 2, or 3. During 2013, Energen determined that its insurance contracts meet the requirements to be categorized as a Level 2 fair value measurement. The insurance contracts consist of multiple contracts with two insurance companies and are accounted for at fair value at the contracts’ cash surrender values.



















The components of net periodic benefit cost from continuing operations were as follows:



Years ended December 31, (in thousands)	2014			2013			2012
Pension Plans
Components of net periodic benefit cost:
Service cost	$	6,808		$	5,196		$	4,023

Interest cost	4,498			4,496			4,296

Expected long-term return on assets	(4,386		)	(5,225		)	(5,134		)
Prior service cost amortization	202			246			209

Actuarial loss amortization	4,995			6,919			3,945

Termination benefit charge	2,477			—			—

Settlement charge	4,082			161			—

Curtailment expense (gain)	254			(4		)	—

Net periodic expense	$	18,930		$	11,789		$	7,339

Postretirement Benefit Plans
Components of net periodic benefit cost:
Service cost	$	253		$	386		$	454

Interest cost	661			645			810

Expected long-term return on assets	(1,122		)	(787		)	(741		)
Actuarial gain amortization	(653		)	(28		)	—

Transition obligation amortization	44			229			248

Net periodic (income) expense	$	(817	)	$	445		$	771


Other changes in plan assets and projected benefit obligations recognized in other comprehensive income were as follows:



Years ended December 31, (in thousands)	2014			2013			2012
Pension Plans
Net actuarial (gain) loss experienced during the year	$	10,495		$	(14,138	)	$	28,748

Net actuarial loss recognized as expense	(25,433		)	(8,934		)	(4,908		)
Prior service cost recognized as expense	(246		)	(311		)	(340		)
Curtailment loss	(8,749		)	—			—

Total recognized in other comprehensive income (loss)	(23,933		)	(23,383		)	23,500

Postretirement Benefit Plans
Net actuarial (gain) loss experienced during the year	$	7,649		$	(8,057	)	$	(1,787	)

Net actuarial gain recognized as expense	1,908			550			—

Transition obligation recognized as expense	(48		)	(283		)	(294		)
Total recognized in other comprehensive income (loss)	$	9,509		$	(7,790	)	$	(2,081	)


In the first quarter of 2014, Energen incurred settlement charges of $6.9 million for the payment of lump sums from the qualified defined benefit pension plans of which $3.7 million is included in discontinued operations. Also in the first quarter of 2014, Energen incurred a settlement charge of $0.4 million for the payment of lump sums from the non-qualified supplemental retirement plans. In the second quarter of 2014, Energen incurred settlement charges of $0.4 million for the payment of lump sums from the qualified defined benefit pension plans. In the third quarter of 2014, Energen incurred a settlement charge of $26,000 for the payment of lump sums from the non-qualified supplemental retirement plans. Also in the third quarter of 2014, Energen incurred settlement charges of $0.3 million for the payment of lump sums from the qualified defined benefit pension plan. In the fourth quarter of 2014, Energen incurred a settlement charge of $1.8 million for the payment of lump sums from the non-qualified supplemental retirement plans which is included in discontinued operations. Also in the fourth quarter of 2014, Energen incurred settlement charges of $39,000 for the payment of lump sums from the qualified defined benefit pension plan. In the fourth quarter of 2014, Energen recognized a termination benefit charge of $2.5 million to provide for early retirement of certain non-highly compensated employees. In conjunction with the sale of Alagasco, Energen recognized a curtailment loss of $0.3 million in the fourth quarter of 2014.

In the first quarter of 2013, Energen incurred a settlement charge of $0.5 million for the payment of lump sums from the nonqualified supplemental retirement plans, of which $0.1 million was expensed and $0.4 million was recognized as a regulatory asset at Alagasco. In the third quarter of 2013, Energen incurred a settlement charge of $64,000 for the payment of lump sums from the nonqualified supplemental retirement plans, of which $18,000 was expensed and $46,000 was recognized as a regulatory asset at Alagasco. In conjunction with the sale of its Black Warrior Basin coalbed methane properties in Alabama, Energen recognized a curtailment gain of $1.2 million in the fourth quarter of 2013.

Estimated amounts to be amortized from accumulated other comprehensive income into pension cost during 2015 are included in the table below. In addition, the Company anticipates recognizing the remaining amounts from accumulated other comprehensive income on the date of distribution of pension plan benefits.



(in thousands)
Amortization of net actuarial loss	$	841


Energen has a long-term disability plan covering most employees. Energen had expense of $0.2 million for each of the years ended December 31, 2014, 2013 and 2012.

Assumptions: The weighted average rate assumptions to determine net periodic benefit costs were as follows:



Years ended December 31,	2014		2013		2012
Pension Plans
Discount rate	3.66	%	3.63	%	4.52	%
Expected long-term return on plan assets	7	%	7	%	7	%
Rate of compensation increase for pay-related plans	3.63	%	3.71	%	3.59	%
Postretirement Benefit Plans
Discount rate	4.88	%	4.36	%	4.95	%
Expected long-term return on plan assets	7	%	7	%	7	%
Rate of compensation increase	3.6	%	3.7	%	3.55	%

The pension benefit obligation as of December 31, 2014 represents the present value of the estimated cost of settling the benefit obligation of the plan. For our defined benefit pension plan, we discounted the estimated termination liability using the one year spot rate of 0.70 percent. The discount rate shown below represents the weighted average for both the defined qualified and nonqualified supplemental benefit plans. As the plans were frozen as of December 31, 2014, the rate of compensation increase no longer applies for any of the plans. The weighted average assumptions used to determine the benefit obligations at the measurement date were as follows:



Years ended December 31,	2014		2013
Pension Plans
Discount rate	0.96	%	4.29	%
Rate of compensation increase for pay-related plans	—	%	3.63	%
Postretirement Benefit Plans
Discount rate	4.25	%	4.95	%
Rate of compensation increase for pay-related plans	—	%	3.6	%



The assumed post-65 health care cost trend rates used to determine the postretirement benefit obligation at the measurement date were as follows:



As of December 31,	2014		2013
Health care cost trend rate assumed for next year	7.25	%	6.5	%
Rate to which the cost trend rate is assumed to decline	5	%	5	%
Year that rate reaches ultimate rate	2021		2020


Health care costs trend rates will not have a material impact to the accumulated postretirement benefit obligation due to the separation of assets and obligations of the postretirement healthcare and life insurance benefit plan into an Energen and an Alagasco plan. Employees remaining at Energen will receive a fixed postretirement benefit.

Investment Strategy: Due to the plan termination of our defined benefit plans, we have transitioned our investment strategy to reduce risk. We liquidated our equity and debt securities and have invested fully in cash and cash equivalents at year-end. We expect to hold these funds along with any additional contributions in cash until the benefits are fully distributed.

For our postretirement benefit plan assets, we continue to employ a total return investment approach whereby a mix of equities and fixed income investments are used to maximize the long-term return of plan assets with a prudent level of risk. Risk tolerance is established through consideration of plan liabilities, plan funded status, corporate financial condition and market conditions.

Energen seeks to maintain an appropriate level of diversification to minimize the risk of large losses in a single asset class. Accordingly, plan assets for the postretirement health care and life insurance benefit plan do not have a concentration of assets in a single entity, industry, commodity or class of investment fund.

The Company’s weighted average plan asset allocations by asset category were as follows:



	Pension						Postretirement Benefits
As of December 31,	Target		2014		2013		Target		2014		2013
Asset category:
Equity securities	—	%	—	%	34	%	60	%	60	%	61	%
Debt securities	—	%	—	%	28	%	40	%	40	%	39	%
Other	100	%	100	%	38	%	—	%	—	%	—	%
Total	100	%	100	%	100	%	100	%	100	%	100	%

Equity securities for pension and postretirement benefits do not include the Company’s common stock.

Plan assets included in the funded status of the pension plans were as follows:


	31-Dec-14
(in thousands)	Level 1			Level 2			Total
Cash and cash equivalents	$	67,542		$	—		$	67,542

Total	$	67,542		$	—		$	67,542




	December 31, 2013
(in thousands)	Level 1			Level 2			Total
United States equities	$	34,117		$	—		$	34,117

Global equities	20,144			8,636			28,780

Fixed income	—			50,777			50,777

Alternative investments	—			37,292			37,292

Cash and cash equivalents	5,970			36,521			42,491

Total	$	60,231		$	133,226		$	193,457


Pension plan assets at December 31, 2013 include the assets of Alagasco. Energen had no Level 3 pension plan assets. United States equities consist of mutual and commingled funds with varying strategies. Such strategies include stock investments across market capitalizations and investment styles. Global equities consist of mutual funds and a limited partnership that invest in United States and non-United States securities broadly diversified across mostly developed markets but with some tactical exposure to emerging markets. Fixed income securities consist of mutual funds and separate accounts. Fixed income securities are well diversified with allocations to investment grade and non-investment grade issues and issues that provide both intermediate and longer duration exposure. Alternative investments consist of limited partnerships and commingled and mutual funds with varying investment strategies. Alternative investments are meant to serve as a risk reducer at the total portfolio level as they provide asset class exposures not found elsewhere in the portfolio.

The following is a reconciliation of plan assets in Level 3 of the fair value hierarchy:



Years ended December 31, (in thousands)	2013			2012
Balance at beginning of period	$	14,500		$	17,399

Unrealized gains (losses)	—			992

Unrealized gains relating to instruments held at the reporting date	—			242

Settlements	—			(4,948		)

Purchases	—			815

Transfer out of Level 3	(14,500		)	—

Balance at end of period	$	—		$	14,500


Transfer of Alternative Investments: For the year ended December 31, 2014 there were no significant transfers in or out of Levels 1, 2, or 3. During 2013, Energen determined that its alternative investments meet the requirements to be categorized as Level 2 fair value measurement. The alternative investments consist of three investments that are measured at net asset value. Net asset value per share serves as an estimate for the fair value of an investment as long as certain requirements are met.

Plan assets included in the funded status of the postretirement benefit plans were as follows:



	December 31, 2014
(in thousands)	Level 1			Level 2			Total
United States equities	$	4,715		$	—		$	4,715

Global equities	1,711			—			1,711

Fixed income	—			4,267			4,267

Total	$	6,426		$	4,267		$	10,693




	December 31, 2013
(in thousands)	Level 1			Level 2			Total
United States equities	$	24,152		$	—		$	24,152

Global equities	9,563			—			9,563

Fixed income	—			21,744			21,744

Total	$	33,715		$	21,744		$	55,459


Postretirement benefit plan assets at December 31, 2013 include the assets of Alagasco. Energen had no Level 3 postretirement benefit plan assets. United States equities consists of mutual funds with varying strategies. These funds invest largely in medium to large capitalized companies with exposure blending growth, market-oriented and value styles. Additional fund investments include small capitalization companies, and certain of these funds utilize tax-sensitive management approaches. Global equities are mutual funds that invest in non-United States securities broadly diversified across most developed markets with exposure blending growth, market-oriented and value styles. Fixed income securities are high-quality short-duration securities including investment-grade market sectors with tactical investments in non-investment grade sectors.

Cash Flows: During 2015, Energen anticipates an additional contribution of $13.7 million in order to complete the distribution of plan assets related to the plan termination. The Company expects to make benefit payments, which will be funded by the Rabbi Trust, of approximately $11.0 million during 2015 with respect to the termination of the nonqualified supplemental retirement plans.

Due to restructuring of our plans, Energen no longer qualifies for benefits related to the Medicare Prescription Drug, Improvement and Modernization Act of 2003. The following benefit payments, which reflect expected future service, as appropriate, are anticipated to be paid as follows:



(in thousands)	Pension Benefits	Postretirement Benefits
2015	$92,711	$324
2016	$14,601	$397
2017	$113	$472
2018	$110	$541
2019	$107	$583
2020-2024	$484	$3,266

Common_Stock_Plans

Common Stock Plans	12 Months Ended
	Dec. 31, 2014
Share-based Compensation [Abstract]
Common Stock Plans	COMMON STOCK PLANS




	Energen Employee Savings Plan (ESP): In October 2014, Energen’s Board of Directors amended and restated the ESP to make certain benefit design changes effective January 1, 2015. The benefit design changes include an increase in the percentage of Energen match and other contributions. A majority of our employees are eligible to participate in the ESP by electing to contribute a portion of their compensation to the ESP. Energen may match a percentage of the contributions and make these contributions in Energen common stock or in funds for the purchase of Energen common stock. Employees may diversify 100 percent of their ESP Energen stock account into other ESP investment options. The ESP also contains employer supplemental contributions. Effective January 1, 2015, the Company match will no longer be contributed in Energen common stock. Expense associated with Energen contributions to the ESP was $3.7 million, $3.7 million and $3.3 million for the years ended December 31, 2014, 2013 and 2012, respectively.

	Stock Incentive Plan: The Stock Incentive Plan provided for the grant of incentive stock options and non-qualified stock options to officers and key employees. The Stock Incentive Plan also provided for the grant of performance share awards and restricted stock units. Energen has typically funded options, restricted stock obligations and performance share obligations through original issue shares and restricted stock through treasury shares. Under the Stock Incentive Plan, 8,600,000 shares of Energen common stock were reserved for issuance with 2,635,544 remaining for issuance as of December 31, 2014.





















	Performance Share Awards: The Stock Incentive Plan provided for the grant of performance share awards, with each unit equal to the market value of one share of common stock, to eligible employees based on predetermined Energen performance criteria at the end of an award period. The Stock Incentive Plan provided that payment of earned performance share awards be made in the form of Energen common stock.

	No performance share awards were granted in 2012. A summary of performance share award activity as of December 31, 2014, and transactions during the years ended December 31, 2014 and 2013 is presented below:



		Stock Incentive Plan
		Shares		Weighted
				Average Price

	Nonvested at December 31, 2012	—		$	—

	Granted (two-year vesting period)	86,221		61.14

	Granted (three-year vesting period)	82,606		62.96

	Forfeited	(8,008	)	60.03

	Nonvested at December 31, 2013	160,819		62.13

	Granted (two-year vesting period)	937		131.56

	Granted (three-year vesting period)	65,309		93.49

	Vested and paid	(14,097	)	70.06

	Nonvested at December 31, 2014	212,968		$	71.53


	Energen recorded expense of $6.2 million and $3.8 million for the years ended December 31, 2014 and 2013, respectively, for performance share awards with a related deferred income tax benefit of $2.3 million and $1.4 million. During the year ended December 31, 2012, Energen recorded no expense for performance share awards. As of December 31, 2014, there was $5.6 million of total unrecognized compensation cost related to performance share awards. These awards have a remaining weighted average requisite service period of 1.45 years.




























Stock Options: The Stock Incentive Plan provided for the grant of incentive stock options, non-qualified stock options, or a combination thereof to officers and key employees. Options granted under the Stock Incentive Plan provided for the purchase of Energen common stock at not less than the fair market value on the date the option was granted. The sale or transfer of the shares is limited during certain periods. All outstanding options are incentive or non-qualified, vest within three years from date of grant and expire 10 years from the grant date.

A summary of stock option activity as of December 31, 2014, and transactions during the years ended December 31, 2014, 2013 and 2012 are presented below:



	Stock Incentive Plan
	Shares		Weighted Average Exercise Price


Outstanding at December 31, 2011	1,338,241		$	44.77

Granted	371,040		54.11

Exercised	(58,471	)	24.55

Forfeited	(2,335	)	46.45

Outstanding at December 31, 2012	1,648,475		47.58

Granted	137,762		49.22

Exercised	(590,119	)	40.92

Forfeited	(5,074	)	51.85

Outstanding at December 31, 2013	1,191,044		51.06

Granted	110,307		72.55

Exercised	(544,280	)	50.09

Outstanding at December 31, 2014	757,071		$	54.88

Exercisable at December 31, 2012	987,733		$	43.75

Exercisable at December 31, 2013	713,445		$	49.8

Exercisable at December 31, 2014	454,938		$	51.88

Remaining reserved for issuance at December 31, 2014	2,635,544		—


Energen uses the Black-Scholes pricing model to calculate the fair values of the options awarded. For purposes of this valuation the following assumptions were used to derive the fair values:



Grant date	4/15/14	1/22/14	10/15/13	1/24/13		1/25/12
Awards granted	2,439	107,868	3,686	134,076		371,040

Fair market value of stock option at grant	$32.22	$27.57	$30.53	$16.66		$18.79
Expected life of award	5.8 years	5.8 years	5.8 years	5.8 years		5.8 years

Risk-free interest rate	1.93%	2.06%	1.79%	1.01	%	1.07	%
Annualized volatility rate	40.70%	40.70%	40.60%	40.3	%	39.6	%
Dividend yield	0.20%	0.80%	0.70%	1.2	%	1	%

Energen recorded stock option expense of $2.9 million, $3.4 million and $6.2 million during the years ended December 31, 2014, 2013 and 2012, respectively, with a related deferred tax benefit of $1.1 million, $1.3 million and $2.3 million, respectively.

The total intrinsic value of stock options exercised during the year ended December 31, 2014, was $18.5 million. During the year ended December 31, 2014, Energen received cash of $23.1 million from the exercise of stock options. Total intrinsic value for outstanding options as of December 31, 2014, was $7.8 million and $5.4 million for exercisable options. The fair value of options vested for the year ended December 31, 2014 was $5.0 million. As of December 31, 2014, there was $0.5 million of unrecognized compensation cost related to outstanding nonvested stock options.
The following table summarizes options outstanding as of December 31, 2014:



Stock Incentive Plan
Range of Exercise Prices	Shares	Weighted Average Remaining Contractual Life
$46.45	25,470	2.00 years
$60.56	48,560	3.00 years
$29.79	35,161	4.00 years
$46.69	26,481	5.00 years
$54.99	111,487	6.00 years
$54.11	271,848	7.00 years
$48.36	124,071	8.00 years
$80.48	3,686	8.79 years
$72.39	107,868	9.00 years
$79.63	2,439	9.00 years
$29.79-$80.48	757,071	6.68 years

The weighted average remaining contractual life of currently exercisable stock options is 5.79 years as of December 31, 2014.

Restricted Stock: In addition, the Stock Incentive Plan provided for the grant of restricted stock units which have been valued based on the quoted market price of Energen’s common stock at the date of grant. Restricted stock units vest within three years from grant date. A summary of restricted stock unit activity as of December 31, 2014, and transactions during the years ended December 31, 2014, 2013 and 2012 is presented below:



	Stock Incentive Plan
	Shares		Weighted Average Price
Nonvested at December 31, 2011	9,275		$	42.99

Granted	11,115		45.24

Vested	(9,275	)	42.97

Nonvested at December 31, 2012	11,115		45.24

Granted	52,650		52.34

Forfeited	(1,247	)	48.36

Nonvested at December 31, 2013	62,518		51.16

Granted	48,904		71.91

Vested	(11,848	)	65.94

Nonvested at December 31, 2014	99,574		$	59.6


Energen recorded expense of $3.2 million, $1.9 million and $0.1 million for the years ended December 31, 2014, 2013 and 2012, respectively, related to restricted stock units, with a related deferred income tax benefit of $1.2 million, $0.7 million and $23,000, respectively. As of December 31, 2014, there was $1.3 million of total unrecognized compensation cost related to nonvested restricted stock awards recorded in premium on capital stock. These awards have a remaining requisite service period of 1.46 years.

Stock Appreciation Rights Plan: The Energen Stock Appreciation Rights Plan provided for the payment of cash incentives measured by the long-term appreciation of Energen common stock. Officers of Energen are not eligible to participate in this Plan. These awards are liability awards which settle in cash and are remeasured each reporting period until settlement. These awards have a three year requisite service period.

A summary of stock appreciation rights activity as of December 31, 2014, and transactions during the years ended December 31, 2014, 2013 and 2012 are presented below:



	Stock Appreciation Rights Plan
	Shares		Weighted Average Exercise Price


Outstanding at December 31, 2011	777,218		$	42

Exercised/forfeited	(124,188	)	30.9

Outstanding at December 31, 2012	653,030		44.14

Granted	88,000		48.36

Exercised/forfeited	(363,653	)	39.66

Outstanding at December 31, 2013	377,377		49.48

Granted	62,749		72.39

Exercised/forfeited	(164,976	)	52.37

Outstanding at December 31, 2014	275,150		$	52.96


Energen issued the following awards with stock appreciation rights. Energen uses the Black-Scholes pricing model to calculate the fair values of the options awarded. On December 19, 2013, we modified certain stock appreciation rights subsequent to the original grant date. For purposes of this valuation the following assumptions were used to derive the fair values as of December 31, 2014:



Grant date	1/22/14	1/24/13	1/24/13	1/26/11	1/26/11
			(modified)		(modified)
Awards granted	62,749	87,069	931	182,199	7,785
Fair market value of award	$18.63	$25.93	$20.14	$19.15	$16.27
Expected life of award	5.56 years	4.57 years	2.0 years	3.04 years	2.0 years
Risk-free interest rate	1.77%	1.57%	0.65%	1.12%	0.65%
Annualized volatility rate	33.40%	33.40%	33.40%	33.40%	33.40%
Dividend yield	0.13%	0.13%	0.13%	0.13%	0.13%



Grant date	1/27/10	2/13-16/2009	1/28/09	2/4/08	2/1/07
Awards granted	171,749	3,292	305,257	67,093	85,906
Fair market value of award	$22.50	$33.23	$34.66	$10.57	$19.25
Expected life of award	2.54 years	2.04 years	2.04 years	1.55 years	1.04 years
Risk-free interest rate	0.90%	0.67%	0.67%	0.45%	0.26%
Annualized volatility rate	33.40%	33.40%	33.40%	33.40%	33.40%
Dividend yield	0.13%	0.13%	0.13%	0.13%	0.13%

Income associated with stock appreciation rights of $0.4 million and $0.9 million was recorded for the years ended December 31, 2014 and 2012. Expense associated with stock appreciation rights of $9.9 million was recorded for the year ended 2013. During the year ended December 31, 2014, the total intrinsic value of stock appreciation rights exercised was $4.4 million. During the year ended December 31, 2014, Energen paid $3.0 million in settlement of stock appreciation rights.

Petrotech Incentive Plan: The Energen Resources’ Petrotech Incentive Plan provided for the grant of stock equivalent units which may include market conditions. Officers of Energen are not eligible to participate in this Plan. These awards are liability awards which are remeasured each reporting period and settle in cash at completion of the vesting period. Stock equivalent units with service conditions were valued based on Energen’s stock price at the end of the period adjusted to remove the present value of future dividends.
A summary of Petrotech unit activity as of December 31, 2014, and transactions during the years ended December 31, 2014, 2013 and 2012 are presented below:



		Petrotech Incentive Plan
		Shares


Outstanding at December 31, 2011		11,061
Granted (three-year vesting period)		102,349

Granted (two-year vesting period)		3,768

Granted (18 month vesting period)		40,822

Paid		(3,281	)
Forfeited		(13,476	)
Outstanding at December 31, 2012		141,243

Granted (three-year vesting period)		92,418

Granted (17 month vesting period)		2,952

Paid		(36,792	)
Forfeited		(26,529	)
Outstanding at December 31, 2013		173,292

Granted		76,084
Paid		(4,431	)
Forfeited		(31,075	)
Outstanding at December 31, 2014		213,870


None of the awards issued included a market condition. Energen Resources recognized expense of $4.5 million, $6.2 million and $2.6 million during 2014, 2013 and 2012, respectively, related to these units.

1997 Deferred Compensation Plan: The 1997 Deferred Compensation Plan allowed officers and non-employee directors to defer certain compensation. Amounts deferred by a participant under the 1997 Deferred Compensation Plan are credited to accounts maintained for a participant in either a stock account or an investment account. The stock account tracks the performance of Energen’s common stock, including reinvestment of dividends. The investment account tracks the performance of certain mutual funds. Energen has funded, and presently plans to continue funding, a trust in a manner that generally tracks participants’ accounts under the 1997 Deferred Compensation Plan. While intended for payment of benefits under the 1997 Deferred Compensation Plan, the trust’s assets remain subject to the claims of our creditors. Amounts earned under the 1997 Deferred Compensation Plan and invested in Energen common stock held by the trust have been recorded as treasury stock, along with the related deferred compensation obligation in the consolidated statements of shareholders’ equity. As of December 31, 2014 there were 691,222 shares reserved for issuance from the 1997 Deferred Compensation Plan.

1992 Energen Corporation Directors Stock Plan: In 1992 Energen adopted the Energen Corporation Directors Stock Plan to pay a portion of the compensation of its non-employee directors in shares of Energen common stock. Under the Plan, 10,360 shares, 13,500 shares and 11,120 shares were awarded during the years ended December 31, 2014, 2013 and 2012, respectively, leaving 127,924 shares reserved for issuance as of December 31, 2014.

Stock Repurchase Authorization: By resolution adopted October 22, 2014, the Board of Directors authorized Energen to repurchase up to 3,600,000 shares of Energen common stock, replacing and superseding its prior stock repurchase authorizations. The resolution does not have an expiration date and does not limit Energen’s authorization to acquire shares in connection with tax withholdings and payment of exercise price on stock compensation plans. For the year ended December 31, 2014, Energen repurchased and retired 226,839 shares for $14.9 million pursuant to our repurchase authorization. There were no shares repurchased pursuant to its repurchase authorization for the years ended December 31, 2013 and 2012. As of December 31, 2014, a total of 3,373,161 shares remain authorized for future repurchase. Energen also from time to time acquires shares in connection with participant elections under Energen’s stock compensation plans. For the years ended December 31, 2014, 2013 and 2012, Energen acquired 32,768 shares, 14,766 shares and 5,459 shares, respectively, in connection with its stock compensation plans.

Derivative_Commodity_Instrumen

Derivative Commodity Instruments	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Commodity Instruments	DERIVATIVE COMMODITY INSTRUMENTS




	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)	31-Dec-14
											Gross Amounts Not Offset in the Balance Sheets
		Gross Amounts Recognized at Fair Value			Gross Amounts Offset in the Balance Sheets			Net Amount 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	$	339,977		$	(17,640	)	$	322,337		$	—	$	—	$	322,337

	Noncurrent derivative instruments	—			—			—			—		—		—

	Total derivative assets	339,977			(17,640		)	322,337			—		—		322,337

	Liabilities
	Derivative instruments	18,628			(17,640		)	988			—		—		988

	Noncurrent derivative instruments	—			—			—			—		—		—

	Total derivative liabilities	18,628			(17,640		)	988			—		—		988

	Total derivatives	$	321,349		$	—		$	321,349		$	—	$	—	$	321,349




	(in thousands)	31-Dec-13
											Gross Amounts Not Offset in the Balance Sheets
		Gross Amounts Recognized at Fair Value			Gross Amounts Offset in the Balance Sheets			Net Amount 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	$	36,223		$	(18,760	)	$	17,463		$	—	$	—	$	17,463

	Noncurrent derivative instruments	7,992			(2,553		)	5,439			—		—		5,439

	Total derivative assets	44,215			(21,313		)	22,902			—		—		22,902

	Liabilities
	Derivative instruments	49,062			(18,760		)	30,302			—		—		30,302

	Noncurrent derivative instruments	2,553			(2,553		)	—			—		—		—

	Total derivative liabilities	51,615			(21,313		)	30,302			—		—		30,302

	Total derivatives	$	(7,400	)	$	—		$	(7,400	)	$	—	$	—	$	(7,400	)

	Energen had a net $8.2 million deferred tax liability included in current deferred income taxes on the balance sheets related to derivative items included in accumulated other comprehensive income as of December 31, 2013.

	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 thirteen of our active counterparties and in a net loss position with the remaining one at December 31, 2014. The largest counterparty net gain positions at December 31, 2014, J.P. Morgan Ventures Energy Corporation, Merrill Lynch Commodities, Inc., Barclays Bank PLC, Morgan Stanley Capital Group Inc., Canadian Imperial Bank of Commerce and Bank of Montreal, constituted approximately $58.5 million, $46.3 million, $39.0 million, $35.2 million, $34.9 million and $34.3 million, respectively, of Energen’s total net gain on fair value of derivatives.

	The following table details the effect of derivative commodity instruments in cash flow hedging relationships on the financial statements:



	Years ended December 31, (in thousands)	Location on Statements of Income	2014			2013			2012
	Net gain (loss) recognized in other comprehensive income on derivatives (effective portion), net of tax of $23, ($6,660) and $40,720	—	$	37		$	(10,866	)	$	66,438

	Gain reclassified from accumulated other comprehensive income into income (effective portion)	Gain (loss) on derivative instruments, net	$	21,612		$	34,293		$	52,694

Gain (loss) recognized in income on derivatives (ineffective portion and amount excluded from effectiveness testing)	Gain (loss) on derivative instruments, net	$	—		$	835		$	(5,340	)


The following table details the effect of open and closed derivative commodity instruments not designated as hedging instruments on the income statement:



Years ended December 31, (in thousands)	Location on Statements of Income	2014			2013			2012
Gain (loss) recognized in income on derivative	Gain (loss) on derivative instruments, net	$	313,408		$	(73,980	)	$	61,841


During 2013, we had a discontinuance of hedge accounting when Energen determined it was probable certain forecasted volumes would not occur due to certain properties being sold. This discontinuance of hedge accounting resulted in $1.5 million of after-tax losses being recognized into gain (loss) on derivative instruments, net during the year ended December 31, 2014.

As of December 31, 2014, Energen entered into the following transactions for 2015 and subsequent years:



Production Period	Total Hedged Volumes		Average Contract	Description
			Price
Oil
2015	8,280	MBbl	$89.30 Bbl	NYMEX Swaps
Oil Basis Differential
2015	2,160	MBbl	$(4.30) Bbl	WTS/WTI Basis Swaps*
2015	6,840	MBbl	$(4.82) Bbl	WTI/WTI Basis Swaps**
Natural Gas
2015	23	Bcf	$4.13 Mcf	Basin Specific Swaps - San Juan
2015	8	Bcf	$4.25 Mcf	Basin Specific Swaps - Permian
*WTS - West Texas Sour/Midland, WTI - West Texas Intermediate/Cushing
**WTI - West Texas Intermediate/Midland, WTI - West Texas Intermediate/Cushing

As of December 31, 2014, the maximum term over which Energen has hedged exposures to the variability of cash flows is through December 31, 2015.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS




	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:



		December 31, 2014
	(in thousands)	Level 2			Level 3			Total
	Assets
	Derivative instruments	$	294,865		$	27,472		$	322,337

	Total assets	294,865			27,472			322,337

	Liabilities
	Derivative instruments	2,048			(3,036		)	(988		)

	Total liabilities	2,048			(3,036		)	(988		)

	Net derivative asset	$	296,913		$	24,436		$	321,349




		December 31, 2013
	(in thousands)	Level 2			Level 3			Total
	Assets
	Derivative instruments	$	(1,658	)	$	19,121		$	17,463

	Noncurrent derivative instruments	4,383			1,056			5,439

	Total assets	2,725			20,177			22,902

	Liabilities
	Derivative instruments	(28,414		)	(1,888		)	(30,302		)
	Total liabilities	(28,414		)	(1,888		)	(30,302		)
	Net derivative asset (liability)	$	(25,689	)	$	18,289		$	(7,400	)


	At December 31, 2014, Energen had interest rate swap agreements with a notional of $133 million. The interest rate swaps exchange a variable interest rate for a fixed interest rate of 1.0425 percent. The fair value of our interest rate swap was a $0.8 million and a $1.8 million liability at December 31, 2014 and 2013, respectively, and are classified as Level 2 fair value liabilities. The fair value of our interest rate swaps are recognized on a gross basis in accounts payable on the consolidated balance sheet.

	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 $6.7 million change in the fair value of open Level 3 derivative contracts and to the 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:



	Years ended December 31, (in thousands)	2014			2013			2012
	Balance at beginning of period	$	18,289		$	89,019		$	65,801

Realized gains	22,208			55,210			63,720

Unrealized gains (losses) relating to instruments held at the reporting date*	2,981			(71,367		)	22,160

Settlements during period	(19,042		)	(54,573		)	(62,662		)
Balance at end of period**	$	24,436		$	18,289		$	89,019

*Includes $20.2 million in mark-to-market gains, $7.6 million in mark-to-market losses and $19.9 million in mark-to-market gains for the years ended December 31, 2014, 2013 and 2012, respectively.
**Included in the Level 3 fair value at December 31, 2014 are gains of $3.2 million from natural gas liquids and Gas Daily contracts which were closed at December 31, 2014 but not cash settled.

The tables below set 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 December 31, 2014			Valuation Technique*	Unobservable Input*	Range
Oil Basis - WTS/WTI
2015	$	(3,836	)	Discounted Cash Flow	Forward Basis	($2.55 - $2.66) Bbl
Oil Basis - WTI/WTI
2015	$	(14,419	)	Discounted Cash Flow	Forward Basis	($2.72 - $2.82) Bbl
Natural Gas Basis - San Juan
2015	$	28,597		Discounted Cash Flow	Forward Basis	($0.13- $0.14) Mcf

Natural Gas Basis - Permian
2015	$	10,927		Discounted Cash Flow	Forward Basis	($0.15) Mcf

*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 12, Asset Retirement Obligations, for further discussion related to these ARO’s. These assumptions are classified as Level 3 fair value.

Asset Impairments: Energen monitors 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 issues. Such potential events may include, but are not limited to, substantial 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. 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. See Note 13, Asset Impairment, for impairments recognized by Energen during the years ended December 31, 2014, 2013 and 2012
Financial Instruments Not Carried at Fair Value
The stated value of cash and cash equivalents, short-term investments, accounts receivables (net of allowance), and short-term debt approximates fair value due to the short maturity of the instruments. The fair value of Energen’s long-term debt, including the current portion and notes payable to banks, approximates $993.7 million and $1,650.9 million and has a carrying value of $1,039.0 million and $1,643.0 million at December 31, 2014 and 2013, respectively. The fair values were based on market prices of similar issues having the same remaining maturities, redemption terms and credit rating. Short-term debt is classified as Level 1 fair value and long-term debt is classified as Level 2 fair value.

Concentration of Credit Risk
Revenues and related accounts receivable from oil and natural gas operations primarily are generated from the sale of produced oil and natural gas to energy marketing companies. Such sales are typically made on an unsecured credit basis with payment due the month following delivery. This concentration of sales to the energy marketing industry has the potential to affect Energen’s overall exposure to credit risk, either positively or negatively, in that our oil and natural gas purchasers may be affected similarly by changes in economic, industry or other conditions. Energen considers the credit quality of its purchasers and, in certain instances, may require credit assurances such as a deposit, letter of credit or parent guarantee. The two largest purchasers of Energen’s oil and natural gas, Plains Marketing, LP (Plains) and HollyFrontier Corporation (HollyFrontier), accounted for approximately 39 percent and 15 percent, respectively, of Energen’s accounts receivable for commodity sales as of December 31, 2014. Energen’s other purchasers each accounted for less than 9 percent of these accounts receivable as of December 31, 2014. During the year ended December 31, 2014, Plains and HollyFrontier accounted for approximately 37 percent and 13 percent, respectively, of total revenues. All other oil and natural gas purchasers each accounted for less than 10 percent of total revenues for the year ended December 31, 2014.

Exploratory_Costs

Exploratory Costs	12 Months Ended
	Dec. 31, 2014
Extractive Industries [Abstract]
Exploratory Costs	EXPLORATORY COSTS




	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:



	Years ended December 31, (in thousands)	2014			2013			2012
	Capitalized exploratory well costs at beginning of period	$	57,600		$	79,791		$	70,437

	Additions pending determination of proved reserves	946,751			421,599			406,226

	Reclassifications due to determination of proved reserves	(882,254		)	(442,909		)	(396,872		)
	Exploratory well costs charged to expense	(2,658		)	(881		)	—

	Capitalized exploratory well costs at end of period	$	119,439		$	57,600		$	79,791


	The following table sets forth capitalized exploratory wells costs and includes amounts capitalized for a period greater than one year:



	(in thousands)	31-Dec-14			31-Dec-13
	Exploratory wells in progress	$	18,781		$	14,794

	Capitalized exploratory well costs for a period of one year or less	100,658			42,481

	Capitalized exploratory well costs for a period greater than one year	—			1,206

	Total capitalized exploratory well costs	$	119,439		$	58,481


	At December 31, 2014, Energen had 38 gross exploratory wells either drilling or waiting on results from completion and testing. These wells are primarily located in the Permian Basin.

Reconciliation_of_Earnings_Per

Reconciliation of Earnings Per Share	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Reconciliation of Earnings Per Share	RECONCILIATION OF EARNINGS PER SHARE






	Years ended December 31,
	(in thousands, except per share amounts)				2014						2013					2012
		Net			Shares		Per Share Amount		Net		Shares	Per Share Amount		Net		Shares	Per Share Amount
		Income							Income					Income
	Basic EPS	$	568,032		72,897		$	7.79	$	204,554	72,318	$	2.83	$	253,562	72,119	$	3.52

	Effect of dilutive securities
	Stock options				216						112					196

	Non-vested restricted stock				58						20					1

	Performance share awards				104						21					—

	Diluted EPS	$	568,032		73,275		$	7.75	$	204,554	72,471	$	2.82	$	253,562	72,316	$	3.51


	Energen had the following shares that were excluded from the computation of diluted EPS, as inclusion would be anti-dilutive.



	Years ended December 31, (in thousands)	2014		2013		2012
	Stock options	114		134		850

	Non-vested restricted stock	3		7		—

	Performance share awards	2		4		—

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
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 5.4 MMBOE through August 2017.

	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.

	Under oversight of the Site Remediation Section of the Railroad Commission of Texas, Energen Resources is currently in the process of cleanup and remediation of oil and gas wastes in nine reserve pits in Mitchell County, Texas. We estimate that the cleanup, remediation and related costs will approximate $2.5 million of which $1.9 million has been incurred.

	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.

	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.

	Energen Resources previously disclosed an adverse judgment relating to the ownership of the Company operated Cadenhead 25-1 Well (the Cadenhead Well) in Ward County, Texas. Upon a Motion to Reconsider, the adverse judgment was vacated by the District Court in Ward County, Texas and a Summary Judgment Order has been entered confirming Energen Resources’ superior title to the Cadenhead Well and its associated oil and gas leases.

	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 that is now under appeal. In the Revised Order, ONRR has ordered that Energen pay additional royalties on production from certain federal leases in the amount of $129,700. Energen estimates that application of the Revised Order 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 continues to vigorously contest the Revised Order 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 December 31, 2014.

	Lease Obligations: Energen’s total lease payments included as operating lease expense were $24.1 million, $25.0 million and $20.9 million for the years ended December 31, 2014, 2013 and 2012, respectively. Minimum future rental payments required after 2014 under leases with initial or remaining noncancelable lease terms in excess of one year are as follows:



	Years Ending December 31, (in thousands)
	2015	2016	2017	2018	2019	2020 and thereafter
	$2,698	$2,676	$2,468	$2,429	$2,326	$—

Asset_Retirement_Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS




	Energen’s asset retirement obligations 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, 2011	$	107,340

	Liabilities incurred	3,994

	Liabilities settled	(845		)
	Accretion expense (including discontinued operations of $1,195)	7,534

	Balance as of December 31, 2012	118,023

	Liabilities incurred	2,772

	Liabilities settled	(5,525		)
	Accretion expense (including discontinued operations of $1,197)	8,192

	Reclassification associated with held for sale properties*	(14,929		)
	Balance as of December 31, 2013	108,533

	Liabilities incurred	2,266

	Liabilities settled	(1,543		)
	Accretion expense (including discontinued operations of $251)	7,859

	Revision in estimated cash flows	692

	Reclassification associated with held for sale properties**	(23,747		)
	Balance as of December 31, 2014	$	94,060

	*Asset retirement obligation associated with North Louisiana/East Texas properties are included as liabilities related to assets held for sale in current liabilities on the balance sheet.
	**Asset retirement obligation associated with certain San Juan Basin properties are included as liabilities related to assets held for sale in current liabilities on the balance sheet.

Asset_Impairment

Asset Impairment	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Asset Impairment Charges	ASSET IMPAIRMENT




	Impairments recognized by Energen during the years ended December 31, 2014, 2013 and 2012 are presented below:



	Years ended December 31, (in thousands)	2014		2013		2012
	Continuing operations
	Permian Basin oil properties	$	125,693	$	—	$	—

	Permian Basin unproved leasehold properties	55,063		13,906		6,304

	San Juan Basin natural gas properties	236,045		—		—

	Total asset impairments from continuing operations	416,801		13,906		6,304

	Discontinued operations
	North Louisiana/East Texas oil and natural gas properties	1,936		29,794		—

	East Texas oil and natural gas properties	—		—		21,545

	Total asset impairments from discontinued operations	1,936		29,794		21,545

	Total asset impairments	$	418,737	$	43,700	$	27,849


	During the third and fourth quarters of 2014, Energen recognized non-cash impairment writedowns on certain properties in the Permian Basin of $31.2 million pre-tax and $94.5 million pre-tax, respectively, to adjust the carrying amount of these properties to their fair value based on expected future discounted cash flows. These non-cash impairment writedowns are reflected in asset impairment on the consolidated income statement.

	Energen recognized unproved leasehold writedowns primarily on Permian Basin oil properties of $55.1 million pre-tax during the fourth quarter of 2014. These non-cash writedowns are reflected in asset impairment on the consolidated income statement.

	During the third and fourth quarters of 2014, non-cash impairment writedowns of $147.9 million pre-tax and $88.1 million pre-tax, respectively, were recognized by Energen on certain natural gas properties in the San Juan Basin to adjust the carrying amount of these properties to their fair value based on expected future discounted cash flows in the third quarter and based on direct market data in the fourth quarter as these properties were designated as held for sale as of December 31, 2014. These non-cash impairment writedowns are reflected in asset impairment on the consolidated income statement. At December 31, 2014, proved reserves associated with Energen’s San Juan Basin properties totaled 69,043 MBOE.

	In March 2014, Energen completed the sale of its North Louisiana/East Texas natural gas and oil properties for $30.3 million. The sale had an effective date of December 1, 2013, and the proceeds from the sale were used to repay short-term obligations. During the third quarter of 2013, Energen classified these primarily natural gas properties as held for sale and reflected the associated operating results in discontinued operations. Energen recognized non-cash impairment writedowns on these properties in 2014 of $1.9 million pre-tax to adjust the carrying amount of these properties to their fair value based on an estimate of the selling price of the properties. These non-cash impairment writedowns are reflected in gain on disposal of discontinued operations, net in the year ended December 31, 2014. Energen also recognized non-cash impairment writedowns on these properties in the third and fourth quarters of 2013 of $24.6 million pre-tax and $5.2 million pre-tax, respectively. These non-cash impairment writedowns are reflected in gain on disposal of discontinued operations, net in the year ended December 31, 2013. Significant assumptions in valuing the proved reserves included the reserve quantities, anticipated operating costs, anticipated production taxes, future expected natural gas prices and basis differentials, anticipated production declines, and a discount rate of 10 percent commensurate with the risk of the underlying cash flow estimates. The impairment writedowns are classified as Level 3 fair value. At December 31, 2013, proved reserves associated with Energen’s North Louisiana/East Texas properties totaled 23 Bcf of natural gas and 91 MBbl of oil.

	In October 2013, Energen completed the sale of its Black Warrior Basin coalbed methane properties in Alabama for $160 million (subject to closing adjustments). Energen recorded a pre-tax gain on the sale of approximately $35 million in the fourth quarter of 2013 which was reflected in gain on disposal of discontinued operations in the year ended December 31, 2013. The sale had an effective date of July 1, 2013, and the proceeds from the sale were used to repay short-term obligations. The property was classified as held for sale and reflected in discontinued operations during the third quarter of 2013. At December 31, 2012, proved reserves associated with Energen’s Black Warrior Basin properties totaled 97 Bcf of natural gas.

	During the first quarter of 2012, Energen recognized a non-cash impairment writedown on certain properties in East Texas of $21.5 million pre-tax to adjust the carrying amount of these properties to their fair value based on expected future discounted cash flows. This non-cash impairment writedown is reflected in income from discontinued operations for the year ended December 31, 2012. The impairment was caused by the impact of lower future natural gas prices. This impairment writedown is classified as Level 3 fair value.

Acquisition_and_Disposition_of

Acquisition and Disposition of Properties	12 Months Ended
	Dec. 31, 2014
Acquisition and Dispositions of Oil and Gas Properties [Abstract]
Acquisition and Disposition of Properties	ACQUISITION AND DISPOSITION OF PROPERTIES




	In February 2015, Energen entered into a purchase and sale agreement to sell the majority of its natural gas assets in the San Juan Basin in New Mexico and Colorado for approximately $395 million. This sale is expected to close March 31, 2015, and have an effective date of January 1, 2015. At December 31, 2014, proved reserves associated with these San Juan Basin properties totaled 69,043 MBOE.

	During 2014, Energen completed a total of approximately $68.5 million in various purchases of unproved leasehold properties, including the October 2014, purchase of approximately 15,000 net acres of unproved leasehold in the Mancos formation oil play in the San Juan Basin for $22.8 million. During 2013, Energen also completed a total of approximately $26.8 million in various purchases of unproved leasehold properties.

	On February 21, 2012, Energen Resources entered into a definitive agreement with BHP Billiton (BHP) to buy a 50 percent undivided interest in three existing wells in Reeves County, Texas, from Energen Resources for approximately $18 million. Following the purchase of the wells, BHP completed two of the wells and earned a 50 percent undivided interest in 4,829 net acres. The agreement also included the option for BHP to purchase from Energen Resources a 50 percent undivided interest in 51,720 net acres in the Permian Basin. On May 1, 2012, BHP elected not to exercise the option.

	On February 14, 2012, Energen completed the purchase of certain properties in the Permian Basin for a cash purchase price of $68 million. This purchase had an effective date of December 1, 2011. Energen acquired total proved reserves of approximately 8.2 MMBOE. Of the proved reserves acquired, an estimated 81 percent are undeveloped. Approximately 64 percent of the proved reserves are oil, 22 percent are natural gas liquids and natural gas comprises the remaining 14 percent. Energen Resources used its credit facilities and internally generated cash flows to finance the acquisition. Pro forma financial information for this acquisition is not presented because it would not be materially different from the information presented in the consolidated statements of income.

	The following table summarizes the consideration paid and the amounts of the assets acquired and liabilities assumed recognized as of February 14, 2012 (including the effects of closing adjustments).



	(in thousands)
	Consideration given
	Cash (net)	$	67,615

	Recognized amounts of identifiable assets acquired and liabilities assumed
	Proved properties	$	65,581

	Unproved leasehold properties	911

	Accounts receivable	1,358

	Accounts payable	(25		)
	Asset retirement obligation	(210		)
	Total identifiable net assets	$	67,615

	Included in the Company’s consolidated results of operations for the year ended December 31, 2012, were $11.7 million of operating revenues and $3.1 million in operating income resulting from the operation of the properties acquired above.

	In December 2012, Energen completed the purchase of liquids-rich properties in the Permian Basin for a cash purchase price of approximately $18.7 million. During 2012, Energen also completed a total of approximately $18 million in various purchases of unproved leasehold properties.

Discontinued_Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2014
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations	DISCONTINUED OPERATIONS AND HELD FOR SALE PROPERTIES




	On September 2, 2014, Energen completed the transaction to sell Alagasco to Laclede for $1.6 billion, less the assumption of $267 million in debt. The net pre-tax proceeds to Energen totaled approximately $1.32 billion resulting in a pre-tax gain of $726.5 million. This sale has an effective date of August 31, 2014. Energen used cash proceeds from the sale to reduce long-term and short-term indebtedness. During the second quarter of 2014, Energen classified Alagasco as held for sale and reflected the associated operating results in discontinued operations. Energen’s results of operations and cash flows for the years ended December 31, 2014, 2013 and 2012 and our financial position as of December 31, 2014 and 2013 presented in our consolidated financial statements and these notes reflect Alagasco as discontinued operations.

	In March 2014, Energen completed the sale of its North Louisiana/East Texas natural gas and oil properties for $30.3 million. The sale had an effective date of December 1, 2013, and the proceeds from the sale were used to repay short-term obligations. During the third quarter of 2013, Energen classified these primarily natural gas properties as held for sale and reflected the associated operating results in discontinued operations. Energen recognized non-cash impairment writedowns on these properties in 2014 of $1.9 million pre-tax to adjust the carrying amount of these properties to their fair value based on an estimate of the selling price of the properties. These non-cash impairment writedowns are reflected in gain on disposal of discontinued operations, net in the year ended December 31, 2014. Energen also recognized non-cash impairment writedowns on these properties in the third and fourth quarters of 2013 of $24.6 million pre-tax and $5.2 million pre-tax, respectively. These non-cash impairment writedowns are reflected in gain on disposal of discontinued operations, net in the year ended December 31, 2013. At December 31, 2013, proved reserves associated with Energen’s North Louisiana/East Texas properties totaled 23 Bcf of natural gas and 91 MBbl of oil.

	In October 2013, Energen completed the sale of its Black Warrior Basin coalbed methane properties in Alabama for $160 million (subject to closing adjustments). Energen recorded a pre-tax gain on the sale of approximately $35 million in the fourth quarter of 2013 that was reflected in gain on disposal of discontinued operations in the year ended December 31, 2013. The sale had an effective date of July 1, 2013, and the proceeds from the sale were used to repay short-term obligations. The property was classified as held for sale and reflected in discontinued operations during the third quarter of 2013. At December 31, 2012, proved reserves associated with Energen’s Black Warrior Basin properties totaled 97 Bcf of natural gas.

	As discussed in Note 14, Acquisition and Disposition of Properties, and above, the following tables detail held for sale properties by major classes of assets and liabilities:



	(in thousands)	31-Dec-14
					San Juan Basin*
	Oil and natural gas properties				$	1,166,124

	Less accumulated depreciation, depletion and amortization				(770,327		)
	Total assets held for sale				395,797

	Other long-term liabilities				(24,230		)
	Total liabilities held for sale				(24,230		)

	Total net assets held for sale				$	371,567

	*The San Juan Basin natural gas assets which are held for sale as of December 31, 2014, do not qualify for discontinued operations as we will have ongoing operations in the San Juan Basin.


	(in thousands)	31-Dec-13
		Alabama Gas Corporation			Black Warrior Basin			North Louisiana/East Texas			Total
	Cash	$	3,032		$	—		$	—		$	3,032

	Accounts receivable*	103,748			2,829			1,272			107,849

	Inventories	41,200			—			68			41,268

	Oil and natural gas properties	—			—			348,379			348,379

	Less accumulated depreciation, depletion and amortization	—						(301,609		)	(301,609		)

	Utility plant	1,491,433			—			—			1,491,433

	Less accumulated depreciation	(605,924		)	—			—			(605,924		)

	Other property, net	41			—			165			206

	Other current assets*	29,458			—			—			29,458

	Other long-term assets	128,780			—			—			128,780

	Total assets held for sale	1,191,768			2,829			48,275			1,242,872

	Accounts payable	(48,653		)	(1,732		)	(11		)	(50,396		)
	Royalty payable	—			(550		)	(869		)	(1,419		)

	Accrued taxes	(28,027		)	—			—			(28,027		)

	Notes payable to banks	(50,000		)	—			—			(50,000		)

	Other current liabilities*	(105,013		)	(379		)	(21		)	(105,413		)
	Other long-term liabilities	(331,409		)	—			(14,983		)	(346,392		)

Long-term debt	(249,923		)	—			—			(249,923		)

Total liabilities held for sale	(813,025		)	(2,661		)	(15,884		)	(831,570		)
Total net assets held for sale	$	378,743		$	168		$	32,391		$	411,302

*At December 31, 2013, Alagasco’s accounts receivable included a consolidating adjustment of $4.7 million to adjust for affiliated companies receivables. Certain other current assets and other current liabilities at Alagasco of $1.6 million and $0.5 million, respectively, were reclassified to continuing operations at Energen.

We recognized interest on debt required to be extinguished in connection with the sale of Alagasco as discontinued operations. On September 2, 2014, Energen entered into a $1.5 billion five-year syndicated secured credit facility with domestic and foreign lenders. The credit facility was amended to $2.0 billion on November 17, 2014. This credit facility refinances and replaces the $1.25 billion five-year syndicated unsecured credit facility entered into on October 30, 2012. The interest associated with the October 2012 five-year syndicated unsecured credit facilities was classified as discontinued operations. See Note 2, Summary of Significant Accounting Policies, for further information regarding adjustments associated with the sale of Alagasco.

During the first quarter of 2012, Energen recognized a non-cash impairment writedown on certain properties in East Texas of $21.5 million pre-tax to adjust the carrying amount of these properties to their fair value based on expected future discounted cash flows. This non-cash impairment writedown is reflected in income from discontinued operations for the year ended December 31, 2012. The impairment was caused by the impact of lower future natural gas prices. This impairment writedown is classified as Level 3 fair value.



Years ended December 31, (in thousands, except per share data)	2014			2013			2012
Natural gas distribution revenues	$	397,648		$	533,338		$	451,589

Oil and natural gas revenues	5,199			60,191			76,350

Total revenues	$	402,847		$	593,529		$	527,939

Pretax income from discontinued operations	$	47,220		$	92,253		$	79,197

Income tax expense	17,928			33,174			30,256

Income From Discontinued Operations	$	29,292		$	59,079		$	48,941

Gain on disposal of discontinued operations, net	$	724,594		$	5,605		$	—

Income tax expense	285,497			2,011			—

Gain on Disposal of Discontinued Operations, net	$	439,097		$	3,594		$	—

Total Income From Discontinued Operations	$	468,389		$	62,673		$	48,941

Diluted Earnings Per Average Common Share
Income from discontinued operations	$	0.4		$	0.81		$	0.68

Gain on disposal of discontinued operations, net	5.99			0.05			—

Total Income From Discontinued Operations	$	6.39		$	0.86		$	0.68

Basic Earnings Per Average Common Share
Income from discontinued operations	$	0.4		$	0.82		$	0.68

Gain on disposal of discontinued operations, net	6.02			0.05			—

Total Income From Discontinued Operations	$	6.42		$	0.87		$	0.68

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2014
Supplemental Cash Flow Information [Abstract]
Supplemental Cash Flow Information	SUPPLEMENTAL CASH FLOW INFORMATION




	Supplemental information concerning Energen’s cash flow activities from continuing operations was as follows:



	Years ended December 31, (in thousands)	2014		2013		2012
	Interest paid, net of amount capitalized	$	32,172	$	38,255	$	46,224

	Income taxes paid	$	219,505	$	22,781	$	18,023

	Noncash investing activities:
	Accrued development, exploration costs and other capital	$	207,461	$	93,623	$	116,488

	Capitalized asset retirement obligations costs	$	2,958	$	2,772	$	3,994

	Capital lease obligations	$	—	$	—	$	5,072

	Receivable from sale of Alabama Gas Corporation	$	8,247	$	—	$	—

	Noncash financing activities:
	Issuance of common stock for employee benefit plans	$	2,448	$	1,015	$	838

	Treasury stock acquired in connection with tax withholdings	$	2,547	$	977	$	277

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2014
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)	Cash Flow Hedges			Pension and Postretirement Plans			Total
	Balance as of December 31, 2013	$	12,178		$	(32,245	)	$	(20,067	)

	Other comprehensive loss before reclassifications	(261		)	(5,056		)	(5,317		)
	Amounts reclassified from accumulated other comprehensive income (loss)	(11,917		)	14,431			2,514

	Change in accumulated other comprehensive income (loss)	(12,178		)	9,375			(2,803		)

	Balance as of December 31, 2014	$	—		$	(22,870	)	$	(22,870	)


	The following table provides details of the reclassifications out of accumulated other comprehensive income (loss).



	Years ended December 31, (in thousands)	2014			2013
	(in thousands)	Amounts Reclassified						Line Item Where Presented
	Gains (losses) on cash flow hedges:
	Commodity contracts	$	21,611		$	35,684		Gain (loss) on derivative instruments, net

	Interest rate swap	(2,280		)	(1,723		)	Interest expense
	Total cash flow hedges	19,331			33,961

	Income tax expense	(7,414		)	(12,957		)
	Net of tax	11,917			21,004

	Pension and postretirement plans:
	Transition obligation	(22		)	(319		)	General and administrative
	Prior service cost	(248		)	(257		)	General and administrative
	Actuarial losses*	(21,932		)	(12,357		)	General and administrative
	Actuarial losses on settlement charges*	—			(421		)	Assets held for sale

	Total pension and postretirement plans	(22,202		)	(13,354		)
	Income tax benefit	7,771			4,674

	Net of tax	(14,431		)	(8,680		)
	Total reclassifications for the period	$	(2,514	)	$	12,324

	*In the first quarter of 2013, Energen incurred a settlement charge of $0.5 million for the payment of lump sums from the nonqualified supplemental retirement plans, of which $0.1 million was recognized in actuarial losses above and $0.4 million was recognized as a regulatory asset at Alagasco and reported in actuarial losses on settlement charges above. In the third quarter of 2013, Energen incurred a settlement charge of $64,000 for the payment of lump sums from the nonqualified supplemental retirement plans, of which $18,000 was recognized in actuarial losses above and $46,000 was recognized as a regulatory asset at Alagasco and reported in actuarial losses on settlement charges above.

Recently_Issued_Accounting_Sta

Recently Issued Accounting Standards	12 Months Ended
Recently Issued Accounting Standards	Dec. 31, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recently Issued Accounting Standards	RECENTLY ISSUED ACCOUNTING STANDARDS




	In April 2014, the Financial Accounting Standards Board issued Accounting Standards Update (ASU) No. 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity. This update defines a discontinued operation as a disposal of a component or a group of components that is disposed of or is classified as held for sale and represents a strategic shift that has (or will have) a major effect on an entity’s operations and financial results. The amendment is effective for all annual periods beginning on or after December 15, 2014, and interim periods within those annual periods. Energen does not expect the adoption of this ASU to have a material impact on its consolidated financial statements.

Summarized_Quarterly_Financial

Summarized Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Data [Abstract]
Summarized Quarterly Financial Information (Unaudited)	SUMMARIZED QUARTERLY FINANCIAL DATA *(Unaudited)*




	The following data summarizes quarterly operating results.



		Year ended December 31, 2014
	(in thousands, except per share amounts)	First			Second			Third			Fourth
	Revenues as originally reported	$	561,178		$	270,097		$	497,761		$	611,435

	Discontinued operations*	(263,900		)	—			—			—

	Adjusted revenues	$	297,278		$	270,097		$	497,761		$	611,435

	Operating income as originally reported	$	104,599		$	3,107		$	48,171		$	94,223

	Discontinued operations*	(73,139		)	—			—			—

	Adjusted operating income	$	31,460		$	3,107		$	48,171		$	94,223

	Income (loss) from continuing operations	$	15,647		$	(3,154	)	$	20,631		$	66,519

	Net income (loss)	$	53,316		$	(7,953	)	$	457,251		$	65,418

	Diluted earnings per average common share
	Continuing operations	$	0.21		$	(0.04	)	$	0.28		$	0.91

	Net income (loss)	$	0.73		$	(0.11	)	$	6.22		$	0.89

	Basic earnings per average common share
	Continuing operations	$	0.22		$	(0.04	)	$	0.28		$	0.91

	Net income (loss)	$	0.73		$	(0.11	)	$	6.26		$	0.9




		Year ended December 31, 2013
	(in thousands, except per share amounts)	First			Second			Third			Fourth
	Revenues as originally reported	$	492,679		$	490,057		$	320,406		$	472,733

	Discontinued operations*	(256,348		)	(123,076		)	(48,368		)	(142,771		)
	Adjusted revenues	$	236,331		$	366,981		$	272,038		$	329,962

	Operating income as originally reported	$	105,336		$	146,304		$	(4,052	)	$	110,630

	Discontinued operations*	(84,146		)	(7,667		)	21,487			(35,755		)

	Adjusted operating income	$	21,190		$	138,637		$	17,435		$	74,875

	Income from continuing operations	$	8,419		$	82,422		$	5,407		$	45,633

	Net income (loss)	$	56,692		$	83,067		$	(19,298	)	$	84,093

	Diluted earnings per average common share
	Continuing operations	$	0.12		$	1.14		$	0.07		$	0.62

	Net income (loss)	$	0.78		$	1.15		$	(0.27	)	$	1.15

	Basic earnings per average common share
	Continuing operations	$	0.12		$	1.14		$	0.07		$	0.63

Net income (loss)	$	0.79		$	1.15		$	(0.27	)	$	1.16

*As discussed in Note 15, Discontinued Operations and Held for Sale Properties, during the third quarter of 2014, Energen completed the transaction to sell Alagasco to Laclede. During the second quarter of 2014, Energen classified Alagasco as held for sale and reflected the associated operating results in discontinued operations. During the fourth quarter of 2013, Energen completed the sale of its Black Warrior Basin coalbed methane properties in Alabama. The property was classified as held for sale and reflected in discontinued operations during the third quarter of 2013. Also, during the third quarter of 2013, Energen classified its North Louisiana/East Texas natural gas and oil properties as held for sale and reflected the associated operating results in discontinued operations.

Oil_and_Natural_Gas_Operations

Oil and Natural Gas Operations (Unaudited) Oil and Natural Gas Operations (Unaudited)	12 Months Ended
	Dec. 31, 2014
Oil and Gas Exploration and Production Industries Disclosures [Abstract]
Oil and Natural Gas Operations (Unaudited)	OIL AND NATURAL GAS OPERATIONS *(Unaudited)*




	Capitalized Costs: The following table sets forth capitalized costs:



	(in thousands)	December 31, 2014			December 31, 2013
	Proved	$	8,069,638		$	7,043,779

	Unproved	142,340			168,975

	Total capitalized costs	8,211,978			7,212,754

	Accumulated depreciation, depletion and amortization	2,663,434			2,078,411

	Capitalized costs, net	$	5,548,544		$	5,134,343


	Costs Incurred: The following table sets forth costs incurred in property acquisition, exploration and development activities and includes both capitalized costs and costs charged to expense during the year:



	Years ended December 31, (in thousands)	2014			2013			2012
	Property acquisition:
	Proved	$	2,582		$	4,661		$	79,862

	Unproved	68,514			26,820			58,634

	Exploration	972,164			435,636			419,284

	Development	408,949			655,353			749,256

	Total costs incurred	$	1,452,209		$	1,122,470		$	1,307,036


	Results of Operations From Producing Activities: The following table sets forth results of Energen’s oil, natural gas liquids and natural gas operations from producing activities:



	Years ended December 31, (in thousands)	2014			2013			2012
	Gross revenues*	$	1,679,213		$	1,206,293		$	1,090,948

	Production (lifting costs)	376,495			351,541			278,193

	Exploration expense	28,090			14,036			13,052

	Depreciation, depletion and amortization including asset impairments	960,539			463,606			345,873

	Accretion expense	7,608			6,995			6,339

	Income tax expense	99,469			128,773			160,551

	Results of operations from producing activities	$	207,012		$	241,342		$	286,940

	* The years ended December 31, 2014, 2013 and 2012 gross revenues include a pre-tax non-cash mark-to-market gain on derivatives of $315.4 million, a pre-tax non-cash mark-to-market loss on derivatives of $47.8 million and a pre-tax non-cash mark-to-market gain on derivatives of $58.8 million, respectively.

	Oil and Natural Gas Operations: The calculation of proved reserves is made pursuant to rules prescribed by the SEC. Such rules, in part, require that proved categories of reserves be disclosed. Proved reserves and associated values were calculated using twelve-month average prices and current costs for the years ended December 31, 2014, 2013 and 2012. Changes to prices and costs could have a significant effect on the disclosed amount of proved reserves and their associated values. In addition, the estimation of proved reserves inherently requires the use of geologic and engineering estimates which are subject to revision as reservoirs are produced and developed and as additional information is available. Accordingly, the amount of actual future production may vary significantly from the amount of proved reserves disclosed. The proved reserves are located onshore in the United States of America.

	Estimates of physical quantities of oil and natural gas proved reserves were determined by Company engineers. Ryder Scott Company, L.P. (Ryder Scott) and T. Scott Hickman and Associates, Inc. (T. Scott Hickman), independent oil and natural gas reservoir engineers, have audited the estimates of proved reserves of oil, natural gas liquids and natural gas that Energen has attributed to its net interests in oil and natural gas properties as of December 31, 2014. Ryder Scott audited the proved reserve estimates for coalbed methane in the San Juan Basin and substantially all of the Permian Basin proved reserves. T. Scott Hickman audited the conventional proved reserves in the San Juan Basin. The independent reservoir engineers have issued reports covering approximately 99 percent of Energen’s ending proved reserves indicating that in their judgment the estimates are reasonable in the aggregate.



Year ended December 31, 2014	Oil MBbl		NGL MBbl		Natural Gas MMcf		Total MMBOE
Proved reserves at beginning of period	164,870		63,011		719,725		347.8

Revisions of previous estimates	(48,548	)	(15,165	)	(71,806	)	(75.7	)
Purchases	88		26		116		0.1

Extensions and discoveries	76,722		29,695		141,209		130

Production	(11,818	)	(4,104	)	(59,562	)	(25.8	)
Sales	(87	)	—		(21,756	)	(3.7	)

Proved reserves at end of period	181,227		73,463		707,926		372.7

Proved developed reserves at end of period	118,697		47,621		589,074		264.5

Proved undeveloped reserves at end of period	62,530		25,842		118,852		108.2




Year ended December 31, 2013	Oil MBbl		NGL MBbl		Natural Gas MMcf		Total MMBOE
Proved reserves at beginning of period	155,348		56,155		809,128		346.4

Revisions of previous estimates	(680	)	2,211		18,465		4.6

Purchases	142		56		282		0.2

Extensions and discoveries	20,517		7,823		50,568		36.8

Production	(10,378	)	(3,233	)	(70,506	)	(25.4	)
Sales	(79	)	(1	)	(88,212	)	(14.8	)
Proved reserves at end of period	164,870		63,011		719,725		347.8

Proved developed reserves at end of period	113,795		42,087		623,305		259.8

Proved undeveloped reserves at end of period	51,075		20,924		96,420		88




Year ended December 31, 2012	Oil MBbl		NGL MBbl		Natural Gas MMcf		Total MMBOE
Proved reserves at beginning of period	129,578		53,957		957,368		343.1

Revisions of previous estimates	(8,546	)	(9,557	)	(143,704	)	(42.1	)
Purchases	7,950		2,569		10,656		12.4

Extensions and discoveries	35,132		11,759		61,170		57.1

Production	(8,766	)	(2,573	)	(76,362	)	(24.1	)
Proved reserves at end of period	155,348		56,155		809,128		346.4

Proved developed reserves at end of period	105,976		36,440		708,657		260.5

Proved undeveloped reserves at end of period	49,372		19,715		100,471		85.9


2014 Activities: Energen had net downward reserve revisions during 2014 which totaled 75.7 MMBOE including downward revisions of approximately 53.4 MMBOE of proved undeveloped reserves that are now expected to be drilled after the original five year period and upward revisions of approximately 3.9 MMBOE related to changes in year-end pricing. The San Juan Basin had upward reserve revisions of 1.6 MMBOE including 4.4 MMBOE related to changes in year-end pricing and downward revisions of approximately 1.5 MMBOE due to higher operating costs. Net downward reserve revisions of 77.3 MMBOE in the Permian Basin were due to reclassifying 53.4 MMBOE as unproved because of changes in our development plans, downward revisions of approximately 13.3 MMBOE due to decreased well performance in certain Wolfberry wells, downward revisions of approximately 5.4 due to higher operating costs and approximately 0.5 MMBOE related to changes in the year-end pricing.

Energen purchased 0.1 MMBOE of reserves during 2014 primarily related to the acquisitions of oil properties in the Permian Basin.

During 2014, Energen had extensions and discoveries of 130.0 MMBOE of which 70 percent were proved undeveloped reserves and 30 percent were proved developed reserves. Extension drilling resulted in 89.6 MMBOE of discoveries with exploratory drilling providing 40.4 MMBOE of discoveries. The San Juan Basin added 1.1 MMBOE of reserves through the drilling or identification of 16 well locations and 10 pay adds. The Permian Basin added 128.6 MMBOE of reserves primarily through the drilling or identification of 361 well locations.

During 2014, Energen had sales of 3.7 MMBOE primarily due to the sale of the North Louisiana/East Texas primarily natural gas properties.

2013 Activities: Energen had upward reserve revisions during 2013 which totaled 4.6 MMBOE including approximately 7 MMBOE related to changes in year-end pricing and downward revisions of approximately 5.3 MMBOE of proved undeveloped reserves of which 4.6 MMBOE are expected to be drilled beyond five years with the remainder no longer expected to be drilled. The San Juan Basin upward reserve revisions of 2.2 MMBOE including 5.9 MMBOE related to changes in year-end pricing and downward revisions of approximately 4.6 MMBOE of proved undeveloped reserves that are expected to be drilled beyond five years. Net upward reserve revisions of 1.2 MMBOE in the Permian Basin were due to improved well performance in certain Wolfberry wells and approximately 0.4 MMBOE related to changes in the year-end pricing and downward revisions of approximately 0.7 MMBOE of proved undeveloped reserves that are no longer expected to be drilled.

Energen purchased 0.2 MMBOE of reserves during 2013 primarily related to the acquisitions of oil properties in the Permian Basin.

During 2013, Energen had extensions and discoveries of 36.8 MMBOE of which 45 percent were proved undeveloped reserves and 55 percent were proved developed reserves. Extension drilling resulted in 21.6 MMBOE of discoveries with exploratory drilling providing 15.2 MMBOE of discoveries. The San Juan Basin added 2.3 MMBOE of reserves through 30 pay adds. The Permian Basin added 34.4 MMBOE of reserves primarily through the drilling or identification of 262 well locations.

During 2013, Energen had sales of 14.8 MMBOE primarily due to the sale of the Black Warrior Basin coalbed methane properties.

2012 Activities: Energen had downward reserve revisions during 2012 which totaled 42.1 MMBOE. The Black Warrior Basin had downward reserve revisions totaling 5.1 MMBOE of which approximately 5.9 MMBOE related to estimated negative price related revisions partially offset by better well performance. The San Juan Basin downward reserve revisions of 19.7 MMBOE included 22.5 MMBOE in negative price related revisions partially offset by better well performance, lower operating costs and lower fuel usage. Downward reserve revisions of 15.8 MMBOE in the Permian Basin were primarily due to lower than anticipated performance in certain development wells along with 1.0 MMBOE of estimated negative price related revisions.

Energen purchased 12.4 MMBOE of reserves during 2012 primarily related to the acquisitions of oil properties in the Permian Basin.

During 2012, Energen had extensions and discoveries of 57.1 MMBOE of which 59 percent were proved undeveloped reserves and 41 percent were proved developed reserves. Extension drilling resulted in 45.6 MMBOE of discoveries with exploratory drilling providing 11.5 MMBOE of discoveries. The San Juan Basin added 0.9 MMBOE of reserves through the drilling or identification of 6 well locations. The Permian Basin added 56.1 MMBOE of reserves primarily through the drilling or identification of 422 well locations.









Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Natural Gas Reserves: The standardized measure of discounted future net cash flows is not intended, nor should it be interpreted, to present the fair market value of Energen’s crude oil and natural gas reserves. An estimate of fair market value would take into consideration factors such as, but not limited to, the recovery of reserves not presently classified as proved reserves, anticipated future changes in prices and costs, and a discount factor more representative of the time value of money and the risks inherent in reserve estimates. At December 31, 2014, 2013 and 2012, Energen had a deferred hedging gain of $315.4 million, a deferred hedging gain of $21.6 million and a deferred hedging gain of $74.8 million, respectively, all of which are excluded from the calculation of standardized measure of future net cash flows.



Years ended December 31, (in thousands)	2014			2013			2012
Future gross revenues	$	20,971,672		$	19,509,305		$	17,735,363

Future production costs	7,532,273			6,136,709			5,715,248

Future development costs	1,784,738			1,896,602			1,892,600

Future income tax expense	3,440,582			3,209,697			2,809,411

Future net cash flows	8,214,079			8,266,297			7,318,104

Discount at 10% per annum	3,994,423			4,248,456			3,618,785

Standardized measure of discounted future net cash	$	4,219,656		$	4,017,841		$	3,699,319
flows relating to proved oil and natural gas reserves

The following are the principal sources of changes in the standardized measure of discounted future net cash flows:



Years ended December 31, (in thousands)	2014			2013			2012
Balance at beginning of year	$	4,017,841		$	3,699,319		$	3,629,163

Revisions to reserves proved in prior years:
Net changes in prices, production costs and future development costs	(1,147,028		)	566,838			(922,792		)

Net changes due to revisions in quantity estimates	(1,285,394		)	(81,762		)	(383,755		)
Development costs incurred, previously estimated	337,198			299,432			472,603

Accretion of discount	401,784			369,932			362,916

Changes in timing and other*	987,652			(179,502		)	(317,244		)

Total revisions	(705,788		)	974,938			(788,272		)

New field discoveries and extensions, net of future production and development costs	2,321,028			376,326			1,025,419

Sales of oil and gas produced, net of production costs	(1,054,553		)	(1,014,593		)	(812,781		)
Purchases	4,241			4,690			189,755

Sales	(21,092		)	(24,876		)	—

Net change in income taxes	(342,021		)	2,037			456,035

Net change in standardized measure of discounted future net cash flows	201,815			318,522			70,156

Balance at end of year	$	4,219,656		$	4,017,841		$	3,699,319

*Amount represents changes in production timing and other. For 2014, the production timing is significantly affected by changes related to the acceleration of the horizontal drilling program and the delay of the vertical drilling program.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation

	The accompanying consolidated financial statements include Energen and its subsidiaries, principally Energen Resources, after elimination of all significant intercompany transactions in consolidation. In the opinion of management, our consolidated financial statements reflect all adjustments necessary to present fairly 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.
Property and Related Depletion	Property and Related Depletion: Energen follows the successful efforts method of accounting for costs incurred in the exploration and development of oil, natural gas liquids and natural gas reserves. Lease acquisition costs are capitalized initially, and unproved properties are reviewed periodically to determine if there has been impairment of the carrying value, with any such impairment charged to exploration expense currently. All development costs are capitalized. 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, we continue 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) we are making sufficient progress assessing the reserves and the economic and operating viability of the project. Capitalized exploratory drilling costs are presented in unproved properties in the balance sheets. If the exploratory well is determined to be a dry well, the costs are charged to exploration expense. Other exploration costs, including geological and geophysical costs, are expensed as incurred. Depreciation, depletion and amortization expense is determined on a field-by-field basis using the units-of-production method based on proved reserves. Anticipated abandonment and restoration costs are capitalized and depreciated using the units-of-production method based on proved developed reserves.
Operating Revenues	Operating Revenues: Energen utilizes the sales method of accounting to recognize oil, natural gas liquids and natural gas production revenue. Under the sales method, revenues are based on actual sales volumes of commodities sold to purchasers. Over-production liabilities are established only when it is estimated that a property’s over-produced volumes exceed the net share of remaining proved reserves for such property.
Derivative Commodity Instruments	Derivative Commodity Instruments: We periodically enter into derivative commodity instruments to hedge our exposure to price fluctuations on oil, natural gas and natural gas liquids production. Such instruments may include over-the-counter (OTC) swaps and basis swaps typically executed with investment and commercial banks and energy-trading firms. All derivative commodity instruments in a gain position are valued on a discounted basis incorporating an estimate of performance risk specific to each related counterparty. Derivative commodity instruments in a loss position are valued on a discounted basis incorporating an estimate of performance risk specific to Energen. All derivative transactions are included in operating activities on the consolidated statements of cash flows.

	Energen’s current policy is to not enter into agreements that require the posting of collateral. The majority of our counterparty agreements include provisions for net settlement of transactions payable on the same date and in the same currency. Most of the agreements include various contractual set-off rights, which may be exercised by the non-defaulting party in the event of an early termination due to a default.

	Prior to June 30, 2013, Energen used cash flow hedge accounting, where applicable, for its derivative transactions. The effective portion of the gain or loss on the derivative instrument was recognized in accumulated other comprehensive income as a component of shareholders’ equity and subsequently reclassified as gain (loss) on derivative instruments, net when the forecasted transaction affects earnings. The ineffective portion of a derivative’s change in fair value was required to be recognized immediately in gain (loss) on derivative instruments, net. All other derivative transactions not designated as cash flow hedge accounting 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.

	Effective March 31, 2013 and June 30, 2013, Energen dedesignated from cash flow hedge accounting 5,078 thousand barrels (MBbl) and 2,353 MBbl, respectively, of various NYMEX oil contracts with the Permian Basin due to lack of correlation. Gains and losses from inception of the hedge to the dedesignation date were frozen in accumulated other comprehensive income until the forecasted transactions actually occurred. Subsequent gains or losses are accounted for as mark-to-market transactions and recognized immediately through gain (loss) on derivative instruments, net.

	Effective June 30, 2013, Energen discontinued the use of cash flow hedge accounting and dedesignated all remaining derivative commodity instruments that were previously designated as cash flow hedges. As a result of discontinuing hedge accounting, any gains or losses from inception of the hedge to June 30, 2013 were frozen in accumulated other comprehensive income until the forecasted transactions actually occurred. Any subsequent gains or losses are accounted for as mark-to-market and recognized immediately through gain (loss) on derivative instruments, net. As a result of Energen’s election to discontinue hedge accounting, all derivative transactions entered into subsequent to June 30, 2013 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.

	Derivative transactions are pursuant to standing authorizations by the Board of Directors, which do not authorize speculative positions. Energen formally documents all relationships between hedging instruments and hedged items at the inception of the hedge, as well as its risk management objective and strategy for undertaking the hedge. This process includes specific identification of the hedging instrument and the nature of the risk being hedged. Our credit facility also limits our ability to enter into commodity hedges based on projected production volumes.
Asset Impairments	Asset Impairments: Oil and natural gas proved properties periodically are assessed for possible impairment on a field-by-field basis using the estimated undiscounted future cash flows. Impairment losses are recognized when the estimated undiscounted future cash flows are less than the current net book values of the properties in a field. Energen monitors its oil and natural gas properties as well as the market and business environments in which it operates and makes assessments about events that could result in potential impairment issues. Such potential events may include, but are not limited to, substantial commodity price declines, unanticipated increased operating costs, and lower than expected production performance. If a material event occurs, we make an estimate of undiscounted future cash flows to determine whether the asset is impaired. If the asset is impaired, Energen 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.

	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 variables can, and often do, differ from the estimates and can have a positive or negative impact on our need for impairment or on the amount of impairment. In addition, further changes in the economic and business environment can impact Energen’s original and ongoing assessments of potential impairment.

	Energen also may recognize impairments of capitalized costs for unproved properties. The greatest portion of these costs generally relate to the acquisition of leasehold. The costs are capitalized and periodically evaluated as to recoverability, based on changes brought about by exploration activities, changes in economic factors and potential shifts in business strategy employed by management. We consider a combination of geologic and economic factors to evaluate the need for impairment of these costs.
Long-Lived Assets and Discontinued Operations	Long-Lived Assets and Discontinued Operations: Energen may, in the ordinary course of business, be involved in the sale of developed or undeveloped properties. All assets held for sale are reported at the lower of the carrying amount or estimated fair value. Certain of these held for sale properties also qualify as discontinued operations when the sale results in the elimination of operations and cash flows from company operations and when there will be no significant continuing involvement in the operations and cash flows of the sold component. The results of operations of these properties are reclassified and reported as discontinued operations for prior periods.
Acquisitions	Acquisitions: Energen recognizes all acquisitions at fair value. Energen estimates the fair value of the assets acquired and liabilities assumed as of the acquisition date, the date on which Energen obtained control of the properties for all acquisitions that qualify as business combinations. The 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). Fair value measurements also utilize assumptions of market participants. Energen uses a discounted cash flow model and makes market assumptions as to future commodity prices, projections of estimated quantities of oil and natural gas reserves, expectations for timing and amount of future development and operating costs, projections of future rates of production, expected recovery rates and risk adjusted discount rates. These assumptions represent Level 3 inputs under the fair value hierarchy. Acquisition related costs are expensed as incurred in G&A expense on the consolidated income statements.
Inventories	Inventory

	Inventories consist primarily of tubular goods and other oilfield equipment used in our operations and are stated at the lower of cost or market value, on a weighted average cost basis.
Fair Value Measurements	Fair Value Measurements

	The carrying values of cash and cash equivalents, accounts payable, accounts receivable (net of allowance), derivative commodity instruments, pension and postretirement plan assets and liabilities and other current assets and liabilities approximate fair value. 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 assumptions 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.

	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 directly observable market prices are classified within Level 2 of the fair value hierarchy. These Level 2 fair values consist of swaps 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 basin specific, 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, we maintain communications with our counterparties and discuss pricing practices. Further, we corroborate the fair value of our transactions by comparison of market-based price sources.

	Energen utilizes a discounted cash flow model in valuing its interest rate derivatives, which are comprised of interest rate swap agreements. The fair value attributable to Energen's interest rate derivative contracts is based on (i) the contracted notional amounts, (ii) active market-quoted LIBOR yield curves and (iii) the applicable credit-adjusted risk-free rate yield curve.

	Pension and postretirement plan assets include cash and mutual funds. Plan assets were classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The determination and classification of fair value requires judgment and may affect the valuation of fair value assets and their placement within the fair value hierarchy. Level 1 and Level 2 fair values use market transactions and other market evidence whenever possible and consist primarily of equities, fixed income and mutual funds. Level 3 fair values used unobservable market prices primarily associated with certain alternative investments and a limited partnership in 2013 and 2012.
Income Taxes	Income Taxes

	Energen uses the liability method of accounting for income taxes. Under this method, a deferred tax asset or liability is recognized for the estimated future tax effects attributable to temporary differences between the financial statement basis and the tax basis of assets and liabilities as well as tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the period of the change. Energen and its subsidiaries file a consolidated federal income tax return. Consolidated federal income taxes are charged to appropriate subsidiaries using the separate return method.
Accounts Receivable and Allowance for Doubtful Accounts	Accounts Receivable and Allowance for Doubtful Accounts

	Trade accounts receivable are recorded at the invoiced amounts and do not bear interest. The allowance for doubtful accounts is our best estimate of the amount of probable credit losses in the existing accounts receivable. Energen determines the allowance based on historical experience and in consideration of current market conditions. Account balances are charged against the allowance when it is anticipated the receivable will not be recovered.
Cash and Cash Equivalents	Cash and Cash Equivalents

	Cash and cash equivalents consist of cash in banks and investments readily convertible into cash, which have original maturities within three months at the date of acquisition. Cash equivalents are stated at cost, which approximates fair value.
Short-term investments	Short-term Investments

	All highly liquid financial instruments with maturities greater than three months and less than one year at the date of purchase are considered to be short-term investments.
Earnings Per Share (EPS)	Earnings Per Share (EPS)

	Energen’s basic earnings per share amounts have been computed based on the weighted average number of common shares outstanding. Diluted earnings per share amounts reflect the assumed issuance of common shares for all potentially dilutive securities.
Stock-Based Compensation	Stock-Based Compensation

	Energen measures all share-based compensation awards at fair value at the date of grant and expenses the awards over the requisite vesting period. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if the actual forfeitures differ from those estimates. We recognize all stock-based compensation expense in the period of grant, subject to certain vesting requirements, for retirement eligible employees. Energen utilizes the long-form method of calculating the available pool of windfall tax benefit.
Estimates	Estimates

	The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and the reported amount of revenues and expenses during the reporting period. The major estimates and assumptions identified by management include, but are not limited to, physical quantities of proved oil and gas reserves, periodic assessments of oil and gas properties for impairment, Energen’s obligations under its employee pension and compensation plans, the valuation of derivative financial instruments, the allowance for doubtful accounts, tax contingency reserves, legal contingency reserves, asset retirement obligations and self insurance reserves. Due to the inherent uncertainty involved in making estimates, actual results reported in future periods may differ from the estimates.
Employee Benefit Plans	Employee Benefit Plans

	Energen has a defined benefit non-contributory qualified pension plan which covers substantially all employees. Pension benefits are based on years of service and final earnings. Energen also has nonqualified supplemental pension plans covering certain officers of Energen. In addition to providing pension benefits, Energen provides certain postretirement health care and life insurance benefits for all employees hired prior to January 1, 2010. These postretirement healthcare and life insurance benefits are available upon reaching normal retirement age while working for Energen. The projected unit credit actuarial method was used to determine the normal cost and actuarial liability.

	Plan Separation: Effective April 30, 2014, Energen separated its defined benefit non-contributory pension plan and its postretirement healthcare and life insurance benefit plan into an Energen and an Alagasco plan reflecting the separation of assets and obligations in accordance with ERISA provisions. Energen remeasured the plans using current assumptions.

	Plan Termination: 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 closes the plan to new entrants, effective November 1, 2014, and freezes benefit accruals effective December 31, 2014. Energen terminated the plan on January 31, 2015. We anticipate distributing benefits under the plan in late 2015 or early 2016 pending receipt of a determination letter from the IRS and completion of certain administrative actions.

	Energen’s non-qualified supplemental retirement plans have also been amended to terminate effective December 31, 2014. Distributions under the plan are subject to certain payment restrictions under the Internal Revenue Code and Treasury regulations and payments to plan participants will be made in each of the first quarters of 2015 and 2016.

	Measurement: For retirement plans and other postretirement plans, certain financial assumptions are used in determining Energen’s projected benefit obligation. These assumptions are examined periodically by Energen, and any required changes are reflected in the subsequent determination of projected benefit obligations.

	Energen calculates periodic expense for the defined benefit pension plan and other postretirement benefit plans on an actuarial basis and the net funded status of benefit plans is recognized as an asset or liability in its statement of financial position with changes in the funded status recognized through comprehensive income. For the pension plan, the benefit obligation is the projected benefit obligation calculated on a plan termination basis assuming a distribution in one year; for other postretirement plans, the benefit obligation is the accumulated postretirement benefit obligation. Energen measures the funded status of its employee benefit plans as of the date of its year-end statement of financial position.

	Discount Rate: For our defined benefit pension plan, we discounted the estimated termination liability using the one year spot rate of 0.70 percent. For our other postretirement plan, we selected a yield curve comprised of a broad base of Aa bonds with maturities between zero and thirty years. The discount rate for the postretirement plan was developed as the level equivalent rate that would produce the same present value as that using spot rates aligned with the projected benefit payments.

	Long-Term Rate of Return: The assumed rate of return on assets is the weighted average of expected long-term asset assumptions. Energen considered past performance and current expectations for assets held by the plans as well as the expected long-term allocation of plan assets.

	Other Significant Assumptions: The estimated weighted average rate of increase in the compensation level for pay related plans is another assumption used in calculation of the net periodic pension cost
Environmental Costs	Environmental Costs

	Environmental compliance costs, including ongoing maintenance, monitoring and similar costs, are expensed as incurred. Environmental remediation costs are accrued when remedial efforts are probable and the cost can be reasonably estimated.
Investment Strategy	Investment Strategy: Due to the plan termination of our defined benefit plans, we have transitioned our investment strategy to reduce risk. We liquidated our equity and debt securities and have invested fully in cash and cash equivalents at year-end. We expect to hold these funds along with any additional contributions in cash until the benefits are fully distributed.

	For our postretirement benefit plan assets, we continue to employ a total return investment approach whereby a mix of equities and fixed income investments are used to maximize the long-term return of plan assets with a prudent level of risk. Risk tolerance is established through consideration of plan liabilities, plan funded status, corporate financial condition and market conditions.

	Energen seeks to maintain an appropriate level of diversification to minimize the risk of large losses in a single asset class. Accordingly, plan assets for the postretirement health care and life insurance benefit plan do not have a concentration of assets in a single entity, industry, commodity or class of investment fund.
Recently Issued Accounting Standards	In April 2014, the Financial Accounting Standards Board issued Accounting Standards Update (ASU) No. 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity. This update defines a discontinued operation as a disposal of a component or a group of components that is disposed of or is classified as held for sale and represents a strategic shift that has (or will have) a major effect on an entity’s operations and financial results. The amendment is effective for all annual periods beginning on or after December 15, 2014, and interim periods within those annual periods. Energen does not expect the adoption of this ASU to have a material impact on its consolidated financial statements.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Derivative Instruments, Gain (Loss)	We further reclassified all commodity hedges from oil and natural gas operating revenues to gain (loss) on derivative instruments, net, as follows:



	Years ended December 31, (in thousands)	2014			2013			2012
	Open non-cash mark-to-market gains (losses) on derivative instruments	$	315,445		$	(47,832	)	$	58,750

	Closed gains (losses) on derivative instruments	19,574			(2,192		)	25,403

	Gain (loss) on derivative instruments, net	$	335,019		$	(50,024	)	$	84,153

Schedule of Discontinued Operations	The table below provides a detail of these items included in income (loss) from discontinued operations as follows:



	Years ended December 31, (in thousands)	2014			2013			2012
	Alagasco net income	$	40,646		$	57,399		$	49,402

	Depreciation, depletion and amortization	(408		)	(598		)	(572		)
	General and administrative	3,337			5,894			5,166

	Interest expense	(17,306		)	(13,815		)	(1,693		)
	Other income	(347		)	(1,342		)	(977		)
	Income tax expense (benefit)	5,567			3,728			(727		)

	Alagasco income from discontinued operations	31,489			51,266			50,599

	Energen income (loss) from discontinued operations	(2,197		)	7,813			(1,658		)

	Income from discontinued operations	$	29,292		$	59,079		$	48,941

	As discussed in Note 14, Acquisition and Disposition of Properties, and above, the following tables detail held for sale properties by major classes of assets and liabilities:



	(in thousands)	31-Dec-14
					San Juan Basin*
	Oil and natural gas properties				$	1,166,124

	Less accumulated depreciation, depletion and amortization				(770,327		)
	Total assets held for sale				395,797

	Other long-term liabilities				(24,230		)
	Total liabilities held for sale				(24,230		)

	Total net assets held for sale				$	371,567

	*The San Juan Basin natural gas assets which are held for sale as of December 31, 2014, do not qualify for discontinued operations as we will have ongoing operations in the San Juan Basin.


	(in thousands)	31-Dec-13
		Alabama Gas Corporation			Black Warrior Basin			North Louisiana/East Texas			Total
	Cash	$	3,032		$	—		$	—		$	3,032

	Accounts receivable*	103,748			2,829			1,272			107,849

	Inventories	41,200			—			68			41,268

	Oil and natural gas properties	—			—			348,379			348,379

	Less accumulated depreciation, depletion and amortization	—						(301,609		)	(301,609		)

	Utility plant	1,491,433			—			—			1,491,433

	Less accumulated depreciation	(605,924		)	—			—			(605,924		)

	Other property, net	41			—			165			206

	Other current assets*	29,458			—			—			29,458

	Other long-term assets	128,780			—			—			128,780

	Total assets held for sale	1,191,768			2,829			48,275			1,242,872

	Accounts payable	(48,653		)	(1,732		)	(11		)	(50,396		)
Royalty payable	—			(550		)	(869		)	(1,419		)

Accrued taxes	(28,027		)	—			—			(28,027		)

Notes payable to banks	(50,000		)	—			—			(50,000		)

Other current liabilities*	(105,013		)	(379		)	(21		)	(105,413		)
Other long-term liabilities	(331,409		)	—			(14,983		)	(346,392		)

Long-term debt	(249,923		)	—			—			(249,923		)

Total liabilities held for sale	(813,025		)	(2,661		)	(15,884		)	(831,570		)
Total net assets held for sale	$	378,743		$	168		$	32,391		$	411,302

*At December 31, 2013, Alagasco’s accounts receivable included a consolidating adjustment of $4.7 million to adjust for affiliated companies receivables. Certain other current assets and other current liabilities at Alagasco of $1.6 million and $0.5 million, respectively, were reclassified to continuing operations at Energen.


Years ended December 31, (in thousands, except per share data)	2014			2013			2012
Natural gas distribution revenues	$	397,648		$	533,338		$	451,589

Oil and natural gas revenues	5,199			60,191			76,350

Total revenues	$	402,847		$	593,529		$	527,939

Pretax income from discontinued operations	$	47,220		$	92,253		$	79,197

Income tax expense	17,928			33,174			30,256

Income From Discontinued Operations	$	29,292		$	59,079		$	48,941

Gain on disposal of discontinued operations, net	$	724,594		$	5,605		$	—

Income tax expense	285,497			2,011			—

Gain on Disposal of Discontinued Operations, net	$	439,097		$	3,594		$	—

Total Income From Discontinued Operations	$	468,389		$	62,673		$	48,941

Diluted Earnings Per Average Common Share
Income from discontinued operations	$	0.4		$	0.81		$	0.68

Gain on disposal of discontinued operations, net	5.99			0.05			—

Total Income From Discontinued Operations	$	6.39		$	0.86		$	0.68

Basic Earnings Per Average Common Share
Income from discontinued operations	$	0.4		$	0.82		$	0.68

Gain on disposal of discontinued operations, net	6.02			0.05			—

Total Income From Discontinued Operations	$	6.42		$	0.87		$	0.68

LongTerm_Debt_and_Notes_Payabl1

Long-Term Debt and Notes Payable (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Schedule of Long-Term Debt	Long-term debt consisted of the following:



	(in thousands)	December 31, 2014			December 31, 2013
	Credit facility	$	485,000		$	—

	7.40% Medium-term Notes, Series A, due July 24, 2017	2,000			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			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

	Senior Term Loans, (floating rate interest LIBOR plus 1.625%)	—			600,000

	Total	1,039,000			1,154,000

	Less amounts due within one year	—			60,000

	Less unamortized debt discount	437			459

	Total	$	1,038,563		$	1,093,541

Schedule of Aggregate Maturities of Long-Term Debt	The aggregate maturities of Energen’s long-term debt as of December 31, 2014 are as follows:



	Years ending December 31, (in thousands)
	2015	2016	2017	2018	2019	Thereafter
	$—	$—	$19,000	$—	$485,000	$535,000
Schedule of Credit Facilities	The following is a summary of information relating to Energen’s credit facilities:



	(in thousands)	December 31, 2014			December 31, 2013
	Notes payable to banks	$	485,000		$	489,000

	Available for borrowings	1,515,000			761,000

	Total	$	2,000,000		$	1,250,000

	Maximum amount outstanding at any month-end	$	750,000		$	859,000

	Average daily amount outstanding	$	482,166		$	772,012

	Weighted average interest rates based on:
	Average daily amount outstanding	1.46		%	1.39		%
	Amount outstanding at year-end	1.67		%	1.4		%

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Schedule of Components of Income Taxes	The components of Energen’s income taxes consisted of the following:



	Years ended December 31, (in thousands)	2014			2013			2012
	Taxes estimated to be payable currently:
	Federal	$	161,576		$	23,342		$	16,295

	State	72,379			2,516			3,125

	Total current	233,955			25,858			19,420

	Taxes deferred:
	Federal	144,645			85,950			119,053

	State	(34,447		)	(2,300		)	5,346

	Total deferred	110,198			83,650			124,399

	Total income tax expense	$	344,153		$	109,508		$	143,819

Schedule of Components of Income Tax Expense (Benefit), Continuing and Discontinued Operations	The components of Energen’s income taxes consisted of the following:



	Years ended December 31, (in thousands)	2014			2013			2012
	Income tax expense from continuing operations	$	40,728		$	74,323		$	113,563

	Income tax expense from discontinued operations	17,928			33,174			30,256

	Income tax expense from gain on disposal of discontinued operations	285,497			2,011			—

	Total income tax expense	$	344,153		$	109,508		$	143,819

Schedule of Deferred Tax Assets and Liabilities	Temporary differences and carryforwards which gave rise to Energen’s deferred tax assets and liabilities were as follows:



	(in thousands)	December 31, 2014						December 31, 2013
		Current			Noncurrent			Current			Noncurrent
	Deferred tax assets:
	Minimum tax credit	$	—		$	46,338		$	—		$	—

	Allowance for doubtful accounts	244			—			251			—

	Insurance and other accruals	2,537			—			3,082			—

	Compensation accruals	11,355			—			12,925			—

	Pension and other costs	—			7,009			—			3,652

	Other comprehensive income	10,732			1,581			—			15,350

	Derivative instruments	—			—			10,769			—

	State net operating losses and other carryforwards	—			15,392			—			4,577

	Other	665			—			235			—

	Total deferred tax assets	25,533			70,320			27,262			23,579

	Valuation allowance	(1,122		)	(2,467		)	(299		)	(2,674		)
	Total deferred tax assets	24,411			67,853			26,963			20,905




	Deferred tax liabilities:
	Depreciation and basis differences	—			1,057,430			—			821,425

	Derivative instruments	102,691			—			—			2,048

	Other comprehensive income	—			—			5,540			—

	Other	884			10,909			173			5,046

	Total deferred tax liabilities	103,575			1,068,339			5,713			828,519

	Net deferred tax assets (liabilities)	$	(79,164	)	$	(1,000,486	)	$	21,250		$	(807,614	)

Schedule of Effective Income Tax Rate Reconciliation	Total income tax expense from continuing operations differed from the amount which would have been provided by applying the statutory federal income tax rate of 35 percent to earnings before taxes as illustrated below:



	Years ended December 31, (in thousands)	2014			2013			2012
	Income tax expense at statutory federal income tax rate	$	49,130		$	75,671		$	111,364

	Increase (decrease) resulting from:
	State income taxes, net of federal income tax benefit	93			1,461			2,423

	Impact of state law changes	(121		)	(1,966		)	—

	Impact of state deferred tax revaluation on San Juan properties	(8,382		)	—			—

	401(k) stock dividend deduction	(232		)	(449		)	(514		)
	Other, net	240			(394		)	290

	Total income tax expense	$	40,728		$	74,323		$	113,563

	Effective income tax rate (%)	29.01			34.38			35.69

Schedule of Reconciliation of Unrecognized Tax Benefits	A reconciliation of Energen’s beginning and ending amount of unrecognized tax benefits is as follows:



	(in thousands)
	Balance as of December 31, 2011	$	10,593

	Additions based on tax positions related to the current year	3,731

	Additions for tax positions of prior years	269

	Reductions for tax positions of prior years	(446		)
	Lapse of statute of limitations	(1,592		)
	Balance as of December 31, 2012	12,555

	Additions based on tax positions related to the current year	4,546

	Additions for tax positions of prior years	366

	Reductions for tax positions of prior years	(46		)
	Lapse of statute of limitations	(1,435		)
	Balance as of December 31, 2013	15,986

	Additions based on tax positions related to the current year	3,873

	Additions for tax positions of prior years	19

	Reductions for tax positions of prior years	(954		)
	Lapse of statute of limitations	(1,394		)
	Balance as of December 31, 2014	$	17,530

Employee_Benefit_Plans_Tables

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Schedule of benefit obligations	The following table sets forth the combined funded status of the defined qualified and nonqualified supplemental benefit plans along with the postretirement health care and life insurance benefit plans and their reconciliation with the related amounts in Energen’s consolidated financial statements. As Energen has frozen and plans to terminate the defined benefit pension plan, the projected pension benefit obligation as of December 31, 2014 represents the present value of the estimated cost of settling the plans benefit obligation. The amounts in the table below as of December, 31 2013 include both Energen and Alagasco, except for Alagasco plans which contain certain labor union agreements:



	As of December 31, (in thousands)	2014			2013			2014			2013
		Pension						Postretirement Benefits
	Accumulated benefit obligation	$	107,669		$	225,969

	Benefit obligation:
	Balance at beginning of period	$	266,294		$	293,075		$	33,224		$	46,901

	Service cost	8,329			13,293			262			1,125

	Interest cost	5,325			10,161			716			1,931

	Actuarial (gain) loss	9,078			(26,909		)	6,385			(13,311		)

	Curtailment gain	(8,496		)	(4,223		)	—			(1,255		)

	Transfer in connection with the sale of Alagasco	(124,783		)	—			(28,648		)	—

	Termination benefit charge	2,477			—			—			—

	Retiree drug subsidy program	—			—			48			124

	Benefits paid	(50,555		)	(19,103		)	(860		)	(2,291		)
	Balance at end of period	$	107,669		$	266,294		$	11,127		$	33,224

	Plan assets:
	Fair value of plan assets at beginning of period	$	193,457		$	182,796		$	55,459		$	48,194

	Actual return (loss) on plan assets	5,359			19,595			(331		)	8,072

	Employer contributions	19,164			10,169			21			1,484

	Transfer in connection with the sale of Alagasco	(99,883		)	—			(43,596		)	—

	Benefits paid	(50,555		)	(19,103		)	(860		)	(2,291		)
	Fair value of plan assets at end of period	$	67,542		$	193,457		$	10,693		$	55,459


	Funded status of plans	$	(40,127	)	$	(72,837	)	$	(434	)	$	22,235



	Noncurrent assets	$	—		$	—		$	—		$	8,894

	Noncurrent assets in assets held for sale	—			—			—			13,341

	Current liabilities	(24,626		)	(6,145		)	—			—

	Noncurrent liabilities	(15,501		)	(47,485		)	(434		)	—

	Noncurrent liabilities in liabilities related to assets held for sale	—			(19,207		)	—			—

	Net asset (liability) recognized	$	(40,127	)	$	(72,837	)	$	(434	)	$	22,235

	Amounts recognized to accumulated other comprehensive income:
	Prior service costs, net of taxes	$	—		$	323		$	—		$	—

	Net actuarial (gain) loss, net of taxes	22,246			37,479			624			(5,584		)

	Transition obligation, net of taxes	—			—			—			27

Total accumulated other comprehensive income (loss)	$	22,246		$	37,802		$	624		$	(5,557	)

Schedule of allocation of plan assets	The Company’s weighted average plan asset allocations by asset category were as follows:



		Pension						Postretirement Benefits
	As of December 31,	Target		2014		2013		Target		2014		2013
	Asset category:
	Equity securities	—	%	—	%	34	%	60	%	60	%	61	%
	Debt securities	—	%	—	%	28	%	40	%	40	%	39	%
	Other	100	%	100	%	38	%	—	%	—	%	—	%
	Total	100	%	100	%	100	%	100	%	100	%	100	%
Schedule of net periodic benefit cost	The components of net periodic benefit cost from continuing operations were as follows:



	Years ended December 31, (in thousands)	2014			2013			2012
	Pension Plans
	Components of net periodic benefit cost:
	Service cost	$	6,808		$	5,196		$	4,023

	Interest cost	4,498			4,496			4,296

	Expected long-term return on assets	(4,386		)	(5,225		)	(5,134		)
	Prior service cost amortization	202			246			209

	Actuarial loss amortization	4,995			6,919			3,945

	Termination benefit charge	2,477			—			—

	Settlement charge	4,082			161			—

	Curtailment expense (gain)	254			(4		)	—

	Net periodic expense	$	18,930		$	11,789		$	7,339

	Postretirement Benefit Plans
	Components of net periodic benefit cost:
	Service cost	$	253		$	386		$	454

	Interest cost	661			645			810

	Expected long-term return on assets	(1,122		)	(787		)	(741		)
	Actuarial gain amortization	(653		)	(28		)	—

	Transition obligation amortization	44			229			248

	Net periodic (income) expense	$	(817	)	$	445		$	771

Schedule of other changes in plan assets and projected benefit obligations recognized in other comprehensive income	Other changes in plan assets and projected benefit obligations recognized in other comprehensive income were as follows:



	Years ended December 31, (in thousands)	2014			2013			2012
	Pension Plans
	Net actuarial (gain) loss experienced during the year	$	10,495		$	(14,138	)	$	28,748

	Net actuarial loss recognized as expense	(25,433		)	(8,934		)	(4,908		)
	Prior service cost recognized as expense	(246		)	(311		)	(340		)
	Curtailment loss	(8,749		)	—			—

	Total recognized in other comprehensive income (loss)	(23,933		)	(23,383		)	23,500

	Postretirement Benefit Plans
	Net actuarial (gain) loss experienced during the year	$	7,649		$	(8,057	)	$	(1,787	)

	Net actuarial gain recognized as expense	1,908			550			—

	Transition obligation recognized as expense	(48		)	(283		)	(294		)
	Total recognized in other comprehensive income (loss)	$	9,509		$	(7,790	)	$	(2,081	)

Schedule of estimated amount to be amortized from accumulated other comprehensive income	Estimated amounts to be amortized from accumulated other comprehensive income into pension cost during 2015 are included in the table below. In addition, the Company anticipates recognizing the remaining amounts from accumulated other comprehensive income on the date of distribution of pension plan benefits.



	(in thousands)
	Amortization of net actuarial loss	$	841


Schedule of weighted average rate assumptions	The weighted average rate assumptions to determine net periodic benefit costs were as follows:



	Years ended December 31,	2014		2013		2012
	Pension Plans
	Discount rate	3.66	%	3.63	%	4.52	%
	Expected long-term return on plan assets	7	%	7	%	7	%
	Rate of compensation increase for pay-related plans	3.63	%	3.71	%	3.59	%
	Postretirement Benefit Plans
	Discount rate	4.88	%	4.36	%	4.95	%
	Expected long-term return on plan assets	7	%	7	%	7	%
	Rate of compensation increase	3.6	%	3.7	%	3.55	%

	The pension benefit obligation as of December 31, 2014 represents the present value of the estimated cost of settling the benefit obligation of the plan. For our defined benefit pension plan, we discounted the estimated termination liability using the one year spot rate of 0.70 percent. The discount rate shown below represents the weighted average for both the defined qualified and nonqualified supplemental benefit plans. As the plans were frozen as of December 31, 2014, the rate of compensation increase no longer applies for any of the plans. The weighted average assumptions used to determine the benefit obligations at the measurement date were as follows:



	Years ended December 31,	2014		2013
	Pension Plans
	Discount rate	0.96	%	4.29	%
	Rate of compensation increase for pay-related plans	—	%	3.63	%
	Postretirement Benefit Plans
	Discount rate	4.25	%	4.95	%
	Rate of compensation increase for pay-related plans	—	%	3.6	%
Schedule of assumed post-65 health care cost rend rates	The assumed post-65 health care cost trend rates used to determine the postretirement benefit obligation at the measurement date were as follows:



	As of December 31,	2014		2013
	Health care cost trend rate assumed for next year	7.25	%	6.5	%
	Rate to which the cost trend rate is assumed to decline	5	%	5	%
	Year that rate reaches ultimate rate	2021		2020

Schedule of effect of 1 percentage point change in assumed health care cost trend rates	accumulated postretirement benefit obligation due to the separation of assets and obligations of the postretirement healthcare and life insurance benefit plan into an Energen and an Alagasco plan. Employees remaining at Energen will receive a fixed postretirement benefit.
Schedule of expected benefit payments	The following benefit payments, which reflect expected future service, as appropriate, are anticipated to be paid as follows:



	(in thousands)	Pension Benefits	Postretirement Benefits
	2015	$92,711	$324
	2016	$14,601	$397
	2017	$113	$472
	2018	$110	$541
	2019	$107	$583
	2020-2024	$484	$3,266
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Schedule of allocation of plan assets	Plan assets included in the funded status of the pension plans were as follows:


		31-Dec-14
	(in thousands)	Level 1			Level 2			Total
	Cash and cash equivalents	$	67,542		$	—		$	67,542

	Total	$	67,542		$	—		$	67,542




		December 31, 2013
	(in thousands)	Level 1			Level 2			Total
	United States equities	$	34,117		$	—		$	34,117

	Global equities	20,144			8,636			28,780

	Fixed income	—			50,777			50,777

	Alternative investments	—			37,292			37,292

	Cash and cash equivalents	5,970			36,521			42,491

	Total	$	60,231		$	133,226		$	193,457

Schedule of reconciliation of plan assets in Level 3 of fair value hierarchy	The following is a reconciliation of plan assets in Level 3 of the fair value hierarchy:



	Years ended December 31, (in thousands)	2013			2012
	Balance at beginning of period	$	14,500		$	17,399

	Unrealized gains (losses)	—			992

	Unrealized gains relating to instruments held at the reporting date	—			242

	Settlements	—			(4,948		)

	Purchases	—			815

	Transfer out of Level 3	(14,500		)	—

	Balance at end of period	$	—		$	14,500

Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Schedule of allocation of plan assets	Plan assets included in the funded status of the postretirement benefit plans were as follows:



		December 31, 2014
	(in thousands)	Level 1			Level 2			Total
	United States equities	$	4,715		$	—		$	4,715

	Global equities	1,711			—			1,711

	Fixed income	—			4,267			4,267

	Total	$	6,426		$	4,267		$	10,693




		December 31, 2013
	(in thousands)	Level 1			Level 2			Total
	United States equities	$	24,152		$	—		$	24,152

	Global equities	9,563			—			9,563

	Fixed income	—			21,744			21,744

	Total	$	33,715		$	21,744		$	55,459

Nonqualified Supplemental Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Schedule of allocation of plan assets	Other investment assets designated for payment of the nonqualified supplemental retirement plans were as follows:



		December 31, 2014
	(in thousands)	Level 1			Level 2			Total
	Fixed income	$	—		$	4,255		$	4,255

	Cash and cash equivalents	9,929			—			9,929

	Total	$	9,929		$	4,255		$	14,184




		December 31, 2013
	(in thousands)	Level 1			Level 2			Total
	Insurance contracts	$	—		$	14,805		$	14,805

	United States equities	5,579			—			5,579

	Global equities	2,338			—			2,338

	Fixed income	—			11,039			11,039

	Total	$	7,917		$	25,844		$	33,761

Schedule of reconciliation of plan assets in Level 3 of fair value hierarchy	The following is a reconciliation of insurance contracts in Level 3 of the fair value hierarchy:



	Years ended December 31, (in thousands)	2013			2012
	Balance at beginning of period	$	5,600		$	5,332

	Unrealized gains relating to instruments held at the reporting date	—			268

	Transfer out of Level 3	(5,600		)	—

	Balance at end of period	$	—		$	5,600

Common_Stock_Plans_Tables

Common Stock Plans (Tables)	12 Months Ended
	Dec. 31, 2014
Share-based Compensation [Abstract]
Schedule of Performance Share Award Activity	No performance share awards were granted in 2012. A summary of performance share award activity as of December 31, 2014, and transactions during the years ended December 31, 2014 and 2013 is presented below:



		Stock Incentive Plan
		Shares		Weighted
				Average Price

	Nonvested at December 31, 2012	—		$	—

	Granted (two-year vesting period)	86,221		61.14

	Granted (three-year vesting period)	82,606		62.96

	Forfeited	(8,008	)	60.03

	Nonvested at December 31, 2013	160,819		62.13

	Granted (two-year vesting period)	937		131.56

	Granted (three-year vesting period)	65,309		93.49

	Vested and paid	(14,097	)	70.06

	Nonvested at December 31, 2014	212,968		$	71.53

Schedule of Stock Option Activity and Transactions	A summary of stock option activity as of December 31, 2014, and transactions during the years ended December 31, 2014, 2013 and 2012 are presented below:



		Stock Incentive Plan
		Shares		Weighted Average Exercise Price


	Outstanding at December 31, 2011	1,338,241		$	44.77

	Granted	371,040		54.11

	Exercised	(58,471	)	24.55

	Forfeited	(2,335	)	46.45

	Outstanding at December 31, 2012	1,648,475		47.58

	Granted	137,762		49.22

	Exercised	(590,119	)	40.92

	Forfeited	(5,074	)	51.85

	Outstanding at December 31, 2013	1,191,044		51.06

	Granted	110,307		72.55

	Exercised	(544,280	)	50.09

	Outstanding at December 31, 2014	757,071		$	54.88

	Exercisable at December 31, 2012	987,733		$	43.75

	Exercisable at December 31, 2013	713,445		$	49.8

	Exercisable at December 31, 2014	454,938		$	51.88

	Remaining reserved for issuance at December 31, 2014	2,635,544		—

Schedule of Stock Options Valuation Assumptions	Energen uses the Black-Scholes pricing model to calculate the fair values of the options awarded. For purposes of this valuation the following assumptions were used to derive the fair values:



	Grant date	4/15/14	1/22/14	10/15/13	1/24/13		1/25/12
	Awards granted	2,439	107,868	3,686	134,076		371,040

	Fair market value of stock option at grant	$32.22	$27.57	$30.53	$16.66		$18.79
	Expected life of award	5.8 years	5.8 years	5.8 years	5.8 years		5.8 years

	Risk-free interest rate	1.93%	2.06%	1.79%	1.01	%	1.07	%
	Annualized volatility rate	40.70%	40.70%	40.60%	40.3	%	39.6	%
	Dividend yield	0.20%	0.80%	0.70%	1.2	%	1	%
Schedule of Outstanding Stock Options by Range of Exercise Prices	The following table summarizes options outstanding as of December 31, 2014:



	Stock Incentive Plan
	Range of Exercise Prices	Shares	Weighted Average Remaining Contractual Life
	$46.45	25,470	2.00 years
	$60.56	48,560	3.00 years
	$29.79	35,161	4.00 years
	$46.69	26,481	5.00 years
	$54.99	111,487	6.00 years
	$54.11	271,848	7.00 years
	$48.36	124,071	8.00 years
	$80.48	3,686	8.79 years
	$72.39	107,868	9.00 years
	$79.63	2,439	9.00 years
	$29.79-$80.48	757,071	6.68 years
Schedule of Restricted Stock Activity and Transactions	A summary of restricted stock unit activity as of December 31, 2014, and transactions during the years ended December 31, 2014, 2013 and 2012 is presented below:



		Stock Incentive Plan
		Shares		Weighted Average Price
	Nonvested at December 31, 2011	9,275		$	42.99

	Granted	11,115		45.24

	Vested	(9,275	)	42.97

	Nonvested at December 31, 2012	11,115		45.24

	Granted	52,650		52.34

	Forfeited	(1,247	)	48.36

	Nonvested at December 31, 2013	62,518		51.16

	Granted	48,904		71.91

	Vested	(11,848	)	65.94

	Nonvested at December 31, 2014	99,574		$	59.6

Summary of Stock Appreciation Rights Activity	A summary of stock appreciation rights activity as of December 31, 2014, and transactions during the years ended December 31, 2014, 2013 and 2012 are presented below:



		Stock Appreciation Rights Plan
		Shares		Weighted Average Exercise Price


	Outstanding at December 31, 2011	777,218		$	42

	Exercised/forfeited	(124,188	)	30.9

	Outstanding at December 31, 2012	653,030		44.14

	Granted	88,000		48.36

	Exercised/forfeited	(363,653	)	39.66

	Outstanding at December 31, 2013	377,377		49.48

	Granted	62,749		72.39

	Exercised/forfeited	(164,976	)	52.37

	Outstanding at December 31, 2014	275,150		$	52.96

Schedule of Stock Appreciation Rights Valuation Assumptions	For purposes of this valuation the following assumptions were used to derive the fair values as of December 31, 2014:



	Grant date	1/22/14	1/24/13	1/24/13	1/26/11	1/26/11
				(modified)		(modified)
	Awards granted	62,749	87,069	931	182,199	7,785
	Fair market value of award	$18.63	$25.93	$20.14	$19.15	$16.27
	Expected life of award	5.56 years	4.57 years	2.0 years	3.04 years	2.0 years
	Risk-free interest rate	1.77%	1.57%	0.65%	1.12%	0.65%
	Annualized volatility rate	33.40%	33.40%	33.40%	33.40%	33.40%
	Dividend yield	0.13%	0.13%	0.13%	0.13%	0.13%



	Grant date	1/27/10	2/13-16/2009	1/28/09	2/4/08	2/1/07
	Awards granted	171,749	3,292	305,257	67,093	85,906
	Fair market value of award	$22.50	$33.23	$34.66	$10.57	$19.25
	Expected life of award	2.54 years	2.04 years	2.04 years	1.55 years	1.04 years
	Risk-free interest rate	0.90%	0.67%	0.67%	0.45%	0.26%
	Annualized volatility rate	33.40%	33.40%	33.40%	33.40%	33.40%
	Dividend yield	0.13%	0.13%	0.13%	0.13%	0.13%
Schedule of Incentive Units Activity	A summary of Petrotech unit activity as of December 31, 2014, and transactions during the years ended December 31, 2014, 2013 and 2012 are presented below:



			Petrotech Incentive Plan
			Shares


	Outstanding at December 31, 2011		11,061
	Granted (three-year vesting period)		102,349

	Granted (two-year vesting period)		3,768

	Granted (18 month vesting period)		40,822

	Paid		(3,281	)
	Forfeited		(13,476	)
	Outstanding at December 31, 2012		141,243

	Granted (three-year vesting period)		92,418

	Granted (17 month vesting period)		2,952

	Paid		(36,792	)
	Forfeited		(26,529	)
	Outstanding at December 31, 2013		173,292

	Granted		76,084
	Paid		(4,431	)
	Forfeited		(31,075	)
	Outstanding at December 31, 2014		213,870

Derivative_Commodity_Instrumen1

Derivative Commodity Instruments (Tables)	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Liabilities at Fair Value	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)	31-Dec-14
											Gross Amounts Not Offset in the Balance Sheets
		Gross Amounts Recognized at Fair Value			Gross Amounts Offset in the Balance Sheets			Net Amount 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	$	339,977		$	(17,640	)	$	322,337		$	—	$	—	$	322,337

	Noncurrent derivative instruments	—			—			—			—		—		—

	Total derivative assets	339,977			(17,640		)	322,337			—		—		322,337

	Liabilities
	Derivative instruments	18,628			(17,640		)	988			—		—		988

	Noncurrent derivative instruments	—			—			—			—		—		—

	Total derivative liabilities	18,628			(17,640		)	988			—		—		988

	Total derivatives	$	321,349		$	—		$	321,349		$	—	$	—	$	321,349




	(in thousands)	31-Dec-13
											Gross Amounts Not Offset in the Balance Sheets
		Gross Amounts Recognized at Fair Value			Gross Amounts Offset in the Balance Sheets			Net Amount 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	$	36,223		$	(18,760	)	$	17,463		$	—	$	—	$	17,463

	Noncurrent derivative instruments	7,992			(2,553		)	5,439			—		—		5,439

	Total derivative assets	44,215			(21,313		)	22,902			—		—		22,902

	Liabilities
	Derivative instruments	49,062			(18,760		)	30,302			—		—		30,302

	Noncurrent derivative instruments	2,553			(2,553		)	—			—		—		—

	Total derivative liabilities	51,615			(21,313		)	30,302			—		—		30,302

	Total derivatives	$	(7,400	)	$	—		$	(7,400	)	$	—	$	—	$	(7,400	)

	The following fair value hierarchy tables present information about Energen’s assets and liabilities measured at fair value on a recurring basis:



		December 31, 2014
	(in thousands)	Level 2			Level 3			Total
	Assets
	Derivative instruments	$	294,865		$	27,472		$	322,337

	Total assets	294,865			27,472			322,337

	Liabilities
	Derivative instruments	2,048			(3,036		)	(988		)

	Total liabilities	2,048			(3,036		)	(988		)

	Net derivative asset	$	296,913		$	24,436		$	321,349




	December 31, 2013
(in thousands)	Level 2			Level 3			Total
Assets
Derivative instruments	$	(1,658	)	$	19,121		$	17,463

Noncurrent derivative instruments	4,383			1,056			5,439

Total assets	2,725			20,177			22,902

Liabilities
Derivative instruments	(28,414		)	(1,888		)	(30,302		)
Total liabilities	(28,414		)	(1,888		)	(30,302		)
Net derivative asset (liability)	$	(25,689	)	$	18,289		$	(7,400	)

Schedule of Cash Flow Hedging Instruments, Statements of Financial Performance and Financial Position, Location	The following table details the effect of derivative commodity instruments in cash flow hedging relationships on the financial statements:



	Years ended December 31, (in thousands)	Location on Statements of Income	2014			2013			2012
	Net gain (loss) recognized in other comprehensive income on derivatives (effective portion), net of tax of $23, ($6,660) and $40,720	—	$	37		$	(10,866	)	$	66,438

	Gain reclassified from accumulated other comprehensive income into income (effective portion)	Gain (loss) on derivative instruments, net	$	21,612		$	34,293		$	52,694

	Gain (loss) recognized in income on derivatives (ineffective portion and amount excluded from effectiveness testing)	Gain (loss) on derivative instruments, net	$	—		$	835		$	(5,340	)

Schedule of Other Derivatives Not Designated as Hedging Instruments, Statements of Financial Performance and Financial Position, Location	The following table details the effect of open and closed derivative commodity instruments not designated as hedging instruments on the income statement:



	Years ended December 31, (in thousands)	Location on Statements of Income	2014			2013			2012
	Gain (loss) recognized in income on derivative	Gain (loss) on derivative instruments, net	$	313,408		$	(73,980	)	$	61,841

Schedule of Hedging Transactions	As of December 31, 2014, Energen entered into the following transactions for 2015 and subsequent years:



	Production Period	Total Hedged Volumes		Average Contract	Description
				Price
	Oil
	2015	8,280	MBbl	$89.30 Bbl	NYMEX Swaps
	Oil Basis Differential
	2015	2,160	MBbl	$(4.30) Bbl	WTS/WTI Basis Swaps*
	2015	6,840	MBbl	$(4.82) Bbl	WTI/WTI Basis Swaps**
	Natural Gas
	2015	23	Bcf	$4.13 Mcf	Basin Specific Swaps - San Juan
	2015	8	Bcf	$4.25 Mcf	Basin Specific Swaps - Permian
	*WTS - West Texas Sour/Midland, WTI - West Texas Intermediate/Cushing
	**WTI - West Texas Intermediate/Midland, WTI - West Texas Intermediate/Cushing

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Schedule of Changes in Fair Value of Derivative Instruments Classified as Level 3	The table below sets forth a summary of changes in the fair value of Energen’s Level 3 derivative commodity instruments as follows:



	Years ended December 31, (in thousands)	2014			2013			2012
	Balance at beginning of period	$	18,289		$	89,019		$	65,801

	Realized gains	22,208			55,210			63,720

	Unrealized gains (losses) relating to instruments held at the reporting date*	2,981			(71,367		)	22,160

	Settlements during period	(19,042		)	(54,573		)	(62,662		)
	Balance at end of period**	$	24,436		$	18,289		$	89,019

	*Includes $20.2 million in mark-to-market gains, $7.6 million in mark-to-market losses and $19.9 million in mark-to-market gains for the years ended December 31, 2014, 2013 and 2012, respectively.
	**Included in the Level 3 fair value at December 31, 2014 are gains of $3.2 million from natural gas liquids and Gas Daily contracts which were closed at December 31, 2014 but not cash settled.
Schedule of Level Three Fair Value Measurements of Derivative Commodity Instruments	The tables below set 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 December 31, 2014			Valuation Technique*	Unobservable Input*	Range
	Oil Basis - WTS/WTI
	2015	$	(3,836	)	Discounted Cash Flow	Forward Basis	($2.55 - $2.66) Bbl
	Oil Basis - WTI/WTI
	2015	$	(14,419	)	Discounted Cash Flow	Forward Basis	($2.72 - $2.82) Bbl
	Natural Gas Basis - San Juan
	2015	$	28,597		Discounted Cash Flow	Forward Basis	($0.13- $0.14) Mcf

	Natural Gas Basis - Permian
	2015	$	10,927		Discounted Cash Flow	Forward Basis	($0.15) Mcf

	*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.

Exploratory_Costs_Tables

Exploratory Costs (Tables)	12 Months Ended
	Dec. 31, 2014
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:



	Years ended December 31, (in thousands)	2014			2013			2012
	Capitalized exploratory well costs at beginning of period	$	57,600		$	79,791		$	70,437

	Additions pending determination of proved reserves	946,751			421,599			406,226

	Reclassifications due to determination of proved reserves	(882,254		)	(442,909		)	(396,872		)
	Exploratory well costs charged to expense	(2,658		)	(881		)	—

	Capitalized exploratory well costs at end of period	$	119,439		$	57,600		$	79,791


	The following table sets forth capitalized exploratory wells costs and includes amounts capitalized for a period greater than one year:



	(in thousands)	31-Dec-14			31-Dec-13
	Exploratory wells in progress	$	18,781		$	14,794

	Capitalized exploratory well costs for a period of one year or less	100,658			42,481

	Capitalized exploratory well costs for a period greater than one year	—			1,206

	Total capitalized exploratory well costs	$	119,439		$	58,481

Reconciliation_of_Earnings_Per1

Reconciliation of Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Schedule of Earnings Per Share Reconciliation

	Years ended December 31,
	(in thousands, except per share amounts)				2014						2013					2012
		Net			Shares		Per Share Amount		Net		Shares	Per Share Amount		Net		Shares	Per Share Amount
		Income							Income					Income
	Basic EPS	$	568,032		72,897		$	7.79	$	204,554	72,318	$	2.83	$	253,562	72,119	$	3.52

	Effect of dilutive securities
	Stock options				216						112					196

	Non-vested restricted stock				58						20					1

	Performance share awards				104						21					—

	Diluted EPS	$	568,032		73,275		$	7.75	$	204,554	72,471	$	2.82	$	253,562	72,316	$	3.51

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	Energen had the following shares that were excluded from the computation of diluted EPS, as inclusion would be anti-dilutive.



	Years ended December 31, (in thousands)	2014		2013		2012
	Stock options	114		134		850

	Non-vested restricted stock	3		7		—

	Performance share awards	2		4		—

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Schedule of Minimum Future Rental Payments	Minimum future rental payments required after 2014 under leases with initial or remaining noncancelable lease terms in excess of one year are as follows:



	Years Ending December 31, (in thousands)
	2015	2016	2017	2018	2019	2020 and thereafter
	$2,698	$2,676	$2,468	$2,429	$2,326	$—

Asset_Retirement_Obligations_T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]
Schedule of Change in Asset Retirement Obligation	The following table reflects the components of the change in Energen’s ARO balance:



	(in thousands)
	Balance as of December 31, 2011	$	107,340

	Liabilities incurred	3,994

	Liabilities settled	(845		)
	Accretion expense (including discontinued operations of $1,195)	7,534

	Balance as of December 31, 2012	118,023

	Liabilities incurred	2,772

	Liabilities settled	(5,525		)
	Accretion expense (including discontinued operations of $1,197)	8,192

	Reclassification associated with held for sale properties*	(14,929		)
	Balance as of December 31, 2013	108,533

	Liabilities incurred	2,266

	Liabilities settled	(1,543		)
	Accretion expense (including discontinued operations of $251)	7,859

	Revision in estimated cash flows	692

	Reclassification associated with held for sale properties**	(23,747		)
	Balance as of December 31, 2014	$	94,060

	*Asset retirement obligation associated with North Louisiana/East Texas properties are included as liabilities related to assets held for sale in current liabilities on the balance sheet.
	**Asset retirement obligation associated with certain San Juan Basin properties are included as liabilities related to assets held for sale in current liabilities on the balance sheet.

Asset_Impairment_Tables

Asset Impairment (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Impairment of Long-Lived Assets Held and Used by Asset	Impairments recognized by Energen during the years ended December 31, 2014, 2013 and 2012 are presented below:



	Years ended December 31, (in thousands)	2014		2013		2012
	Continuing operations
	Permian Basin oil properties	$	125,693	$	—	$	—

	Permian Basin unproved leasehold properties	55,063		13,906		6,304

	San Juan Basin natural gas properties	236,045		—		—

	Total asset impairments from continuing operations	416,801		13,906		6,304

	Discontinued operations
	North Louisiana/East Texas oil and natural gas properties	1,936		29,794		—

	East Texas oil and natural gas properties	—		—		21,545

	Total asset impairments from discontinued operations	1,936		29,794		21,545

	Total asset impairments	$	418,737	$	43,700	$	27,849

Acquisition_and_Disposition_of1

Acquisition and Disposition of Properties (Tables)	12 Months Ended
	Dec. 31, 2014
Acquisition and Dispositions of Oil and Gas Properties [Abstract]
Schedule of Consideration Paid and Amounts of Assets Acquired and Liabilities Assumed	The following table summarizes the consideration paid and the amounts of the assets acquired and liabilities assumed recognized as of February 14, 2012 (including the effects of closing adjustments).



	(in thousands)
	Consideration given
	Cash (net)	$	67,615

	Recognized amounts of identifiable assets acquired and liabilities assumed
	Proved properties	$	65,581

	Unproved leasehold properties	911

	Accounts receivable	1,358

	Accounts payable	(25		)
	Asset retirement obligation	(210		)
	Total identifiable net assets	$	67,615

Discontinued_Operations_Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2014
Discontinued Operations and Disposal Groups [Abstract]
Schedule of Discontinued Operations	The table below provides a detail of these items included in income (loss) from discontinued operations as follows:



	Years ended December 31, (in thousands)	2014			2013			2012
	Alagasco net income	$	40,646		$	57,399		$	49,402

	Depreciation, depletion and amortization	(408		)	(598		)	(572		)
	General and administrative	3,337			5,894			5,166

	Interest expense	(17,306		)	(13,815		)	(1,693		)
	Other income	(347		)	(1,342		)	(977		)
	Income tax expense (benefit)	5,567			3,728			(727		)

	Alagasco income from discontinued operations	31,489			51,266			50,599

	Energen income (loss) from discontinued operations	(2,197		)	7,813			(1,658		)

	Income from discontinued operations	$	29,292		$	59,079		$	48,941

	As discussed in Note 14, Acquisition and Disposition of Properties, and above, the following tables detail held for sale properties by major classes of assets and liabilities:



	(in thousands)	31-Dec-14
					San Juan Basin*
	Oil and natural gas properties				$	1,166,124

	Less accumulated depreciation, depletion and amortization				(770,327		)
	Total assets held for sale				395,797

	Other long-term liabilities				(24,230		)
	Total liabilities held for sale				(24,230		)

	Total net assets held for sale				$	371,567

	*The San Juan Basin natural gas assets which are held for sale as of December 31, 2014, do not qualify for discontinued operations as we will have ongoing operations in the San Juan Basin.


	(in thousands)	31-Dec-13
		Alabama Gas Corporation			Black Warrior Basin			North Louisiana/East Texas			Total
	Cash	$	3,032		$	—		$	—		$	3,032

	Accounts receivable*	103,748			2,829			1,272			107,849

	Inventories	41,200			—			68			41,268

	Oil and natural gas properties	—			—			348,379			348,379

	Less accumulated depreciation, depletion and amortization	—						(301,609		)	(301,609		)

	Utility plant	1,491,433			—			—			1,491,433

	Less accumulated depreciation	(605,924		)	—			—			(605,924		)

	Other property, net	41			—			165			206

	Other current assets*	29,458			—			—			29,458

	Other long-term assets	128,780			—			—			128,780

	Total assets held for sale	1,191,768			2,829			48,275			1,242,872

	Accounts payable	(48,653		)	(1,732		)	(11		)	(50,396		)
Royalty payable	—			(550		)	(869		)	(1,419		)

Accrued taxes	(28,027		)	—			—			(28,027		)

Notes payable to banks	(50,000		)	—			—			(50,000		)

Other current liabilities*	(105,013		)	(379		)	(21		)	(105,413		)
Other long-term liabilities	(331,409		)	—			(14,983		)	(346,392		)

Long-term debt	(249,923		)	—			—			(249,923		)

Total liabilities held for sale	(813,025		)	(2,661		)	(15,884		)	(831,570		)
Total net assets held for sale	$	378,743		$	168		$	32,391		$	411,302

*At December 31, 2013, Alagasco’s accounts receivable included a consolidating adjustment of $4.7 million to adjust for affiliated companies receivables. Certain other current assets and other current liabilities at Alagasco of $1.6 million and $0.5 million, respectively, were reclassified to continuing operations at Energen.


Years ended December 31, (in thousands, except per share data)	2014			2013			2012
Natural gas distribution revenues	$	397,648		$	533,338		$	451,589

Oil and natural gas revenues	5,199			60,191			76,350

Total revenues	$	402,847		$	593,529		$	527,939

Pretax income from discontinued operations	$	47,220		$	92,253		$	79,197

Income tax expense	17,928			33,174			30,256

Income From Discontinued Operations	$	29,292		$	59,079		$	48,941

Gain on disposal of discontinued operations, net	$	724,594		$	5,605		$	—

Income tax expense	285,497			2,011			—

Gain on Disposal of Discontinued Operations, net	$	439,097		$	3,594		$	—

Total Income From Discontinued Operations	$	468,389		$	62,673		$	48,941

Diluted Earnings Per Average Common Share
Income from discontinued operations	$	0.4		$	0.81		$	0.68

Gain on disposal of discontinued operations, net	5.99			0.05			—

Total Income From Discontinued Operations	$	6.39		$	0.86		$	0.68

Basic Earnings Per Average Common Share
Income from discontinued operations	$	0.4		$	0.82		$	0.68

Gain on disposal of discontinued operations, net	6.02			0.05			—

Total Income From Discontinued Operations	$	6.42		$	0.87		$	0.68

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2014
Supplemental Cash Flow Information [Abstract]
Schedule of Cash Flow, Supplemental Disclosures	Supplemental information concerning Energen’s cash flow activities from continuing operations was as follows:



	Years ended December 31, (in thousands)	2014		2013		2012
	Interest paid, net of amount capitalized	$	32,172	$	38,255	$	46,224

	Income taxes paid	$	219,505	$	22,781	$	18,023

	Noncash investing activities:
	Accrued development, exploration costs and other capital	$	207,461	$	93,623	$	116,488

	Capitalized asset retirement obligations costs	$	2,958	$	2,772	$	3,994

	Capital lease obligations	$	—	$	—	$	5,072

	Receivable from sale of Alabama Gas Corporation	$	8,247	$	—	$	—

	Noncash financing activities:
	Issuance of common stock for employee benefit plans	$	2,448	$	1,015	$	838

	Treasury stock acquired in connection with tax withholdings	$	2,547	$	977	$	277

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Schedule of 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)	Cash Flow Hedges			Pension and Postretirement Plans			Total
	Balance as of December 31, 2013	$	12,178		$	(32,245	)	$	(20,067	)

	Other comprehensive loss before reclassifications	(261		)	(5,056		)	(5,317		)
	Amounts reclassified from accumulated other comprehensive income (loss)	(11,917		)	14,431			2,514

	Change in accumulated other comprehensive income (loss)	(12,178		)	9,375			(2,803		)

	Balance as of December 31, 2014	$	—		$	(22,870	)	$	(22,870	)

Reclassification out of Accumulated Other Comprehensive Income	The following table provides details of the reclassifications out of accumulated other comprehensive income (loss).



	Years ended December 31, (in thousands)	2014			2013
	(in thousands)	Amounts Reclassified						Line Item Where Presented
	Gains (losses) on cash flow hedges:
	Commodity contracts	$	21,611		$	35,684		Gain (loss) on derivative instruments, net

	Interest rate swap	(2,280		)	(1,723		)	Interest expense
	Total cash flow hedges	19,331			33,961

	Income tax expense	(7,414		)	(12,957		)
	Net of tax	11,917			21,004

	Pension and postretirement plans:
	Transition obligation	(22		)	(319		)	General and administrative
	Prior service cost	(248		)	(257		)	General and administrative
	Actuarial losses*	(21,932		)	(12,357		)	General and administrative
	Actuarial losses on settlement charges*	—			(421		)	Assets held for sale

	Total pension and postretirement plans	(22,202		)	(13,354		)
	Income tax benefit	7,771			4,674

	Net of tax	(14,431		)	(8,680		)
	Total reclassifications for the period	$	(2,514	)	$	12,324

	*In the first quarter of 2013, Energen incurred a settlement charge of $0.5 million for the payment of lump sums from the nonqualified supplemental retirement plans, of which $0.1 million was recognized in actuarial losses above and $0.4 million was recognized as a regulatory asset at Alagasco and reported in actuarial losses on settlement charges above. In the third quarter of 2013, Energen incurred a settlement charge of $64,000 for the payment of lump sums from the nonqualified supplemental retirement plans, of which $18,000 was recognized in actuarial losses above and $46,000 was recognized as a regulatory asset at Alagasco and reported in actuarial losses on settlement charges above.

Summarized_Quarterly_Financial1

Summarized Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Data [Abstract]
Schedule of Quarterly Operating Results	The following data summarizes quarterly operating results.



		Year ended December 31, 2014
	(in thousands, except per share amounts)	First			Second			Third			Fourth
	Revenues as originally reported	$	561,178		$	270,097		$	497,761		$	611,435

	Discontinued operations*	(263,900		)	—			—			—

	Adjusted revenues	$	297,278		$	270,097		$	497,761		$	611,435

	Operating income as originally reported	$	104,599		$	3,107		$	48,171		$	94,223

	Discontinued operations*	(73,139		)	—			—			—

	Adjusted operating income	$	31,460		$	3,107		$	48,171		$	94,223

	Income (loss) from continuing operations	$	15,647		$	(3,154	)	$	20,631		$	66,519

	Net income (loss)	$	53,316		$	(7,953	)	$	457,251		$	65,418

	Diluted earnings per average common share
	Continuing operations	$	0.21		$	(0.04	)	$	0.28		$	0.91

	Net income (loss)	$	0.73		$	(0.11	)	$	6.22		$	0.89

	Basic earnings per average common share
	Continuing operations	$	0.22		$	(0.04	)	$	0.28		$	0.91

	Net income (loss)	$	0.73		$	(0.11	)	$	6.26		$	0.9




		Year ended December 31, 2013
	(in thousands, except per share amounts)	First			Second			Third			Fourth
	Revenues as originally reported	$	492,679		$	490,057		$	320,406		$	472,733

	Discontinued operations*	(256,348		)	(123,076		)	(48,368		)	(142,771		)
	Adjusted revenues	$	236,331		$	366,981		$	272,038		$	329,962

	Operating income as originally reported	$	105,336		$	146,304		$	(4,052	)	$	110,630

	Discontinued operations*	(84,146		)	(7,667		)	21,487			(35,755		)

	Adjusted operating income	$	21,190		$	138,637		$	17,435		$	74,875

	Income from continuing operations	$	8,419		$	82,422		$	5,407		$	45,633

	Net income (loss)	$	56,692		$	83,067		$	(19,298	)	$	84,093

	Diluted earnings per average common share
	Continuing operations	$	0.12		$	1.14		$	0.07		$	0.62

	Net income (loss)	$	0.78		$	1.15		$	(0.27	)	$	1.15

	Basic earnings per average common share
	Continuing operations	$	0.12		$	1.14		$	0.07		$	0.63

	Net income (loss)	$	0.79		$	1.15		$	(0.27	)	$	1.16

	*As discussed in Note 15, Discontinued Operations and Held for Sale Properties, during the third quarter of 2014, Energen completed the transaction to sell Alagasco to Laclede. During the second quarter of 2014, Energen classified Alagasco as held for sale and reflected the associated operating results in discontinued operations. During the fourth quarter of 2013, Energen completed the sale of its Black Warrior Basin coalbed methane properties in Alabama. The property was classified as held for sale and reflected in discontinued operations during the third quarter of 2013. Also, during the third quarter of 2013, Energen classified its North Louisiana/East Texas natural gas and oil properties as held for sale and reflected the associated operating results in discontinued operations.

Oil_and_Natural_Gas_Operations1

Oil and Natural Gas Operations (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Oil and Gas Exploration and Production Industries Disclosures [Abstract]
Schedule of Capitalized Costs	The following table sets forth capitalized costs:



	(in thousands)	December 31, 2014			December 31, 2013
	Proved	$	8,069,638		$	7,043,779

	Unproved	142,340			168,975

	Total capitalized costs	8,211,978			7,212,754

	Accumulated depreciation, depletion and amortization	2,663,434			2,078,411

	Capitalized costs, net	$	5,548,544		$	5,134,343

Schedule of Cost Incurred in Property Acquisition, Exploration and Development Activities	The following table sets forth costs incurred in property acquisition, exploration and development activities and includes both capitalized costs and costs charged to expense during the year:



	Years ended December 31, (in thousands)	2014			2013			2012
	Property acquisition:
	Proved	$	2,582		$	4,661		$	79,862

	Unproved	68,514			26,820			58,634

	Exploration	972,164			435,636			419,284

	Development	408,949			655,353			749,256

	Total costs incurred	$	1,452,209		$	1,122,470		$	1,307,036

Schedule of Results of Operations from Producing Activities	The following table sets forth results of Energen’s oil, natural gas liquids and natural gas operations from producing activities:



	Years ended December 31, (in thousands)	2014			2013			2012
	Gross revenues*	$	1,679,213		$	1,206,293		$	1,090,948

	Production (lifting costs)	376,495			351,541			278,193

	Exploration expense	28,090			14,036			13,052

	Depreciation, depletion and amortization including asset impairments	960,539			463,606			345,873

	Accretion expense	7,608			6,995			6,339

	Income tax expense	99,469			128,773			160,551

	Results of operations from producing activities	$	207,012		$	241,342		$	286,940

	* The years ended December 31, 2014, 2013 and 2012 gross revenues include a pre-tax non-cash mark-to-market gain on derivatives of $315.4 million, a pre-tax non-cash mark-to-market loss on derivatives of $47.8 million and a pre-tax non-cash mark-to-market gain on derivatives of $58.8 million, respectively.
Schedule of Proved Developed and Undeveloped Oil and Gas Reserves	The independent reservoir engineers have issued reports covering approximately 99 percent of Energen’s ending proved reserves indicating that in their judgment the estimates are reasonable in the aggregate.



	Year ended December 31, 2014	Oil MBbl		NGL MBbl		Natural Gas MMcf		Total MMBOE
	Proved reserves at beginning of period	164,870		63,011		719,725		347.8

	Revisions of previous estimates	(48,548	)	(15,165	)	(71,806	)	(75.7	)
	Purchases	88		26		116		0.1

	Extensions and discoveries	76,722		29,695		141,209		130

	Production	(11,818	)	(4,104	)	(59,562	)	(25.8	)
	Sales	(87	)	—		(21,756	)	(3.7	)

	Proved reserves at end of period	181,227		73,463		707,926		372.7

	Proved developed reserves at end of period	118,697		47,621		589,074		264.5

	Proved undeveloped reserves at end of period	62,530		25,842		118,852		108.2




	Year ended December 31, 2013	Oil MBbl		NGL MBbl		Natural Gas MMcf		Total MMBOE
	Proved reserves at beginning of period	155,348		56,155		809,128		346.4

	Revisions of previous estimates	(680	)	2,211		18,465		4.6

	Purchases	142		56		282		0.2

	Extensions and discoveries	20,517		7,823		50,568		36.8

	Production	(10,378	)	(3,233	)	(70,506	)	(25.4	)
	Sales	(79	)	(1	)	(88,212	)	(14.8	)
	Proved reserves at end of period	164,870		63,011		719,725		347.8

	Proved developed reserves at end of period	113,795		42,087		623,305		259.8

	Proved undeveloped reserves at end of period	51,075		20,924		96,420		88




	Year ended December 31, 2012	Oil MBbl		NGL MBbl		Natural Gas MMcf		Total MMBOE
	Proved reserves at beginning of period	129,578		53,957		957,368		343.1

	Revisions of previous estimates	(8,546	)	(9,557	)	(143,704	)	(42.1	)
	Purchases	7,950		2,569		10,656		12.4

	Extensions and discoveries	35,132		11,759		61,170		57.1

	Production	(8,766	)	(2,573	)	(76,362	)	(24.1	)
	Proved reserves at end of period	155,348		56,155		809,128		346.4

	Proved developed reserves at end of period	105,976		36,440		708,657		260.5

	Proved undeveloped reserves at end of period	49,372		19,715		100,471		85.9

Schedule of Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves

	Years ended December 31, (in thousands)	2014			2013			2012
	Future gross revenues	$	20,971,672		$	19,509,305		$	17,735,363

	Future production costs	7,532,273			6,136,709			5,715,248

	Future development costs	1,784,738			1,896,602			1,892,600

	Future income tax expense	3,440,582			3,209,697			2,809,411

	Future net cash flows	8,214,079			8,266,297			7,318,104

	Discount at 10% per annum	3,994,423			4,248,456			3,618,785

	Standardized measure of discounted future net cash	$	4,219,656		$	4,017,841		$	3,699,319
	flows relating to proved oil and natural gas reserves
Schedule of Principal Sources of Changes in Standardized Measure of Discounted Future Net Cash Flows	The following are the principal sources of changes in the standardized measure of discounted future net cash flows:



	Years ended December 31, (in thousands)	2014			2013			2012
	Balance at beginning of year	$	4,017,841		$	3,699,319		$	3,629,163

	Revisions to reserves proved in prior years:
	Net changes in prices, production costs and future development costs	(1,147,028		)	566,838			(922,792		)

	Net changes due to revisions in quantity estimates	(1,285,394		)	(81,762		)	(383,755		)
	Development costs incurred, previously estimated	337,198			299,432			472,603

	Accretion of discount	401,784			369,932			362,916

	Changes in timing and other*	987,652			(179,502		)	(317,244		)

	Total revisions	(705,788		)	974,938			(788,272		)

	New field discoveries and extensions, net of future production and development costs	2,321,028			376,326			1,025,419

	Sales of oil and gas produced, net of production costs	(1,054,553		)	(1,014,593		)	(812,781		)
	Purchases	4,241			4,690			189,755

	Sales	(21,092		)	(24,876		)	—

	Net change in income taxes	(342,021		)	2,037			456,035

	Net change in standardized measure of discounted future net cash flows	201,815			318,522			70,156

	Balance at end of year	$	4,219,656		$	4,017,841		$	3,699,319

	*Amount represents changes in production timing and other. For 2014, the production timing is significantly affected by changes related to the acceleration of the horizontal drilling program and the delay of the vertical drilling program.

Organization_and_Basis_of_Pres1

Organization and Basis of Presentation (Sale of Alabama Gas Corporation) (Details) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 02, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on disposal of discontinued operations, net	$724,594,000	$5,605,000	$0
Alabama Gas Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal group, consideration				1,600,000,000
Debt assumed				267,000,000
Proceeds from sale				1,320,000,000
Gain on disposal of discontinued operations, net				$726,500,000

Summary_of_Significant_Account3

Summary of Significant Accounting Policies (Derivatives Gains and Losses) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net	$335,019	($50,024)	$84,153
Commodity Contract
Derivative Instruments, Gain (Loss) [Line Items]
Open non-cash mark-to-market gains (losses) on derivative instruments	315,445	-47,832	58,750
Closed gains (losses) on derivative instruments	19,574	-2,192	25,403
Gain (loss) on derivative instruments, net	$335,019	($50,024)	$84,153

Summary_of_Significant_Account4

Summary of Significant Accounting Policies (Discontinued Operations) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income From Discontinued Operations	$468,389	$62,673	$48,941
Income from discontinued operations	29,292	59,079	48,941
Alabama Gas Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Alagasco net income	40,646	57,399	49,402
Depreciation, depletion and amortization	-408	-598	-572
General and administrative	3,337	5,894	5,166
Interest expense	-17,306	-13,815	-1,693
Other income	-347	-1,342	-977
Income tax expense (benefit)	5,567	3,728	-727
Income From Discontinued Operations	31,489	51,266	50,599
Parent Company
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income From Discontinued Operations	($2,197)	$7,813	($1,658)

Summary_of_Significant_Account5

Summary of Significant Accounting Policies (Additional Information) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 30, 2013	Mar. 31, 2013
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	mbbl	mbbl
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Excess tax benefit from share-based compensation	$5.90	$3.10	$0.60
One year spot rate	0.70%
Derivatives transferred to not designated as hedging instruments				2,353	5,078
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Yield curve, term	0 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Yield curve, term	30 years

LongTerm_Debt_and_Notes_Payabl2

Long-Term Debt and Notes Payable (Schedule of Long-Term Debt) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt	1,039,000,000	$1,154,000,000
Long-term debt due within one year	0	60,000,000
Less unamortized debt discount	437,000	459,000
Long-term debt	1,038,563,000	1,093,541,000
Credit Facility \| Credit Facility
Debt Instrument [Line Items]
Long-term Debt, Gross	485,000,000	0
Medium-term Notes \| 7.40% Medium-term Notes, Series A, due July 24, 2017
Debt Instrument [Line Items]
Long-term Debt, Gross	2,000,000	2,000,000
Medium-term Notes \| 7.36% Medium-term Notes, Series A, due July 24, 2017
Debt Instrument [Line Items]
Long-term Debt, Gross	15,000,000	15,000,000
Medium-term Notes \| 7.23% Medium-term Notes, Series A, due July 28, 2017
Debt Instrument [Line Items]
Long-term Debt, Gross	2,000,000	2,000,000
Medium-term Notes \| 7.32% Medium-term Notes, Series A, due July 28, 2022
Debt Instrument [Line Items]
Long-term Debt, Gross	20,000,000	20,000,000
Medium-term Notes \| 7.60% Medium-term Notes, Series A, due July 26, 2027
Debt Instrument [Line Items]
Long-term Debt, Gross	5,000,000	5,000,000
Medium-term Notes \| 7.35% Medium-term Notes, Series A, due July 28, 2027
Debt Instrument [Line Items]
Long-term Debt, Gross	10,000,000	10,000,000
Medium-term Notes \| 7.125% Medium-term Notes, Series B, due February 15, 2028
Debt Instrument [Line Items]
Long-term Debt, Gross	100,000,000	100,000,000
Notes \| 7.40% Medium-term Notes, Series A, due July 24, 2017
Debt Instrument [Line Items]
Debt instrument, interest rate	7.40%
Notes \| 7.36% Medium-term Notes, Series A, due July 24, 2017
Debt Instrument [Line Items]
Debt instrument, interest rate	7.36%
Notes \| 7.23% Medium-term Notes, Series A, due July 28, 2017
Debt Instrument [Line Items]
Debt instrument, interest rate	7.23%
Notes \| 7.32% Medium-term Notes, Series A, due July 28, 2022
Debt Instrument [Line Items]
Debt instrument, interest rate	7.32%
Notes \| 7.60% Medium-term Notes, Series A, due July 26, 2027
Debt Instrument [Line Items]
Debt instrument, interest rate	7.60%
Notes \| 7.35% Medium-term Notes, Series A, due July 28, 2027
Debt Instrument [Line Items]
Debt instrument, interest rate	7.35%
Notes \| 7.125% Medium-term Notes, Series B, due February 15, 2028
Debt Instrument [Line Items]
Debt instrument, interest rate	7.13%
Notes \| 4.625% Notes, due September 1, 2021
Debt Instrument [Line Items]
Long-term Debt, Gross	400,000,000	400,000,000
Debt instrument, interest rate	4.63%
Senior Term Loans \| Senior Term Loans, (floating rate interest LIBOR plus 1.625%)
Debt Instrument [Line Items]
Long-term Debt, Gross	0	$600,000,000
Senior Term Loans \| Senior Term Loans, (floating rate interest LIBOR plus 1.625%) \| LIBOR
Debt Instrument [Line Items]
Debt Instrument, basis spread on variable rate	1.63%

LongTerm_Debt_and_Notes_Payabl3

Long-Term Debt and Notes Payable (Aggregate Maturities) (Details) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified	Dec. 31, 2014
Maturities of Long-term Debt [Abstract]
2015	$0
2016	0
2017	19,000
2018	0
2019	485,000
Thereafter	$535,000

LongTerm_Debt_and_Notes_Payabl4

Long-Term Debt and Notes Payable (Additional Information) (Details) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 02, 2014	Oct. 30, 2012	Nov. 17, 2014
Debt Instrument [Line Items]
Cross default provision, minimum threshold amount	$10,000,000
Credit facility, current borrowing capacity	2,000,000,000	1,250,000,000
Loan limit percentage (less than)	10.00%
Cross default provision, minimum debt default amount	75,000,000
Interest expense	37,771,000	39,736,000	47,565,000
Amortization of debt issuance costs	5,700,000	2,000,000	2,400,000
Interest expense, capitalized	200,000	200,000	500,000
Unused capacity, commitment fee percentage	30.00%
Senior Term Loans \| Senior Term Loans, (floating rate interest LIBOR plus 1.625%)
Debt Instrument [Line Items]
Long-term debt		600,000,000
Syndicated Credit Facility \| Credit Facility, September 2, 2014
Debt Instrument [Line Items]
Credit facilities				1,500,000,000		2,000,000,000
Debt instrument, term				5 years
Credit facility, current borrowing capacity				2,100,000,000
Debt covenant, debt to EBITDAX ratio	4
Debt covenant, current assets to current liabilities ratio	1
Debt covenant, minimum net present value of proved reserves to consolidated debt, ratio	1.5
Syndicated Credit Facility \| Credit Facility, October 30, 2012
Debt Instrument [Line Items]
Credit facilities					$1,250,000,000
Debt instrument, term					5 years

LongTerm_Debt_and_Notes_Payabl5

Long-Term Debt and Notes Payable (Lines of Credit) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Line of Credit Facility [Abstract]
Notes payable to banks	$485,000	$489,000
Available for borrowings	1,515,000	761,000
Credit facility, current borrowing capacity	2,000,000	1,250,000
Maximum amount outstanding at any month-end	750,000	859,000
Average daily amount outstanding	$482,166	$772,012
Average daily amount outstanding, weighted average interest rates	1.46%	1.39%
Amount outstanding at year-end, weighted average interest rates	1.67%	1.40%

Income_Taxes_Components_of_Inc

Income Taxes (Components of Income Taxes) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Taxes estimated to be payable currently:
Federal	$161,576	$23,342	$16,295
State	72,379	2,516	3,125
Total current	233,955	25,858	19,420
Taxes deferred:
Federal	144,645	85,950	119,053
State	-34,447	-2,300	5,346
Total deferred	110,198	83,650	124,399
Total income tax expense	$344,153	$109,508	$143,819

Income_Taxes_Components_of_Inc1

Income Taxes (Components of Income Taxes, Continuing and Discontinued Operations) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Income tax expense from continuing operations	$40,728	$74,323	$113,563
Income tax expense from discontinued operations	17,928	33,174	30,256
Income tax expense from gain on disposal of discontinued operations	285,497	2,011	0
Total income tax expense	$344,153	$109,508	$143,819

Income_Taxes_Deferred_Tax_Asse

Income Taxes (Deferred Tax Assets and Liabilities) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets:
Total deferred tax assets, Current	$25,533,000	$27,262,000
Total deferred tax assets, Noncurrent	70,320,000	23,579,000
Valuation allowance, Current	-1,122,000	-299,000
Valuation allowance, Noncurrent	-2,467,000	-2,674,000
Total deferred tax assets, net, Current	24,411,000	26,963,000
Total deferred tax assets, net, Noncurrent	67,853,000	20,905,000
Deferred tax liabilities:
Total deferred tax liabilities, Current	103,575,000	5,713,000
Total deferred tax liabilities, Noncurrent	1,068,339,000	828,519,000
Deferred tax liabilities, net, current	-79,164,000	0
Deferred tax liabilities, net, noncurrent	-1,000,486,000	-807,614,000
Deferred tax asset, net, current	0	21,250,000
Full valuation allowance	3,600,000
Oil and Gas Operations
Deferred tax liabilities:
State operating loss carryforwards and other tax carryforwards portion about to expire	254,600,000
Deferred tax assets, Current
Deferred tax assets:
Minimum tax credit	0	0
Allowance for doubtful accounts	244,000	251,000
Insurance and other accruals	2,537,000	3,082,000
Compensation accruals	11,355,000	12,925,000
Pension and other costs	0	0
Other comprehensive income	10,732,000	0
Derivative instruments	0	10,769,000
State net operating losses and other carryforwards	0	0
Other	665,000	235,000
Deferred tax assets, Noncurrent
Deferred tax assets:
Minimum tax credit	46,338,000	0
Allowance for doubtful accounts	0	0
Insurance and other accruals	0	0
Compensation accruals	0	0
Pension and other costs	7,009,000	3,652,000
Other comprehensive income	1,581,000	15,350,000
Derivative instruments	0	0
State net operating losses and other carryforwards	15,392,000	4,577,000
Other	0	0
Deferred tax liabilities:
State net operating loss carryforwards, subject to expiration	11,800,000
Deferred tax liabilities, Current
Deferred tax liabilities:
Depreciation and basis differences	0	0
Derivative instruments	102,691,000	0
Other comprehensive income	0	5,540,000
Other	884,000	173,000
Deferred tax liabilities, Noncurrent
Deferred tax liabilities:
Depreciation and basis differences	1,057,430,000	821,425,000
Derivative instruments	0	2,048,000
Other comprehensive income	0	0
Other	$10,909,000	$5,046,000

Income_Taxes_Effective_Income_

Income Taxes (Effective Income Tax Rate Reconciliation) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	35.00%
Income tax expense at statutory federal income tax rate	$49,130	$75,671	$111,364
State income taxes, net of federal income tax benefit	93	1,461	2,423
Impact of state law changes	-121	-1,966	0
Impact of state deferred tax revaluation on San Juan properties	-8,382	0	0
401(k) stock dividend deduction	-232	-449	-514
Other, net	240	-394	290
Total income tax expense	$40,728	$74,323	$113,563
Effective income tax rate (%)	29.01%	34.38%	35.69%

Income_Taxes_Unrecognized_Tax_

Income Taxes (Unrecognized Tax Benefits) (Details) (USD $)	12 Months Ended
Income Taxes (Unrecognized Tax Benefits) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits, Beginning Balance	$15,986,000	$12,555,000	$10,593,000
Additions based on tax positions related to the current year	3,873,000	4,546,000	3,731,000
Additions for tax positions of prior years	19,000	366,000	269,000
Reductions for tax positions of prior years	-954,000	-46,000	-446,000
Lapse of statute of limitations	-1,394,000	-1,435,000	-1,592,000
Unrecognized Tax Benefits, Ending Balance	17,530,000	15,986,000	12,555,000
Unrecognized tax benefits that would impact effective tax rate	7,600,000
Income tax interest expense (income) (net of tax benefit) and penalties expense (income)	27,000	15,000	25,000
Accrued interest (net of tax benefit) and penalties payments	$200,000	$200,000

Employee_Benefit_Plans_Benefit

Employee Benefit Plans (Benefit Obligations) (Details) (USD $)	3 Months Ended	12 Months Ended			3 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013
Benefit obligation:
Termination benefit charge	($2,500,000)
Amounts recognized in balance sheet
Noncurrent assets	0	0	8,894,000		8,894,000
Noncurrent liabilities	-15,935,000	-15,935,000	-47,484,000		-47,484,000
Amounts recognized to accumulated other comprehensive income:
Total accumulated other comprehensive income (loss)	22,870,000	22,870,000	32,245,000		32,245,000
Nonqualified Supplemental Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Reclassification of assets		11,000,000
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	107,669,000	107,669,000	225,969,000		225,969,000
Benefit obligation:
Balance at beginning of period		266,294,000	293,075,000
Service cost		8,329,000	13,293,000
Interest cost		5,325,000	10,161,000
Actuarial (gain) loss		9,078,000	-26,909,000
Curtailment gain		-8,496,000	-4,223,000
Transfer in connection with the sale of Alagasco		-124,783,000	0
Termination benefit charge		2,477,000	0	0
Retiree drug subsidy program		0	0
Benefits paid		-50,555,000	-19,103,000
Balance at end of period	107,669,000	107,669,000	266,294,000	293,075,000	266,294,000
Plan assets:
Fair value of plan assets at beginning of period		193,457,000	182,796,000
Actual return (loss) on plan assets		5,359,000	19,595,000
Employer contributions		19,164,000	10,169,000
Transfer in connection with the sale of Alagasco		-99,883,000	0
Benefits paid		-50,555,000	-19,103,000
Fair value of plan assets at end of period	67,542,000	67,542,000	193,457,000	182,796,000	193,457,000
Funded status of plan
Funded status of plans	-40,127,000	-40,127,000	-72,837,000		-72,837,000
Amounts recognized in balance sheet
Noncurrent assets	0	0	0		0
Noncurrent assets in assets held for sale	0	0	0		0
Current liabilities	-24,626,000	-24,626,000	-6,145,000		-6,145,000
Noncurrent liabilities	-15,501,000	-15,501,000	-47,485,000		-47,485,000
Noncurrent liabilities in liabilities related to assets held for sale	0	0	-19,207,000		-19,207,000
Net asset (liability) recognized	-40,127,000	-40,127,000	-72,837,000		-72,837,000
Amounts recognized to accumulated other comprehensive income:
Prior service costs, net of taxes	0	0	323,000		323,000
Net actuarial (gain) loss, net of taxes	22,246,000	22,246,000	37,479,000		37,479,000
Transition obligation, net of taxes	0	0	0		0
Total accumulated other comprehensive income (loss)	22,246,000	22,246,000	37,802,000		37,802,000
Postretirement Benefit Plans
Benefit obligation:
Balance at beginning of period		33,224,000	46,901,000
Service cost		262,000	1,125,000
Interest cost		716,000	1,931,000
Actuarial (gain) loss		6,385,000	-13,311,000
Curtailment gain		0	-1,255,000
Transfer in connection with the sale of Alagasco		-28,648,000	0
Termination benefit charge		0	0
Retiree drug subsidy program		48,000	124,000
Benefits paid		-860,000	-2,291,000
Balance at end of period	11,127,000	11,127,000	33,224,000		33,224,000
Plan assets:
Fair value of plan assets at beginning of period		55,459,000	48,194,000
Actual return (loss) on plan assets		-331,000	8,072,000
Employer contributions		21,000	1,484,000
Transfer in connection with the sale of Alagasco		-43,596,000	0
Benefits paid		-860,000	-2,291,000
Fair value of plan assets at end of period	10,693,000	10,693,000	55,459,000		55,459,000
Funded status of plan
Funded status of plans	-434,000	-434,000	22,235,000		22,235,000
Amounts recognized in balance sheet
Noncurrent assets	0	0	8,894,000		8,894,000
Noncurrent assets in assets held for sale	0	0	13,341,000		13,341,000
Current liabilities	0	0	0		0
Noncurrent liabilities	-434,000	-434,000	0		0
Noncurrent liabilities in liabilities related to assets held for sale	0	0	0		0
Net asset (liability) recognized	-434,000	-434,000	22,235,000		22,235,000
Amounts recognized to accumulated other comprehensive income:
Prior service costs, net of taxes	0	0	0		0
Net actuarial (gain) loss, net of taxes	624,000	624,000	-5,584,000		-5,584,000
Transition obligation, net of taxes	0	0	27,000		27,000
Total accumulated other comprehensive income (loss)	624,000	624,000	-5,557,000		-5,557,000
Black Warrior Basin
Benefit obligation:
Curtailment gain					($1,200,000)

Employee_Benefit_Plans_Other_I

Employee Benefit Plans (Other Investment Assets) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Level 3
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Unrealized gains relating to instruments held at the reporting date		$242
Transfer out of Level 3	-14,500	0
Nonqualified Supplemental Retirement Plans \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33,761		14,184
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at beginning of period			14,184
Fair value of plan assets at end of period	33,761		14,184
Nonqualified Supplemental Retirement Plans \| Insurance contracts \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14,805
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at end of period	14,805
Nonqualified Supplemental Retirement Plans \| United States equities \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,579
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at end of period	5,579
Nonqualified Supplemental Retirement Plans \| Global equities \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,338
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at end of period	2,338
Nonqualified Supplemental Retirement Plans \| Fixed income \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11,039		4,255
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at beginning of period			4,255
Fair value of plan assets at end of period	11,039		4,255
Nonqualified Supplemental Retirement Plans \| Cash and cash equivalents \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			9,929
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at beginning of period			9,929
Fair value of plan assets at end of period			9,929
Nonqualified Supplemental Retirement Plans \| Level 1 \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,917		9,929
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at beginning of period			9,929
Fair value of plan assets at end of period	7,917		9,929
Nonqualified Supplemental Retirement Plans \| Level 1 \| Insurance contracts \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at end of period	0
Nonqualified Supplemental Retirement Plans \| Level 1 \| United States equities \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,579
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at end of period	5,579
Nonqualified Supplemental Retirement Plans \| Level 1 \| Global equities \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,338
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at end of period	2,338
Nonqualified Supplemental Retirement Plans \| Level 1 \| Fixed income \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at beginning of period			0
Fair value of plan assets at end of period	0		0
Nonqualified Supplemental Retirement Plans \| Level 1 \| Cash and cash equivalents \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			9,929
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at beginning of period			9,929
Fair value of plan assets at end of period			9,929
Nonqualified Supplemental Retirement Plans \| Level 2 \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25,844		4,255
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at beginning of period			4,255
Fair value of plan assets at end of period	25,844		4,255
Nonqualified Supplemental Retirement Plans \| Level 2 \| Insurance contracts \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14,805
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at end of period	14,805
Nonqualified Supplemental Retirement Plans \| Level 2 \| United States equities \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at end of period	0
Nonqualified Supplemental Retirement Plans \| Level 2 \| Global equities \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at end of period	0
Nonqualified Supplemental Retirement Plans \| Level 2 \| Fixed income \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11,039		4,255
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at beginning of period			4,255
Fair value of plan assets at end of period	11,039		4,255
Nonqualified Supplemental Retirement Plans \| Level 2 \| Cash and cash equivalents \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at beginning of period			0
Fair value of plan assets at end of period			0
Nonqualified Supplemental Retirement Plans \| Level 3 \| Insurance contracts \| Deferred Costs, Noncurrent
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	5,600
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at beginning of period	5,600	5,332
Unrealized gains relating to instruments held at the reporting date	0	268
Transfer out of Level 3	-5,600	0
Fair value of plan assets at end of period	$0	$5,600

Employee_Benefit_Plans_Net_Per

Employee Benefit Plans (Net Periodic Benefit Cost) (Details) (USD $)	3 Months Ended		12 Months Ended
	Dec. 31, 2014	Sep. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Components of net periodic benefit cost:
Termination benefit charge	($2,500,000)
Nonqualified Supplemental Retirement Plans
Components of net periodic benefit cost:
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements		-18,000
Pension Plans
Components of net periodic benefit cost:
Service cost			8,329,000	13,293,000
Interest cost			5,325,000	10,161,000
Expected long-term return on assets			-4,386,000	-5,225,000	-5,134,000
Actuarial (gain) loss			9,078,000	-26,909,000
Prior service cost amortization			202,000	246,000	209,000
Actuarial loss amortization			4,995,000	6,919,000	3,945,000
Termination benefit charge			2,477,000	0	0
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements			4,082,000	161,000	0
Curtailment expense (gain)			254,000	-4,000	0
Net periodic expense			18,930,000	11,789,000	7,339,000
Postretirement Benefit Plans
Components of net periodic benefit cost:
Service cost			262,000	1,125,000
Interest cost			716,000	1,931,000
Expected long-term return on assets			-1,122,000	-787,000	-741,000
Actuarial (gain) loss			6,385,000	-13,311,000
Actuarial loss amortization			-653,000	-28,000	0
Termination benefit charge			0	0
Transition obligation amortization			44,000	229,000	248,000
Net periodic expense			-817,000	445,000	771,000
Continuing Operations \| Pension Plans
Components of net periodic benefit cost:
Service cost			6,808,000	5,196,000	4,023,000
Interest cost			4,498,000	4,496,000	4,296,000
Continuing Operations \| Postretirement Benefit Plans
Components of net periodic benefit cost:
Service cost			253,000	386,000	454,000
Interest cost			$661,000	$645,000	$810,000

Employee_Benefit_Plans_Other_C

Employee Benefit Plans (Other Comprehensive Income) (Details) (USD $)	3 Months Ended					12 Months Ended			3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2013	Mar. 31, 2013
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Settlement charges	$6,900,000
Settlement charges expensed	3,700,000
Black Warrior Basin
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Curtailments gain (loss)		1,200,000
Pension Plans
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Net actuarial (gain) loss experienced during the year						10,495,000	-14,138,000	28,748,000
Net actuarial loss recognized as expense						-25,433,000	-8,934,000	-4,908,000
Prior service cost recognized as expense						-246,000	-311,000	-340,000
Curtailment loss						-8,749,000	0	0
Total recognized in other comprehensive income (loss)						-23,933,000	-23,383,000	23,500,000
Curtailments gain (loss)						8,496,000	4,223,000
Settlement charges			39,000	300,000	400,000
Amortization of net actuarial loss						-841,000
Postretirement Benefit Plans
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Net actuarial (gain) loss experienced during the year						7,649,000	-8,057,000	-1,787,000
Net actuarial loss recognized as expense						1,908,000	550,000	0
Transition obligation recognized as expense						-48,000	-283,000	-294,000
Total recognized in other comprehensive income (loss)						9,509,000	-7,790,000	-2,081,000
Curtailments gain (loss)						0	1,255,000
Nonqualified Supplemental Retirement Plans
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Settlement charges	400,000		1,800,000	26,000					64,000	500,000
Settlement charges expensed										100,000
Nonqualified Supplemental Retirement Plans \| Alabama Gas Corporation
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Settlement charges									46,000	400,000
Long-term Disability Plan
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Expense related to long-term disability plan						200,000	200,000	200,000
Alagasco
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Curtailments gain (loss)			($300,000)

Employee_Benefit_Plans_Assumpt

Employee Benefit Plans (Assumptions) (Details)	12 Months Ended
Employee Benefit Plans (Assumptions) (Details)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Postretirement Benefit Plans
One year spot rate	0.70%
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Health care cost trend rate assumed for next year	7.25%	6.50%
Rate to which the cost trend rate is assumed to decline	5.00%	5.00%
Year that rate reaches ultimate rate	2021	2020
Pension Plans
Pension Plans
Discount rate	3.66%	3.63%	4.52%
Expected long-term return on plan assets	7.00%	7.00%	7.00%
Rate of compensation increase for pay-related plans	3.63%	3.71%	3.59%
Postretirement Benefit Plans
Discount rate	0.96%	4.29%
Rate of compensation increase	0.00%	3.63%
Postretirement Benefit Plans
Pension Plans
Discount rate	4.88%	4.36%	4.95%
Expected long-term return on plan assets	7.00%	7.00%	7.00%
Rate of compensation increase for pay-related plans	3.60%	3.70%	3.55%
Postretirement Benefit Plans
Discount rate	4.25%	4.95%
Rate of compensation increase	0.00%	3.60%

Employee_Benefit_Plans_Allocat

Employee Benefit Plans (Allocation of Plan Assets) (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Pension Plans
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation, Equity securities	100.00%
Actual plan asset allocations, Equity securities	100.00%	100.00%
Postretirement Benefit Plans
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation, Equity securities	100.00%
Actual plan asset allocations, Equity securities	100.00%	100.00%
Equity Securities \| Pension Plans
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation, Equity securities	0.00%
Actual plan asset allocations, Equity securities	0.00%	34.00%
Equity Securities \| Postretirement Benefit Plans
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation, Equity securities	60.00%
Actual plan asset allocations, Equity securities	60.00%	61.00%
Debt Securities \| Pension Plans
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation, Equity securities	0.00%
Actual plan asset allocations, Equity securities	0.00%	28.00%
Debt Securities \| Postretirement Benefit Plans
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation, Equity securities	40.00%
Actual plan asset allocations, Equity securities	40.00%	39.00%
Other Securities \| Pension Plans
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation, Equity securities	100.00%
Actual plan asset allocations, Equity securities	100.00%	38.00%
Other Securities \| Postretirement Benefit Plans
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation, Equity securities	0.00%
Actual plan asset allocations, Equity securities	0.00%	0.00%

Employee_Benefit_Plans_Fair_Va

Employee Benefit Plans (Fair Value of Plan Assets) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$14,500
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period	14,500	17,399
Unrealized gains (losses)		992
Unrealized gains relating to instruments held at the reporting date		242
Settlements		-4,948
Purchases		815
Transfer out of Level 3	-14,500	0
Fair value of plan assets at end of period		14,500
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	193,457	182,796	67,542
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			67,542
Fair value of plan assets at end of period	193,457	182,796	67,542
Pension Plans \| Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	60,231		67,542
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			67,542
Fair value of plan assets at end of period	60,231		67,542
Pension Plans \| Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	133,226		0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			0
Fair value of plan assets at end of period	133,226		0
Pension Plans \| Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period	14,500
Unrealized gains (losses)	0
Unrealized gains relating to instruments held at the reporting date	0
Settlements	0
Purchases	0
Fair value of plan assets at end of period	0
Pension Plans \| United States equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	34,117
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of period	34,117
Pension Plans \| United States equities \| Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	34,117
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of period	34,117
Pension Plans \| United States equities \| Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of period	0
Pension Plans \| Global equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	28,780
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of period	28,780
Pension Plans \| Global equities \| Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20,144
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of period	20,144
Pension Plans \| Global equities \| Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8,636
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of period	8,636
Pension Plans \| Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	50,777
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of period	50,777
Pension Plans \| Fixed income \| Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of period	0
Pension Plans \| Fixed income \| Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	50,777
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of period	50,777
Pension Plans \| Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	37,292
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of period	37,292
Pension Plans \| Alternative investments \| Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of period	0
Pension Plans \| Alternative investments \| Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	37,292
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of period	37,292
Pension Plans \| Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	42,491		67,542
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			67,542
Fair value of plan assets at end of period	42,491		67,542
Pension Plans \| Cash and cash equivalents \| Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,970		67,542
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			67,542
Fair value of plan assets at end of period	5,970		67,542
Pension Plans \| Cash and cash equivalents \| Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	36,521		0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			0
Fair value of plan assets at end of period	36,521		0
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55,459	48,194	10,693
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			10,693
Fair value of plan assets at end of period	55,459	48,194	10,693
Postretirement Benefit Plans \| Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33,715		6,426
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			6,426
Fair value of plan assets at end of period	33,715		6,426
Postretirement Benefit Plans \| Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21,744		4,267
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			4,267
Fair value of plan assets at end of period	21,744		4,267
Postretirement Benefit Plans \| United States equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24,152		4,715
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			4,715
Fair value of plan assets at end of period	24,152		4,715
Postretirement Benefit Plans \| United States equities \| Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24,152		4,715
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			4,715
Fair value of plan assets at end of period	24,152		4,715
Postretirement Benefit Plans \| United States equities \| Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			0
Fair value of plan assets at end of period	0		0
Postretirement Benefit Plans \| Global equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9,563		1,711
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			1,711
Fair value of plan assets at end of period	9,563		1,711
Postretirement Benefit Plans \| Global equities \| Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9,563		1,711
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			1,711
Fair value of plan assets at end of period	9,563		1,711
Postretirement Benefit Plans \| Global equities \| Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			0
Fair value of plan assets at end of period	0		0
Postretirement Benefit Plans \| Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21,744		4,267
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			4,267
Fair value of plan assets at end of period	21,744		4,267
Postretirement Benefit Plans \| Fixed income \| Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			0
Fair value of plan assets at end of period	0		0
Postretirement Benefit Plans \| Fixed income \| Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21,744		4,267
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			4,267
Fair value of plan assets at end of period	$21,744		$4,267

Employee_Benefit_Plans_Cash_Fl

Employee Benefit Plans (Cash Flows) (Details) (USD $)	12 Months Ended
Employee Benefit Plans (Cash Flows) (Details) (USD $)	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Anticipated required or discretionary contributions during in next fiscal year	$13,700,000
Pension Plans
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2015	92,711,000
2016	14,601,000
2017	113,000
2018	110,000
2019	107,000
2020-2024	484,000
Postretirement Benefit Plans
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2015	324,000
2016	397,000
2017	472,000
2018	541,000
2019	583,000
2020-2024	3,266,000
Nonqualified Supplemental Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Anticipated required or discretionary contributions during in next fiscal year	$11,000,000

Common_Stock_Plans_Energen_Emp

Common Stock Plans (Energen Employee Savings Plan) (Details) (Energen Employee Savings Plan, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Energen Employee Savings Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of common stock that might be diversified into other investment options	100.00%
Expense associated with contributions to employee savings plan	$3.70	$3.70	$3.30

Common_Stock_Plans_Stock_Incen

Common Stock Plans (Stock Incentive Plan) (Details) (Stock Incentive Plan)	Dec. 31, 2014	Apr. 27, 2011
Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for issuance		8,600,000
Number of shares remaining for issuance	2,635,544

Common_Stock_Plans_Performance

Common Stock Plans (Performance Share Awards) (Details) (Performance share awards, Stock Incentive Plan, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Each unit of performance share awards equivalent to market value of number of common stock (shares)	1
Shares
Nonvested, Beginning of Period, Shares	160,819	0
Forfeited, Shares		-8,008
Nonvested, End of Period, Shares	212,968	160,819
Weighted Average Price
Nonvested, Beginning of Period, Weighted Average Price (in dollars per share)	$62.13	$0
Forfeited, Weighted Average Price (in dollars per share)		$60.03
Nonvested, End of Period, Weighted Average Price (in dollars per share)	$71.53	$62.13
Vested and paid, Shares	-14,097
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested and Paid, Weighted Average Grant Date Fair Value	$70.06
Two years vesting period
Shares
Granted, Shares	937	86,221
Weighted Average Price
Granted, Weighted Average Price (in dollars per share)	$131.56	$61.14
Three years vesting period
Shares
Granted, Shares	65,309	82,606
Weighted Average Price
Granted, Weighted Average Price (in dollars per share)	$93.49	$62.96

Common_Stock_Plans_Stock_Optio

Common Stock Plans (Stock Options) (Details) (Stock Incentive Plan, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Shares
Remaining reserved for issuance	2,635,544
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, vesting period	3 years
Share-based compensation, expiration period	10 years
Shares
Outstanding, Beginning of Period, Shares	1,191,044	1,648,475	1,338,241
Granted, Shares	110,307	137,762	371,040
Exercised, Shares	-544,280	-590,119	-58,471
Forfeited, Shares		-5,074	-2,335
Outstanding, End of Period, Shares	757,071	1,191,044	1,648,475
Exercisable, Shares	454,938	713,445	987,733
Remaining reserved for issuance	2,635,544
Weighted Average Exercise Price
Outstanding, Beginning of Period, Weighted Average Exercise Price (in dollars per share)	$51.06	$47.58	$44.77
Granted, Weighted Average Exercise Price (in dollars per share)	$72.55	$49.22	$54.11
Exercised, Weighted Average Exercise Price (in dollars per share)	$50.09	$40.92	$24.55
Forfeited, Weighted Average Exercise Price (in dollars per share)		$51.85	$46.45
Outstanding, End of Period, Weighted Average Exercise Price (in dollars per share)	$54.88	$51.06	$47.58
Exercisable, Weighted Average Exercise Price (in dollars per share)	$51.88	$49.80	$43.75

Common_Stock_Plans_Stock_Optio1

Common Stock Plans (Stock Options, Valuation Assumptions) (Details) (Stock options, Stock Incentive Plan, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	110,307	137,762	371,040
April 15, 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	2,439
Fair market value of stock option at grant (in dollars per share)	32.22
Expected life of award	5 years 9 months 18 days
Risk-free interest rate	1.93%
Annualized volatility rate	40.70%
Dividend yield	0.20%
January 22, 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	107,868
Fair market value of stock option at grant (in dollars per share)	27.57
Expected life of award	5 years 9 months 18 days
Risk-free interest rate	2.06%
Annualized volatility rate	40.70%
Dividend yield	0.80%
October 15, 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	3,686
Fair market value of stock option at grant (in dollars per share)	30.53
Expected life of award	5 years 9 months 18 days
Risk-free interest rate	1.79%
Annualized volatility rate	40.60%
Dividend yield	0.70%
January 24, 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	134,076
Fair market value of stock option at grant (in dollars per share)	16.66
Expected life of award	5 years 9 months 18 days
Risk-free interest rate	1.01%
Annualized volatility rate	40.30%
Dividend yield	1.20%
January 25, 2012 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	371,040
Fair market value of stock option at grant (in dollars per share)	18.79
Expected life of award	5 years 9 months 18 days
Risk-free interest rate	1.07%
Annualized volatility rate	39.60%
Dividend yield	1.00%

Common_Stock_Plans_Stock_Optio2

Common Stock Plans (Stock Options, Textual) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Performance share awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$6,200,000	$3,800,000	$0
Tax benefit related to stock-based compensation	2,300,000	1,400,000
Costs not recognized	5,600,000
Period for recognition	1 year 5 months 12 days
Stock options \| Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	2,900,000	3,400,000	6,200,000
Tax benefit related to stock-based compensation	1,100,000	1,300,000	2,300,000
Intrinsic value of stock options exercised during period	18,500,000
Cash received from exercise of stock options	23,100,000
Intrinsic value for outstanding options	7,800,000
Intrinsic value for exercisable options	5,400,000
Fair value of vested options	5,000,000
Unrecognized compensation cost	500,000
Stock Appreciation Rights \| Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	400,000	9,900,000	900,000
Intrinsic value of stock options exercised during period	4,400,000
Cash paid for settlement of stock appreciation rights	$3,000,000
Stock Appreciation Rights \| 2004 Stock Appreciation Rights Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining requisite service period (in years)	3 years

Common_Stock_Plans_Stock_Optio3

Common Stock Plans (Stock Options, Range of Exercise Prices) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of exercisable options, Weighted Average Remaining Contractual Life (in years)	5 years 9 months 15 days
Stock options \| Stock Incentive Plan
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices, Lower Range Limit	29.79
Number of outstanding options, Range of Exercise Prices, Upper Range Limit	80.48
Number of outstanding options, Shares	757,071
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	6 years 8 months 5 days
Stock options \| Stock Incentive Plan \| $46.45
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	46.45
Number of outstanding options, Shares	25,470
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	2 years
Stock options \| Stock Incentive Plan \| $60.56
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	60.56
Number of outstanding options, Shares	48,560
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	3 years
Stock options \| Stock Incentive Plan \| $29.79
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	29.79
Number of outstanding options, Shares	35,161
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	4 years
Stock options \| Stock Incentive Plan \| $46.69
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	46.69
Number of outstanding options, Shares	26,481
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	5 years
Stock options \| Stock Incentive Plan \| $54.99
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	54.99
Number of outstanding options, Shares	111,487
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	6 years
Stock options \| Stock Incentive Plan \| $54.11
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	54.11
Number of outstanding options, Shares	271,848
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	7 years
Stock options \| Stock Incentive Plan \| $48.36
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	48.36
Number of outstanding options, Shares	124,071
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	8 years
Stock options \| Stock Incentive Plan \| $80.48
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	80.48
Number of outstanding options, Shares	3,686
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	8 years 9 months 15 days
Stock options \| Stock Incentive Plan \| $72.39
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	72.39
Number of outstanding options, Shares	107,868
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	9 years
Stock options \| Stock Incentive Plan \| $79.63
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	79.63
Number of outstanding options, Shares	2,439
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	9 years

Common_Stock_Plans_Restricted_

Common Stock Plans (Restricted Stock) (Details) (Non-vested restricted stock, Stock Incentive Plan, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Non-vested restricted stock \| Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, vesting period	3 years
Share-based compensation expense	$3,200,000	$1,900,000	$100,000
Tax benefit related to stock-based compensation	1,200,000	700,000	23,000
Unrecognized compensation cost	$1,300,000
Remaining requisite service period (in years)	1 year 5 months 16 days
Shares
Nonvested, Beginning of Period, Shares	62,518	11,115	9,275
Granted, Shares	48,904	52,650	11,115
Forfeited, Shares		-1,247
Vested, Shares	-11,848		-9,275
Nonvested, End of Period, Shares	99,574	62,518	11,115
Weighted Average Price
Nonvested, Beginning of Period, Weighted Average Price (in dollars per share)	$51.16	$45.24	$42.99
Granted, Weighted Average Price (in dollars per share)	$71.91	$52.34	$45.24
Forfeited, Weighted Average Price (in dollars per share)		$48.36
Vested and paid, Weighted Average Price (in dollars per share)	$65.94		$42.97
Nonvested, End of Period, Weighted Average Price (in dollars per share)	$59.60	$51.16	$45.24

Common_Stock_Plans_2004_Stock_

Common Stock Plans (2004 Stock Appreciation Rights Plan) (Details) (Stock Appreciation Rights, 2004 Stock Appreciation Rights Plan, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Shares
Outstanding, Beginning of Period, Shares	377,377	653,030	777,218
Granted, Shares	62,749	88,000
Exercised/forfeited, Shares	-164,976	-363,653	-124,188
Outstanding, End of Period, Shares	275,150	377,377	653,030
Weighted Average Exercise Price
Outstanding, Beginning of Period, Weighted Average Exercise Price (in dollars per share)	$49.48	$44.14	$42
Granted, Weighted Average Exercise Price (in dollars per share)	$72.39	$48.36
Exercised/forfeited, Weighted Average Exercise Price (in dollars per share)	$52.37	$39.66	$30.90
Outstanding, End of Period, Weighted Average Exercise Price (in dollars per share)	$52.96	$49.48	$44.14
January 27, 2010 [Member] \| Originally reported
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	171,749
Fair market value of stock option at grant (in dollars per share)	$22.50
Expected life of award	2 years 6 months 15 days
Risk-free interest rate	0.90%
Annualized volatility rate	33.40%
Dividend yield	0.13%
February 13-16, 2009 [Member] \| Originally reported
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	3,292
Fair market value of stock option at grant (in dollars per share)	$33.23
Expected life of award	2 years 0 months 15 days
Risk-free interest rate	0.67%
Annualized volatility rate	33.40%
Dividend yield	0.13%
January 22, 2014 [Member] \| Originally reported
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	62,749
Fair market value of stock option at grant (in dollars per share)	$18.63
Expected life of award	5 years 6 months 22 days
Risk-free interest rate	1.77%
Annualized volatility rate	33.40%
Dividend yield	0.13%
January 24, 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	931
Fair market value of stock option at grant (in dollars per share)	$20.14
Expected life of award	2 years
Risk-free interest rate	0.65%
Annualized volatility rate	33.40%
Dividend yield	0.13%
January 24, 2013 [Member] \| Originally reported
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	87,069
Fair market value of stock option at grant (in dollars per share)	$25.93
Expected life of award	4 years 6 months 26 days
Risk-free interest rate	1.57%
Annualized volatility rate	33.40%
Dividend yield	0.13%
January 26, 2011 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	7,785
Fair market value of stock option at grant (in dollars per share)	$16.27
Expected life of award	2 years
Risk-free interest rate	0.65%
Annualized volatility rate	33.40%
Dividend yield	0.13%
January 26, 2011 [Member] \| Originally reported
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	182,199
Fair market value of stock option at grant (in dollars per share)	$19.15
Expected life of award	3 years 0 months 15 days
Risk-free interest rate	1.12%
Annualized volatility rate	33.40%
Dividend yield	0.13%
January 28, 2009 [Member] \| Originally reported
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	305,257
Fair market value of stock option at grant (in dollars per share)	$34.66
Expected life of award	2 years 0 months 15 days
Risk-free interest rate	0.67%
Annualized volatility rate	33.40%
Dividend yield	0.13%
February 4, 2008 [Member] \| Originally reported
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	67,093
Fair market value of stock option at grant (in dollars per share)	$10.57
Expected life of award	1 year 6 months 18 days
Risk-free interest rate	0.45%
Annualized volatility rate	33.40%
Dividend yield	0.13%
February 1, 2007 [Member] \| Originally reported
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Awards granted	85,906
Fair market value of stock option at grant (in dollars per share)	$19.25
Expected life of award	1 year 0 months 15 days
Risk-free interest rate	0.26%
Annualized volatility rate	33.40%
Dividend yield	0.13%

Common_Stock_Plans_Other_Plans

Common Stock Plans (Other Plans) (Details) (USD $)	12 Months Ended
Common Stock Plans (Other Plans) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Stock Equivalent Units \| Petrotech Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, Beginning of Period, Shares	173,292	141,243	11,061	213,870
Granted	76,084
Paid, Shares	-4,431	-36,792	-3,281
Forfeited	-31,075	-26,529	-13,476
Share-based compensation expense	$4,500,000	$6,200,000	$2,600,000
Stock Equivalent Units \| Petrotech Incentive Plan \| Three years vesting period
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted		92,418	102,349
Share-based compensation, vesting period		3 years	3 years
Stock Equivalent Units \| Petrotech Incentive Plan \| Two years vesting period
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted			3,768
Share-based compensation, vesting period			2 years
Stock Equivalent Units \| Petrotech Incentive Plan \| 18-months vesting period
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted			40,822
Share-based compensation, vesting period			18 months
Stock Equivalent Units \| Petrotech Incentive Plan \| 17-month vesting period
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted		2,952
Share-based compensation, vesting period		17 months
Management \| 1997 Deferred Compensation Plan
Deferred Compensation Arrangements [Abstract]
Deferred compensation, reserved for issuance	691,222			691,222
Director \| Stock options \| 1992 Energen Corporation Directors Stock Plan
Deferred Compensation Arrangements [Abstract]
Granted, Shares	10,360	13,500	11,120
Number of shares remaining for issuance	127,924

Common_Stock_Plans_Stock_Repur

Common Stock Plans (Stock Repurchase Program) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 22, 2014
Equity, Class of Treasury Stock [Line Items]
Purchase and retirement of shares, value	$14,913,000
Common Stock
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount				3,600,000
Stock repurchase program, remaining authorized repurchase amount	3,373,161
Shares acquired in connection with stock compensation plans	32,768	14,766	5,459
Common Stock
Equity, Class of Treasury Stock [Line Items]
Purchase and retirement of shares, shares	226,839	0	0
Purchase and retirement of shares, value	$2,000

Derivative_Commodity_Instrumen2

Derivative Commodity Instruments (Offsetting of Derivative Assets and Liabilities) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets
Gross Amounts Recognized at Fair Value	$339,977	$44,215
Gross Amounts Offset in the Balance Sheets	-17,640	-21,313
Net Amount Presented in the Balance Sheets	322,337	22,902
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	322,337	22,902
Liabilities
Gross Amounts Recognized at Fair Value	18,628	51,615
Gross Amounts Offset in the Balance Sheets	-17,640	-21,313
Net Amount Presented in the Balance Sheets	988	30,302
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	988	30,302
Total derivatives	321,349	-7,400
Current Assets
Assets
Gross Amounts Recognized at Fair Value	339,977	36,223
Gross Amounts Offset in the Balance Sheets	-17,640	-18,760
Net Amount Presented in the Balance Sheets	322,337	17,463
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	322,337	17,463
Noncurrent Assets
Assets
Gross Amounts Recognized at Fair Value	0	7,992
Gross Amounts Offset in the Balance Sheets	0	-2,553
Net Amount Presented in the Balance Sheets	0	5,439
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	0	5,439
Current Liabilities
Liabilities
Gross Amounts Recognized at Fair Value	18,628	49,062
Gross Amounts Offset in the Balance Sheets	-17,640	-18,760
Net Amount Presented in the Balance Sheets	988	30,302
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	988	30,302
Noncurrent Liabilities
Liabilities
Gross Amounts Recognized at Fair Value	0	2,553
Gross Amounts Offset in the Balance Sheets	0	-2,553
Net Amount Presented in the Balance Sheets	0	0
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	$0	$0

Derivative_Commodity_Instrumen3

Derivative Commodity Instruments (Cash Flow Hedging Relationship in Financial Statements) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net gain (loss) recognized in other comprehensive income on derivatives (effective portion), net of tax of $23, ($6,660) and $40,720	$37	($10,866)	$66,438
Gain (Loss) Recognized in other comprehensive income on derivatives	23	-6,660	40,720
Gain (Loss) on Derivative Instruments, Net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain reclassified from accumulated other comprehensive income into income (effective portion)	21,612	34,293	52,694
Gain (loss) recognized in income on derivatives (ineffective portion and amount excluded from effectiveness testing)	$0	$835	($5,340)

Derivative_Commodity_Instrumen4

Derivative Commodity Instruments (Effect of Open and Closed Derivative Commodity Instruments Not Designated as Hedging Instruments) (Details) (Gain (Loss) on Derivative Instruments, Net, USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Gain (Loss) on Derivative Instruments, Net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Open non-cash mark-to-market gains (losses) on derivative instruments	$313,408	($73,980)	$61,841

Derivative_Commodity_Instrumen5

Derivative Commodity Instruments (Reclassification) (Details) (Production Period, Year One)	12 Months Ended
	Dec. 31, 2014
	mbbl
NYMEX Swaps \| Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes	8,280
Average contract price	89.3
WTS/WTI Basis Swaps \| Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes	2,160	[1]
Average contract price	-4.3	[1]
WTI/WTI Basis Swaps \| Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes	6,840	[2]
Average contract price	-4.82	[2]
Basin Specific Swaps, San Juan \| Natural Gas
Derivatives, Fair Value [Line Items]
Total Hedged Volumes	23
Average Contract Price, Per Mcf	4.13
Basin Specific Swaps - Permain \| Natural Gas
Derivatives, Fair Value [Line Items]
Total Hedged Volumes	8
Average Contract Price, Per Mcf	4.25

[1]	WTS - West Texas Sour/Midland, WTI - West Texas Intermediate/Cushing
[2]	WTI - West Texas Intermediate/Midland, WTI - West Texas Intermediate/Cushing

Derivative_Commodity_Instrumen6

Derivative Commodity Instruments (Additional Information) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	counterparty	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	counterparty	Dec. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Deferred tax assets (liabilities), net					$8,200,000					$8,200,000
Counterparties with whom company holds net gain positions	13								13
Counterparties with whom company holds net loss positions	1								1
Gain (Loss) on fair value of derivatives									335,019,000	-50,024,000	84,153,000
Total revenues	611,435,000	497,761,000	270,097,000	297,278,000	329,962,000	272,038,000	366,981,000	236,331,000	1,679,213,000	1,206,293,000	1,090,948,000
Commodity Contract
Derivative [Line Items]
Gain (Loss) on fair value of derivatives									335,019,000	-50,024,000	84,153,000
J.P Morgan Ventures \| Commodity Contract
Derivative [Line Items]
Gain (Loss) on fair value of derivatives									58,500,000
Merrill Lynch Commodities \| Commodity Contract
Derivative [Line Items]
Gain (Loss) on fair value of derivatives									46,300,000
Barclays Bank \| Commodity Contract
Derivative [Line Items]
Gain (Loss) on fair value of derivatives									39,000,000
Morgan Stanley Capital Group \| Commodity Contract
Derivative [Line Items]
Gain (Loss) on fair value of derivatives									35,200,000
Canadian Imperial Bank of Commerce \| Commodity Contract
Derivative [Line Items]
Gain (Loss) on fair value of derivatives									34,900,000
Bank of Montreal \| Commodity Contract
Derivative [Line Items]
Gain (Loss) on fair value of derivatives									34,300,000
Accumulated Net Gain from Discontinued Hedge Accounting \| Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Total revenues									$1,500,000

Fair_Value_Measurements_Deriva

Fair Value Measurements (Derivative Instruments, Fair Value) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Noncurrent derivative instruments	$0	$5,439
Net Amount Presented in the Balance Sheets	322,337	22,902
Total liabilities	-988	-30,302
Fair Value, Measurements, Recurring
Derivative [Line Items]
Derivative instruments	322,337	17,463
Noncurrent derivative instruments		5,439
Net Amount Presented in the Balance Sheets	322,337	22,902
Derivative instruments	-988	-30,302
Total liabilities	-988	-30,302
Net derivative asset (liability)	321,349	-7,400
Level 2 \| Fair Value, Measurements, Recurring
Derivative [Line Items]
Derivative instruments	294,865	-1,658
Noncurrent derivative instruments		4,383
Net Amount Presented in the Balance Sheets	294,865	2,725
Derivative instruments	2,048	-28,414
Total liabilities	2,048	-28,414
Net derivative asset (liability)	296,913	-25,689
Level 3 \| Fair Value, Measurements, Recurring
Derivative [Line Items]
Derivative instruments	27,472	19,121
Noncurrent derivative instruments		1,056
Net Amount Presented in the Balance Sheets	27,472	20,177
Derivative instruments	-3,036	-1,888
Total liabilities	-3,036	-1,888
Net derivative asset (liability)	$24,436	$18,289

Fair_Value_Measurements_Deriva1

Fair Value Measurements (Derivative Instruments Change in Fair Value of Level 3) (Details) (Derivative Commodity Instruments, USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Derivative Commodity Instruments
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$18,289,000	[1]	$89,019,000	[1]	$65,801,000
Realized gains	22,208,000		55,210,000		63,720,000
Unrealized gains (losses) relating to instruments held at the reporting date	2,981,000	[2]	-71,367,000	[2]	22,160,000	[2]
Settlements during period	-19,042,000		-54,573,000		-62,662,000
Balance at end of period	24,436,000	[1]	18,289,000	[1]	89,019,000	[1]
Unrealized gain (loss) on derivatives and commodity contracts	20,200,000		-7,600,000		19,900,000
Gain on sale of natural gas liquids and Gas Daily contracts	$3,200,000

[1]	Included in the Level 3 fair value at December 31, 2014 are gains of $3.2 million from natural gas liquids and Gas Daily contracts which were closed at December 31, 2014 but not cash settled.
[2]	Includes $20.2 million in mark-to-market gains, $7.6 million in mark-to-market losses and $19.9 million in mark-to-market gains for the years ended December 31, 2014, 2013 and 2012, respectively.

Fair_Value_Measurements_Level_

Fair Value Measurements (Level 3 Fair Value Measurements of Derivative Commodity Instruments) (Details) (2015, Level 3, USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Natural Gas \| San Juan Basin
Fair Value, Option, Quantitative Disclosures [Line Items]
Net derivative asset (liability), at fair value (in USD)	$28,597
Natural Gas \| Permian Basin
Fair Value, Option, Quantitative Disclosures [Line Items]
Net derivative asset (liability), at fair value (in USD)	10,927
Crude Oil \| WTS/WTI Basis Swaps
Fair Value, Option, Quantitative Disclosures [Line Items]
Net derivative asset (liability), at fair value (in USD)	-3,836
Crude Oil \| WTI/WTI Basis Swaps
Fair Value, Option, Quantitative Disclosures [Line Items]
Net derivative asset (liability), at fair value (in USD)	($14,419)
Discounted Cash Flow Valuation Technique \| Natural Gas \| Permian Basin
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value inputs, derivative, nonmonetary notional amount (USD per Mcf)	0.15	[1]
Discounted Cash Flow Valuation Technique \| Minimum [Member] \| Natural Gas \| WTS/WTI Basis Swaps
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value inputs, derivative, nonmonetary notional amount (USD per Mcf)	2.55	[1]
Discounted Cash Flow Valuation Technique \| Minimum [Member] \| Natural Gas \| WTI/WTI Basis Swaps
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value inputs, derivative, nonmonetary notional amount (USD per Mcf)	2.72	[1]
Discounted Cash Flow Valuation Technique \| Minimum [Member] \| Natural Gas \| San Juan Basin
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value inputs, derivative, nonmonetary notional amount (USD per Mcf)	0.13	[1]
Discounted Cash Flow Valuation Technique \| Maximum [Member] \| Natural Gas \| WTS/WTI Basis Swaps
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value inputs, derivative, nonmonetary notional amount (USD per Mcf)	2.66	[1]
Discounted Cash Flow Valuation Technique \| Maximum [Member] \| Natural Gas \| WTI/WTI Basis Swaps
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value inputs, derivative, nonmonetary notional amount (USD per Mcf)	2.82	[1]
Discounted Cash Flow Valuation Technique \| Maximum [Member] \| Natural Gas \| San Juan Basin
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value inputs, derivative, nonmonetary notional amount (USD per Mcf)	0.14	[1]

[1]	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.

Fair_Value_Measurements_Additi

Fair Value Measurements (Additional Information) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
	customer	Dec. 31, 2013
Concentration Risk [Line Items]
Impact of ten percent change in commodity prices	$6,700,000
Concentration Risk, Number of Large Customers	2
Largest Oil & Gas Purchasers, One \| Accounts receivable
Concentration Risk [Line Items]
Concentration of credit risk	39.00%
Largest Oil & Gas Purchasers, One \| Total operating revenues
Concentration Risk [Line Items]
Concentration of credit risk	37.00%
Largest Oil & Gas Purchasers, Two \| Accounts receivable
Concentration Risk [Line Items]
Concentration of credit risk	15.00%
Largest Oil & Gas Purchasers, Two \| Total operating revenues
Concentration Risk [Line Items]
Concentration of credit risk	13.00%
Reported Value Measurement
Concentration Risk [Line Items]
Fair value of long-term debt	1,039,000,000	1,643,000,000
Estimate of Fair Value Measurement
Concentration Risk [Line Items]
Fair value of long-term debt	993,700,000	1,650,900,000
Swap [Member] \| Credit Facility
Concentration Risk [Line Items]
Long-term debt	133,000,000
Interest rate	1.04%
Interest rate cash flow hedge liability at fair value	$800,000	$1,800,000

Exploratory_Costs_Capitalized_

Exploratory Costs (Capitalized Exploratory Well Costs) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	well	Dec. 31, 2013	Dec. 31, 2012
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Capitalized exploratory well costs at beginning of period	$57,600	$79,791	$70,437
Additions pending determination of proved reserves	946,751	421,599	406,226
Reclassifications due to determination of proved reserves	-882,254	-442,909	-396,872
Exploratory well costs charged to expense	-2,658	-881	0
Capitalized exploratory well costs at end of period	119,439	57,600	79,791
Exploratory wells in progress	18,781	14,794
Capitalized exploratory well costs for a period of one year or less	100,658	42,481
Capitalized exploratory well costs for a period greater than one year	0	1,206
Total capitalized exploratory well costs	$119,439	$58,481
Wells in process of drilling	38

Reconciliation_of_Earnings_Per2

Reconciliation of Earnings Per Share (Reconciliation) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share Reconciliation
Net income (loss)	$65,418	$457,251	($7,953)	$53,316	$84,093	($19,298)	$83,067	$56,692	$568,032	$204,554	$253,562
Basic Shares Outstanding (in shares)									72,896,579	72,317,865	72,119,021
Earnings Per Share, Basic (dollars per share)	$0.90	$6.26	($0.11)	$0.73	$1.16	($0.27)	$1.15	$0.79	$7.79	$2.83	$3.52
Effect of dilutive securities
Net Income, Diluted EPS	$65,418	$457,251	($7,953)	$53,316	$84,093	($19,298)	$83,067	$56,692	$568,032	$204,554	$253,562
Diluted Shares Outstanding (in shares)									73,274,631	72,470,622	72,316,214
Earnings Per Share, Diluted (dollars per share)	$0.89	$6.22	($0.11)	$0.73	$1.15	($0.27)	$1.15	$0.78	$7.75	$2.82	$3.51
Stock options
Effect of dilutive securities
Incremental Common Shares Attributable to Share-based Payment Arrangements									216,000	112,000	196,000
Non-vested restricted stock
Effect of dilutive securities
Incremental Common Shares Attributable to Share-based Payment Arrangements									58,000	20,000	1,000
Performance share awards
Effect of dilutive securities
Incremental Common Shares Attributable to Share-based Payment Arrangements									104,000	21,000	0

Reconciliation_of_Earnings_Per3

Reconciliation of Earnings Per Share (Antidilutive Securities) (Details)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted EPS (in options or shares)	114	134	850
Non-vested restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted EPS (in options or shares)	3	7	0
Performance share awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted EPS (in options or shares)	2	4	0

Commitments_and_Contingencies_1

Commitments and Contingencies (Additional Information) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014
	pit
Unfavorable Regulatory Action
Site Contingency [Line Items]
Order for payment of additional royalties	$129,700
Preliminary estimates of order maximum liabilities for additional royalties	24,000,000
Mitchell County, Texas
Site Contingency [Line Items]
Environmental Exit Costs, Number of Sites	9
Environmental Exit Costs, Anticipated Cost	2,500,000
Accrual for Environmental Loss Contingencies, Payments	$1,900,000
Crude Oil and Natural Gas [Member]
Site Contingency [Line Items]
Oil and gas delivery commitments, volume	5.4

Commitments_and_Contingencies_2

Commitments and Contingencies (Lease Obligations) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commitments and Contingencies Disclosure [Abstract]
Total lease payments	$24,100,000	$25,000,000	$20,900,000
Operating Leases, Future Minimum Payments Due [Abstract]
2015	2,698,000
2016	2,676,000
2017	2,468,000
2018	2,429,000
2019	2,326,000
2020 and thereafter	$0

Asset_Retirement_Obligations_D

Asset Retirement Obligations (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance of ARO, beginning	$108,533		$118,023		$107,340
Liabilities incurred	2,266		2,772		3,994
Liabilities settled	-1,543		-5,525		-845
Accretion expense	7,859		8,192		7,534
Accretion expense of discontinued operations	251		1,197		1,195
Revision in estimated cash flows	692
Reclassification associated with held for sale properties	-23,747	[1]	-14,929	[2]
Balance of ARO, end	$94,060		$108,533		$118,023

[1]	Asset retirement obligation associated with certain San Juan Basin properties are included as liabilities related to assets held for sale in current liabilities on the balance sheet.
[2]	Asset retirement obligation associated with North Louisiana/East Texas properties are included as liabilities related to assets held for sale in current liabilities on the balance sheet.

Asset_Impairment_Details

Asset Impairment (Details) (USD $)	3 Months Ended	12 Months Ended			3 Months Ended				1 Months Ended
	Mar. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Oct. 31, 2013	Mar. 31, 2014
	Mar. 31, 2012	MMBoe	MMBoe	MMBoe	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Oct. 31, 2013	Mar. 31, 2014
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$21,500,000	$416,801,000	$13,906,000	$6,304,000
Proved developed reserves at end of period (BOE)		264.5	259.8	260.5	264.5		259.8
Total asset impairments from discontinued operations		1,936,000	29,794,000	21,545,000
San Juan Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		236,045,000	0	0
Proved developed reserves at end of period (BOE)		69,043			69,043
San Juan Basin \| Discontinued Operations, Held-for-sale or Disposed of by Sale
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment					88,100,000	147,900,000
Permian Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		55,063,000	13,906,000	6,304,000	55,063,000
North Louisiana/East Texas
Impaired Long-Lived Assets Held and Used [Line Items]
Total asset impairments from discontinued operations		1,936,000	29,794,000	0			5,200,000	24,600,000
Sales price										30,300,000
Natural Gas
Impaired Long-Lived Assets Held and Used [Line Items]
Proved developed reserves at end of period (volume)		589,074	623,305	708,657	589,074		623,305
Natural Gas \| North Louisiana/East Texas
Impaired Long-Lived Assets Held and Used [Line Items]
Proved developed reserves at end of period (volume)			23,000				23,000
Oil Reserves
Impaired Long-Lived Assets Held and Used [Line Items]
Proved developed reserves at end of period (volume)		118,697	113,795	105,976	118,697		113,795
Oil Reserves \| Permian Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		125,693,000	0	0	94,500,000	31,200,000
Oil Reserves \| North Louisiana/East Texas
Impaired Long-Lived Assets Held and Used [Line Items]
Proved developed reserves at end of period (volume)			91				91
Alabama \| Black Warrior Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Cash received from sale of oil properties									160,000,000
Gain on sale of oil and gas property							$35,000,000
Black Warrior Basin \| Natural Gas
Impaired Long-Lived Assets Held and Used [Line Items]
Proved developed reserves at end of period (volume)				97,000

Asset_Impairment_Summary_of_Im

Asset Impairment - Summary of Impairments (Details) (USD $)	3 Months Ended	12 Months Ended			3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Sep. 30, 2014
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$21,500	$416,801	$13,906	$6,304
Total asset impairments from discontinued operations		1,936	29,794	21,545
Total asset impairments		418,737	43,700	27,849
Permian Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		55,063	13,906	6,304	55,063
San Juan Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		236,045	0	0
North Louisiana/East Texas
Impaired Long-Lived Assets Held and Used [Line Items]
Total asset impairments from discontinued operations		1,936	29,794	0		5,200	24,600
East Texas oil and natural gas properties
Impaired Long-Lived Assets Held and Used [Line Items]
Total asset impairments from discontinued operations		0	0	21,545
Oil Reserves \| Permian Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		$125,693	$0	$0	$94,500			$31,200

Acquisition_and_Disposition_of2

Acquisition and Disposition of Properties (Additional Information) (Details) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 21, 2012	1-May-12	Feb. 14, 2012	Dec. 31, 2011	Feb. 28, 2015
	MMBoe	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	MMBoe	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	MMBoe	MMBoe	MMBoe	Feb. 21, 2012	1-May-12	Feb. 14, 2012	MMBoe	Feb. 28, 2015
Significant Acquisitions and Disposals [Line Items]
Proved developed reserves at end of period (BOE)	264.5				259.8				264.5	259.8	260.5
Payments To Acquire Unproved Leasehold Properties									$68,500,000	$26,800,000
Acquisitions, net of cash acquired									-70,730,000	-31,331,000	-139,563,000
Proved Developed And Undeveloped Reserves, Net, Equivalent	372.7				347.8				372.7	347.8	346.4				343.1
Percentage of undeveloped portion of proved reserves									70.00%	45.00%	59.00%
Total revenues	611,435,000	497,761,000	270,097,000	297,278,000	329,962,000	272,038,000	366,981,000	236,331,000	1,679,213,000	1,206,293,000	1,090,948,000
Operating Income (Loss)	94,223,000	48,171,000	3,107,000	31,460,000	74,875,000	17,435,000	138,637,000	21,190,000	176,961,000	252,137,000	364,104,000
February 21, 2012, Reeves County
Significant Acquisitions and Disposals [Line Items]
Net acres												4,829
Percentage of undivided interest												50.00%
Number of wells												3
Cash received from sale of oil properties												18,000,000
February 21, 2012, Reeves County \| Contingent Sales Agreement
Significant Acquisitions and Disposals [Line Items]
Net acres													51,720
Percentage of undivided interest													50.00%
Unproved Leasehold Properties
Significant Acquisitions and Disposals [Line Items]
Purchase price											18,000,000
February 14, 2012, Permian Basin
Significant Acquisitions and Disposals [Line Items]
Purchase price														67,615,000
Proved Developed And Undeveloped Reserves, Net, Equivalent														8.2
Percentage of undeveloped portion of proved reserves														81.00%
Total revenues											11,700,000
Operating Income (Loss)											3,100,000
February 14, 2012, Permian Basin \| Oil Reserves
Significant Acquisitions and Disposals [Line Items]
Percentage of proved reserves acquired														64.00%
February 14, 2012, Permian Basin \| Natural Gas Liquids Reserves
Significant Acquisitions and Disposals [Line Items]
Percentage of proved reserves acquired														22.00%
February 14, 2012, Permian Basin \| Natural Gas Reserves
Significant Acquisitions and Disposals [Line Items]
Percentage of proved reserves acquired														14.00%
December 2012, Permian Basin [Member]
Significant Acquisitions and Disposals [Line Items]
Purchase price											18,700,000
San Juan Basin
Significant Acquisitions and Disposals [Line Items]
Proved developed reserves at end of period (BOE)	69,043								69,043
Payments To Acquire Unproved Leasehold Properties									22,800,000
Net acres	15,000								15,000
Subsequent Event \| San Juan Basin
Significant Acquisitions and Disposals [Line Items]
Sale of assets																$395,000,000

Acquisition_and_Disposition_of3

Acquisition and Disposition of Properties (Permian Basin) (Details) (February 14, 2012, Permian Basin, USD $)	Feb. 14, 2012
In Thousands, unless otherwise specified	Feb. 14, 2012
February 14, 2012, Permian Basin
Significant Acquisitions and Disposals [Line Items]
Cash (net)	$67,615
Recognized amounts of identifiable assets acquired and liabilities assumed
Proved properties	65,581
Unproved leasehold properties	911
Accounts receivable	1,358
Accounts payable	-25
Asset retirement obligation	-210
Total identifiable net assets	$67,615

Discontinued_Operations_Additi

Discontinued Operations (Additional Information) (Details) (USD $)	3 Months Ended	12 Months Ended			0 Months Ended	1 Months Ended	3 Months Ended		0 Months Ended
	Mar. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 02, 2014	Oct. 31, 2013	Dec. 31, 2013	Sep. 30, 2013	Oct. 30, 2012	Mar. 31, 2014	Nov. 17, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on disposal of discontinued operations, net		$724,594,000	$5,605,000	$0
Total asset impairments from discontinued operations		1,936,000	29,794,000	21,545,000
Asset impairment	21,500,000	416,801,000	13,906,000	6,304,000
Natural Gas Reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (volume)		589,074	623,305	708,657			623,305
Oil Reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (volume)		118,697	113,795	105,976			113,795
Black Warrior Basin \| Natural Gas Reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (volume)				97,000
Alabama Gas Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal group, consideration					1,600,000,000
Debt assumed					267,000,000
Proceeds from sale					1,320,000,000
Gain on disposal of discontinued operations, net					726,500,000
Black Warrior Basin \| Alabama
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash received from sale of oil properties						160,000,000
Gain on sale of oil and gas property							35,000,000
North Louisiana/East Texas
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales price										30,300,000
Total asset impairments from discontinued operations		1,936,000	29,794,000	0			5,200,000	24,600,000
North Louisiana/East Texas \| Natural Gas Reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (volume)			23,000				23,000
North Louisiana/East Texas \| Oil Reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (volume)			91				91
Credit Facility, September 2, 2014 \| Syndicated Credit Facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Credit facilities					1,500,000,000						2,000,000,000
Debt instrument, term					5 years
Expiration period					5 years
Credit Facility, October 30, 2012 \| Syndicated Credit Facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Credit facilities									$1,250,000,000
Debt instrument, term									5 years

Discontinued_Operations_Balanc

Discontinued Operations (Balance Sheet) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2014
Assets of Disposal Group, Including Discontinued Operation [Abstract]
Cash	$3,032,000
Accounts receivable	107,849,000	[1]
Inventories	41,268,000
Oil and natural gas properties	348,379,000
Less accumulated depreciation, depletion and amortization	-301,609,000
Utility plant	1,491,433,000
Less accumulated depreciation	-605,924,000
Other property, net	206,000
Other current assets	29,458,000	[1]
Other long-term assets	128,780,000
Total assets held-for-sale	1,242,872,000
Liabilities of Disposal Group, Including Discontinued Operation [Abstract]
Accounts payable	-50,396,000
Royalty payable	-1,419,000
Accrued taxes	-28,027,000
Notes payable to banks	-50,000,000
Other current liabilities	-105,413,000	[1]
Other long-term liabilities	-346,392,000
Long-term debt	-249,923,000
Total liabilities held-for-sale	-831,570,000
Total held-for-sale properties	411,302,000
Adjustment for affiliated companies receivables	4,700,000
Assets reclassified to continuing operations	1,600,000
Liabilities reclassified to continuing operations	500,000
San Juan Basin
Assets of Disposal Group, Including Discontinued Operation [Abstract]
Oil and natural gas properties			1,166,124,000
Less accumulated depreciation, depletion and amortization			-770,327,000
Total assets held-for-sale			395,797,000
Liabilities of Disposal Group, Including Discontinued Operation [Abstract]
Other long-term liabilities			-24,230,000
Total liabilities held-for-sale			-24,230,000
Total held-for-sale properties			371,567,000
Alabama Gas Corporation
Assets of Disposal Group, Including Discontinued Operation [Abstract]
Cash	3,032,000
Accounts receivable	103,748,000	[1]
Inventories	41,200,000
Oil and natural gas properties	0
Less accumulated depreciation, depletion and amortization	0
Utility plant	1,491,433,000
Less accumulated depreciation	-605,924,000
Other property, net	41,000
Other current assets	29,458,000	[1]
Other long-term assets	128,780,000
Total assets held-for-sale	1,191,768,000
Liabilities of Disposal Group, Including Discontinued Operation [Abstract]
Accounts payable	-48,653,000
Royalty payable	0
Accrued taxes	-28,027,000
Notes payable to banks	-50,000,000
Other current liabilities	-105,013,000	[1]
Other long-term liabilities	-331,409,000
Long-term debt	-249,923,000
Total liabilities held-for-sale	-813,025,000
Total held-for-sale properties	378,743,000
Black Warrior Basin
Assets of Disposal Group, Including Discontinued Operation [Abstract]
Cash	0
Accounts receivable	2,829,000	[1]
Inventories	0
Oil and natural gas properties	0
Less accumulated depreciation, depletion and amortization
Utility plant	0
Less accumulated depreciation	0
Other property, net	0
Other current assets	0	[1]
Other long-term assets	0
Total assets held-for-sale	2,829,000
Liabilities of Disposal Group, Including Discontinued Operation [Abstract]
Accounts payable	-1,732,000
Royalty payable	-550,000
Accrued taxes	0
Notes payable to banks	0
Other current liabilities	-379,000	[1]
Other long-term liabilities	0
Long-term debt	0
Total liabilities held-for-sale	-2,661,000
Total held-for-sale properties	168,000
North Louisiana/East Texas
Assets of Disposal Group, Including Discontinued Operation [Abstract]
Cash	0
Accounts receivable	1,272,000	[1]
Inventories	68,000
Oil and natural gas properties	348,379,000
Less accumulated depreciation, depletion and amortization	-301,609,000
Utility plant	0
Less accumulated depreciation	0
Other property, net	165,000
Other current assets	0	[1]
Other long-term assets	0
Total assets held-for-sale	48,275,000
Liabilities of Disposal Group, Including Discontinued Operation [Abstract]
Accounts payable	-11,000
Royalty payable	-869,000
Accrued taxes	0
Notes payable to banks	0
Other current liabilities	-21,000	[1]
Other long-term liabilities	-14,983,000
Long-term debt	0
Total liabilities held-for-sale	-15,884,000
Total held-for-sale properties	$32,391,000

[1]	At December 31, 2013, Alagascoâ€™s accounts receivable included a consolidating adjustment of $4.7 million to adjust for affiliated companies receivables. Certain other current assets and other current liabilities at Alagasco of $1.6 million and $0.5 million, respectively, were reclassified to continuing operations at Energen.

Discontinued_Operations_Income

Discontinued Operations (Income Statement) (Details) (USD $)	3 Months Ended																12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Natural gas distribution revenues																	$397,648	$533,338	$451,589
Oil and natural gas revenues																	5,199	60,191	76,350
DIscontinued operations, total revenues	0	[1]	0	[1]	0	[1]	263,900	[1]	142,771	[1]	48,368	[1]	123,076	[1]	256,348	[1]	402,847	593,529	527,939
Pretax income from discontinued operations																	47,220	92,253	79,197
Income tax expense																	17,928	33,174	30,256
Income from discontinued operations																	29,292	59,079	48,941
Gain on disposal of discontinued operations, net																	724,594	5,605	0
Income tax expense																	285,497	2,011	0
Gain on Disposal of Discontinued Operations, net																	439,097	3,594	0
Income From Discontinued Operations																	$468,389	$62,673	$48,941
Diluted earnings per average common share
Income from discontinued operations																	$0.40	$0.81	$0.68
Gain on disposal of discontinued operations, net																	$5.99	$0.05	$0
Total Income From Discontinued Operations																	$6.39	$0.86	$0.68
Basic earnings per average common share
Income from discontinued operations																	$0.40	$0.82	$0.68
Gain on disposal of discontinued operations, net																	$6.02	$0.05	$0
Total Income From Discontinued Operations																	$6.42	$0.87	$0.68

[1]	As discussed in Note 15, Discontinued Operations and Held for Sale Properties, during the third quarter of 2014, Energen completed the transaction to sell Alagasco to Laclede. During the second quarter of 2014, Energen classified Alagasco as held for sale and reflected the associated operating results in discontinued operations. During the fourth quarter of 2013, Energen completed the sale of its Black Warrior Basin coalbed methane properties in Alabama. The property was classified as held for sale and reflected in discontinued operations during the third quarter of 2013. Also, during the third quarter of 2013, Energen classified its North Louisiana/East Texas natural gas and oil properties as held for sale and reflected the associated operating results in discontinued operations.

Supplemental_Cash_Flow_Informa2

Supplemental Cash Flow Information (Schedule of Supplemental Cash Flow Information) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Cash Flow Information [Abstract]
Interest paid, net of amount capitalized	$32,172	$38,255	$46,224
Income taxes paid	219,505	22,781	18,023
Noncash investing activities:
Accrued development, exploration costs and other capital	207,461	93,623	116,488
Capitalized asset retirement obligations costs	2,958	2,772	3,994
Capital lease obligations	0	0	5,072
Receivable from sale of Alabama Gas Corporation	8,247	0	0
Noncash financing activities:
Issuance of common stock for employee benefit plans	2,448	1,015	838
Treasury stock acquired in connection with tax withholdings	$2,547	$977	$277

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Loss) (Rollforward of Accumulated Other Comprehensive Income (Loss) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 31, 2013	($20,067)
Other comprehensive loss before reclassifications	-5,317
Amounts reclassified from accumulated other comprehensive income (loss)	2,514
Change in accumulated other comprehensive income (loss)	-2,803
Balance as of December 31, 2014	-22,870
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 31, 2013	12,178
Other comprehensive loss before reclassifications	-261
Amounts reclassified from accumulated other comprehensive income (loss)	-11,917
Change in accumulated other comprehensive income (loss)	-12,178
Balance as of December 31, 2014	0
Pension and Postretirement Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance as of December 31, 2013	-32,245
Other comprehensive loss before reclassifications	-5,056
Amounts reclassified from accumulated other comprehensive income (loss)	14,431
Change in accumulated other comprehensive income (loss)	9,375
Balance as of December 31, 2014	($22,870)

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Income (Loss) (Reclassifications of Accumulated Other Comprehensive Income) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Gains (losses) on cash flow hedges:
Operating revenue	$611,435,000	$497,761,000	$270,097,000	$297,278,000	$329,962,000	$272,038,000	$366,981,000	$236,331,000	$1,679,213,000		$1,206,293,000		$1,090,948,000
Interest expense									-37,771,000		-39,736,000		-47,565,000
Pension and postretirement plans:
Income tax expense									-40,728,000		-74,323,000		-113,563,000
Settlement charges				6,900,000
Settlement charges expensed				3,700,000
Nonqualified Supplemental Retirement Plans
Pension and postretirement plans:
Settlement charges	1,800,000	26,000		400,000		64,000		500,000
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements						18,000
Settlement charges expensed								100,000
Alabama Gas Corporation \| Nonqualified Supplemental Retirement Plans
Pension and postretirement plans:
Settlement charges						46,000		400,000
Reclassification out of Accumulated Other Comprehensive Income
Pension and postretirement plans:
Net of tax									-2,514,000		12,324,000
Reclassification out of Accumulated Other Comprehensive Income \| Cash Flow Hedges
Pension and postretirement plans:
Income From Continuing Operations									19,331,000		33,961,000
Income tax expense									-7,414,000		-12,957,000
Net of tax									11,917,000		21,004,000
Reclassification out of Accumulated Other Comprehensive Income \| Pension and Postretirement Plans
Pension and postretirement plans:
Transition obligation									-22,000		-319,000
Prior service cost									-248,000		-257,000
Actuarial losses									-21,932,000	[1]	-12,357,000	[1]
Actuarial losses on settlement charges									0	[1]	-421,000	[1]
Income From Continuing Operations									-22,202,000		-13,354,000
Income tax expense									7,771,000		4,674,000
Net of tax									-14,431,000		-8,680,000
Reclassification out of Accumulated Other Comprehensive Income \| Commodity Contract \| Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax									21,611,000		35,684,000
Reclassification out of Accumulated Other Comprehensive Income \| Interest Rate Swap \| Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax									$2,280,000		$1,723,000

[1]	In the first quarter of 2013, Energen incurred a settlement charge of $0.5 million for the payment of lump sums from the nonqualified supplemental retirement plans, of which $0.1 million was recognized in actuarial losses above and $0.4 million was recognized as a regulatory asset at Alagasco and reported in actuarial losses on settlement charges above. In the third quarter of 2013, Energen incurred a settlement charge of $64,000 for the payment of lump sums from the nonqualified supplemental retirement plans, of which $18,000 was recognized in actuarial losses above and $46,000 was recognized as a regulatory asset at Alagasco and reported in actuarial losses on settlement charges above.

Summarized_Quarterly_Financial2

Summarized Quarterly Financial Data (Unaudited) (Quarterly Operating Results) (Details) (USD $)	3 Months Ended																12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Selected Quarterly Financial Information [Abstract]
Total revenues	$611,435		$497,761		$270,097		$297,278		$329,962		$272,038		$366,981		$236,331		$1,679,213	$1,206,293	$1,090,948
Discontinued operations	0	[1]	0	[1]	0	[1]	-263,900	[1]	-142,771	[1]	-48,368	[1]	-123,076	[1]	-256,348	[1]	-402,847	-593,529	-527,939
Operating income (loss)	94,223		48,171		3,107		31,460		74,875		17,435		138,637		21,190		176,961	252,137	364,104
Discontinued operations	0	[1]	0	[1]	0	[1]	-73,139	[1]	-35,755	[1]	21,487	[1]	-7,667	[1]	-84,146	[1]
Income From Continuing Operations	66,519		20,631		-3,154		15,647		45,633		5,407		82,422		8,419		99,643	141,881	204,621
Net income (loss)	65,418		457,251		-7,953		53,316		84,093		-19,298		83,067		56,692		568,032	204,554	253,562
Diluted earnings per average common share
Continuing operations (in dollars per share)	$0.91		$0.28		($0.04)		$0.21		$0.62		$0.07		$1.14		$0.12		$1.36	$1.96	$2.83
Net income (loss) (in dollars per share)	$0.89		$6.22		($0.11)		$0.73		$1.15		($0.27)		$1.15		$0.78		$7.75	$2.82	$3.51
Basic earnings per average common share
Continuing operations (in dollars per share)	$0.91		$0.28		($0.04)		$0.22		$0.63		$0.07		$1.14		$0.12		$1.37	$1.96	$2.84
Net income (loss) (in dollars per share)	$0.90		$6.26		($0.11)		$0.73		$1.16		($0.27)		$1.15		$0.79		$7.79	$2.83	$3.52
Originally reported
Selected Quarterly Financial Information [Abstract]
Total revenues	611,435		497,761		270,097		561,178		472,733		320,406		490,057		492,679
Operating income (loss)	$94,223		$48,171		$3,107		$104,599		$110,630		($4,052)		$146,304		$105,336

[1]	As discussed in Note 15, Discontinued Operations and Held for Sale Properties, during the third quarter of 2014, Energen completed the transaction to sell Alagasco to Laclede. During the second quarter of 2014, Energen classified Alagasco as held for sale and reflected the associated operating results in discontinued operations. During the fourth quarter of 2013, Energen completed the sale of its Black Warrior Basin coalbed methane properties in Alabama. The property was classified as held for sale and reflected in discontinued operations during the third quarter of 2013. Also, during the third quarter of 2013, Energen classified its North Louisiana/East Texas natural gas and oil properties as held for sale and reflected the associated operating results in discontinued operations.

Oil_and_Natural_Gas_Operations2

Oil and Natural Gas Operations (Unaudited) (Capitalized Costs) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Oil and Gas Exploration and Production Industries Disclosures [Abstract]
Proved	$8,069,638	$7,043,779
Unproved	142,340	168,975
Total capitalized costs	8,211,978	7,212,754
Accumulated depreciation, depletion and amortization	2,663,434	2,078,411
Capitalized costs, net	$5,548,544	$5,134,343

Oil_and_Natural_Gas_Operations3

Oil and Natural Gas Operations (Unaudited) (Costs Incurred) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property acquisition:
Proved	$2,582	$4,661	$79,862
Unproved	68,514	26,820	58,634
Exploration	972,164	435,636	419,284
Development	408,949	655,353	749,256
Total costs incurred	$1,452,209	$1,122,470	$1,307,036

Oil_and_Natural_Gas_Operations4

Oil and Natural Gas Operations (Unaudited) (Results of Operations) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Oil and Gas Exploration and Production Industries Disclosures [Abstract]
Gross revenues	$1,679,213	[1]	$1,206,293	[1]	$1,090,948	[1]
Production (lifting costs)	376,495		351,541		278,193
Exploration expense	28,090		14,036		13,052
Depreciation, depletion and amortization including asset impairments	960,539		463,606		345,873
Accretion expense	7,608		6,995		6,339
Income tax expense	99,469		128,773		160,551
Results of operations from producing activities	$207,012		$241,342		$286,940

[1]	The years ended December 31, 2014, 2013 and 2012 gross revenues include a pre-tax non-cash mark-to-market gain on derivatives of $315.4 million, a pre-tax non-cash mark-to-market loss on derivatives of $47.8 million and a pre-tax non-cash mark-to-market gain on derivatives of $58.8 million, respectively.

Oil_and_Natural_Gas_Operations5

Oil and Natural Gas Operations (Unaudited) (Oil and Gas Operations) (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	MMBoe	MMBoe	MMBoe
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves at beginning of period, total	347.8	346.4	343.1
Revisions of previous estimates, total	-75.7	4.6	-42.1
Purchases, total	0.1	0.2	12.4
Extensions and discoveries, total	130	36.8	57.1
Production, total	-25.8	-25.4	-24.1
Sales, total	-3.7	-14.8
Proved reserves at end of period, total	372.7	347.8	346.4
Proved developed reserves at end of period (BOE)	264.5	259.8	260.5
Proved undeveloped reserves at end of period (BOE)	108.2	88	85.9
Oil Reserves
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves at beginning of period	164,870	155,348	129,578
Revisions of previous estimates	-48,548	-680	-8,546
Purchases	88	142	7,950
Extensions and discoveries	76,722	20,517	35,132
Production	-11,818	-10,378	-8,766
Sales	-87	-79
Proved reserves at end of period	181,227	164,870	155,348
Proved developed reserves at end of period (volume)	118,697	113,795	105,976
Proved undeveloped reserves at end of period (volume)	62,530	51,075	49,372
Natural Gas Liquids Reserves
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves at beginning of period	63,011	56,155	53,957
Revisions of previous estimates	-15,165	2,211	-9,557
Purchases	26	56	2,569
Extensions and discoveries	29,695	7,823	11,759
Production	-4,104	-3,233	-2,573
Sales	0	-1
Proved reserves at end of period	73,463	63,011	56,155
Proved developed reserves at end of period (volume)	47,621	42,087	36,440
Proved undeveloped reserves at end of period (volume)	25,842	20,924	19,715
Natural Gas Reserves
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves at beginning of period	719,725	809,128	957,368
Revisions of previous estimates	-71,806	18,465	-143,704
Purchases	116	282	10,656
Extensions and discoveries	141,209	50,568	61,170
Production	-59,562	-70,506	-76,362
Sales	-21,756	-88,212
Proved reserves at end of period	707,926	719,725	809,128
Proved developed reserves at end of period (volume)	589,074	623,305	708,657
Proved undeveloped reserves at end of period (volume)	118,852	96,420	100,471

Oil_and_Natural_Gas_Operations6

Oil and Natural Gas Operations (Unaudited) (Oil and Gas Operations, Activities) (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	MMBoe	MMBoe	MMBoe
Reserve Quantities [Line Items]
Reserves included in engineer estimates, percent	99.00%
Revisions of previous estimates	-75.7	4.6	-42.1
Purchases	0.1	0.2	12.4
Extensions and discoveries	130	36.8	57.1
Percentage of undeveloped portion of proved reserves	70.00%	45.00%	59.00%
Percentage of developed portion of proved reserves	30.00%	55.00%	41.00%
Sales	3.7	14.8
Extension Drilling
Reserve Quantities [Line Items]
Extensions and discoveries	89.6	21.6	45.6
Exploratory Drilling
Reserve Quantities [Line Items]
Extensions and discoveries	40.4	15.2	11.5
Price Related Revisions
Reserve Quantities [Line Items]
Revisions of previous estimates	3.9	7
No Longer Expected to be Drilled
Reserve Quantities [Line Items]
Revisions of previous estimates		-5.3
No Longer Expected to Be Drilled Beyond Five Years
Reserve Quantities [Line Items]
Revisions of previous estimates	-53.4	-4.6
San Juan Basin
Reserve Quantities [Line Items]
Revisions of previous estimates	1.6	2.2	-19.7
Extensions and discoveries	1.1	2.3	0.9
Number of well locations	16		6
Proved Developed and Undeveloped Reserves, Pay-Add Locations	10	30
San Juan Basin \| Price Related Revisions
Reserve Quantities [Line Items]
Revisions of previous estimates	4.4	5.9
San Juan Basin \| Higher Operating Costs
Reserve Quantities [Line Items]
Revisions of previous estimates	-1.5
San Juan Basin \| No Longer Expected to be Drilled
Reserve Quantities [Line Items]
Revisions of previous estimates		-4.6
San Juan Basin \| Change in Year-End Pricing Revisions
Reserve Quantities [Line Items]
Revisions of previous estimates			-22.5
Permian Basin
Reserve Quantities [Line Items]
Revisions of previous estimates	-77.3	1.2	-15.8
Extensions and discoveries	128.6	34.4	56.1
Number of well locations	361	262	422
Permian Basin \| Price Related Revisions
Reserve Quantities [Line Items]
Revisions of previous estimates		0.4	-1
Permian Basin \| Higher Operating Costs
Reserve Quantities [Line Items]
Revisions of previous estimates	-5.4
Permian Basin \| Reclassifying as Unproved
Reserve Quantities [Line Items]
Revisions of previous estimates	-53.4
Permian Basin \| Well Performance Revisions
Reserve Quantities [Line Items]
Revisions of previous estimates	-13.3
Permian Basin \| No Longer Expected to be Drilled
Reserve Quantities [Line Items]
Revisions of previous estimates		-0.7
Permian Basin \| Change in Year-End Pricing Revisions
Reserve Quantities [Line Items]
Revisions of previous estimates	-0.5
North Louisiana and East Texas Natural Gas and Oil Properties [Member]
Reserve Quantities [Line Items]
Sales	3.7
Black Warrior Basin
Reserve Quantities [Line Items]
Revisions of previous estimates			-5.1
Sales		14.8
Black Warrior Basin \| Change in Year-End Pricing Revisions
Reserve Quantities [Line Items]
Revisions of previous estimates			-5.9

Oil_and_Natural_Gas_Operations7

Oil and Natural Gas Operations (Unaudited) (Standardized Measure of Discounted Future Net Cash Flows) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Oil and Gas Exploration and Production Industries Disclosures [Abstract]
Deferred hedging gain (loss) excluded from calculation of standardized measure of future net cash flows	$315,400,000		$21,600,000		$74,800,000
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Standardized Measure [Abstract]
Future gross revenues	20,971,672,000		19,509,305,000		17,735,363,000
Future production costs	7,532,273,000		6,136,709,000		5,715,248,000
Future development costs	1,784,738,000		1,896,602,000		1,892,600,000
Future income tax expense	3,440,582,000		3,209,697,000		2,809,411,000
Future net cash flows	8,214,079,000		8,266,297,000		7,318,104,000
Discount at 10% per annum	3,994,423,000		4,248,456,000		3,618,785,000
Standardized measure of discounted future net cash flows relating to proved oil and natural gas reserves	4,219,656,000		4,017,841,000		3,699,319,000
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]
Balance at beginning of year	4,017,841,000		3,699,319,000		3,629,163,000
Revisions to reserves proved in prior years:
Net changes in prices, production costs and future development costs	-1,147,028,000		566,838,000		-922,792,000
Net changes due to revisions in quantity estimates	-1,285,394,000		-81,762,000		-383,755,000
Development costs incurred, previously estimated	337,198,000		299,432,000		472,603,000
Accretion of discount	401,784,000		369,932,000		362,916,000
Changes in timing and other	987,652,000	[1]	-179,502,000	[1]	-317,244,000	[1]
Total revisions	-705,788,000		974,938,000		-788,272,000
New field discoveries and extensions, net of future production and development costs	2,321,028,000		376,326,000		1,025,419,000
Sales of oil and gas produced, net of production costs	-1,054,553,000		-1,014,593,000		-812,781,000
Purchases	4,241,000		4,690,000		189,755,000
Sales	-21,092,000		-24,876,000		0
Net change in income taxes	-342,021,000		2,037,000		456,035,000
Net change in standardized measure of discounted future net cash flows	201,815,000		318,522,000		70,156,000
Balance at end of year	$4,219,656,000		$4,017,841,000		$3,699,319,000

[1]	Amount represents changes in production timing and other. For 2014, the production timing is significantly affected by changes related to the acceleration of the horizontal drilling program and the delay of the vertical drilling program.