Athlon Energy (ATHL) 10-Q 14 Nov 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Nov. 14, 2013
Document and Entity Information	'	'
Entity Registrant Name	'Athlon Energy Inc.	'
Entity Central Index Key	'0001574648	'
Document Type	'10-Q	'
Document Period End Date	30-Sep-13	'
Amendment Flag	'false	'
Current Fiscal Year End Date	'--12-31	'
Entity Current Reporting Status	'Yes	'
Entity Filer Category	'Non-accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	82,129,089
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'Q3	'

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$196,888	$8,871
Accounts receivable	45,851	24,501
Derivatives, at fair value	'	2,246
Inventory	972	1,022
Other	1,205	2,486
Total current assets	244,916	39,126
Properties and equipment, at cost - full cost method:	'	'
Proved properties, including wells and related equipment	1,084,881	788,571
Unproved properties	110,095	89,860
Accumulated depletion, depreciation, and amortization	-135,689	-73,824
Properties and equipment, net	1,059,287	804,607
Derivatives, at fair value	1,211	2,854
Debt issuance costs	14,603	4,418
Other	1,400	1,293
Total assets	1,321,417	852,298
Accounts payable:	'	'
Trade	2,338	3,170
Affiliate	2	935
Accrued liabilities:	'	'
Lease operating	5,391	3,858
Production, severance, and ad valorem taxes	5,362	1,307
Development capital	60,092	39,483
Interest	16,802	834
Derivatives, at fair value	10,185	592
Revenue payable	19,550	9,330
Deferred taxes	14,529	58
Other	2,021	1,808
Total current liabilities	136,272	61,375
Derivatives, at fair value	992	519
Asset retirement obligations, net of current portion	6,439	5,049
Long-term debt	500,000	362,000
Deferred taxes	67,878	2,340
Other	109	138
Total liabilities	711,690	431,421
Commitments and contingencies	'	'
Equity:	'	'
Partners' equity	'	420,877
Preferred stock, $.01 par value, at September 30, 2013, 50,000,000 shares authorized, none issued and outstanding	'	'
Common stock, $.01 par value, at September 30, 2013, 500,000,000 shares authorized, 82,189,089 issued and outstanding	821	'
Additional paid-in capital	588,583	'
Retained earnings	10,278	'
Total stockholders' equity	599,682	'
Noncontrolling interest	10,045	'
Total equity	609,727	420,877
Total liabilities and equity	$1,321,417	$852,298

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Sep. 30, 2013
CONSOLIDATED BALANCE SHEETS	'
Preferred stock, par value (in dollars per share)	$0.01
Preferred stock, shares authorized	50,000,000
Preferred stock, shares issued	0
Preferred stock, shares outstanding	0
Common stock, par value (in dollars per share)	$0.01
Common stock, shares authorized	500,000,000
Common stock, shares issued	82,189,089
Common stock, shares outstanding	82,189,089

CONSOLIDATED_STATEMENTS_OF_OPE

CONSOLIDATED STATEMENTS OF OPERATIONS (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues:	'	'	'	'
Oil	$75,666	$34,357	$175,934	$91,407
Natural gas	4,164	2,383	11,894	5,323
Natural gas liquids	8,595	5,346	20,508	14,379
Total revenues	88,425	42,086	208,336	111,109
Production:	'	'	'	'
Lease operating	8,762	7,205	23,774	17,846
Production, severance, and ad valorem taxes	5,439	2,806	13,380	7,617
Processing, gathering, and overhead	59	29	169	55
Depletion, depreciation, and amortization	23,611	15,091	62,022	37,770
General and administrative	6,725	2,134	13,723	7,212
Contract termination fee	2,408	'	2,408	'
Derivative fair value loss (gain)	27,037	14,268	21,331	-9,590
Accretion of discount on asset retirement obligations	174	123	485	343
Total expenses	74,215	41,656	137,292	61,253
Operating income	14,210	430	71,044	49,856
Other income (expenses):	'	'	'	'
Interest	-10,039	-2,602	-26,595	-5,804
Other	30	'	30	2
Total other expenses	-10,009	-2,602	-26,565	-5,802
Income (loss) before income taxes	4,201	-2,172	44,479	44,054
Income tax provision (benefit)	1,934	-76	6,805	1,546
Consolidated net income (loss)	2,267	-2,096	37,674	42,508
Less: net income (loss) attributable to noncontrolling interest	-215	'	616	'
Net income (loss) attributable to stockholders	$2,482	($2,096)	$37,058	$42,508
Net income (loss) per common share:	'	'	'	'
Basic (in dollars per share)	$0.03	($0.03)	$0.53	$0.64
Diluted (in dollars per share)	$0.03	($0.03)	$0.53	$0.62
Weighted average common shares outstanding:	'	'	'	'
Basic (in shares)	76,637	66,340	69,810	66,340
Diluted (in shares)	78,493	66,340	71,666	68,196

CONSOLIDATED_STATEMENT_OF_CHAN

CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (USD $)	Total	Total Stockholders' Equity	Partners' Equity	Common Stock	Additional Paid-in Capital	Retained Earnings	Noncontrolling Interest
Balance at Dec. 31, 2012	$420,877,000	'	$420,877,000	'	'	'	'
Balance at Dec. 31, 2012	420,877,000	'	'	'	'	'	'
Increase (Decrease) in Equity	'	'	'	'	'	'	'
Capital contributions	1,500,000	'	1,500,000	'	'	'	'
Equity-based compensation prior to corporate reorganization	89,000	'	89,000	'	'	'	'
Net income prior to corporate reorganization	26,780,000	'	26,780,000	'	'	'	'
Distributions to Athlon Holdings LP's Class A limited partners	-75,000,000	'	-75,000,000	'	'	'	'
Common stock issued in corporate reorganization	'	364,817,000	-374,246,000	663,000	364,154,000	'	9,429,000
Common stock issued in corporate reorganization (in shares)	'	'	'	66,340,000	'	'	'
Tax impact of corporate reorganization	-73,204,000	-73,204,000	'	'	-73,204,000	'	'
Equity-based compensation subsequent to corporate reorganization	2,160,000	2,160,000	'	'	2,160,000	'	'
Shares of common stock sold in initial public offering, net of offering costs	295,631,000	295,631,000	'	158,000	295,473,000	'	'
Shares of common stock sold in initial public offering, net of offering costs (in shares)	'	'	'	15,789,000	'	'	'
Consolidated net income subsequent to corporate reorganization	10,894,000	10,278,000	'	'	'	10,278,000	616,000
Balance at Sep. 30, 2013	$609,727,000	$599,682,000	'	$821,000	$588,583,000	$10,278,000	$10,045,000
Balance (in shares) at Sep. 30, 2013	82,189,089	'	'	82,129,000	'	'	'

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:	'	'
Consolidated net income	$37,674	$42,508
Adjustments to reconcile consolidated net income to net cash provided by operating activities:	'	'
Depletion, depreciation, and amortization	62,022	37,770
Deferred taxes	6,805	1,546
Non-cash derivative loss (gain)	13,955	-11,760
Equity-based compensation	1,799	118
Other	4,756	952
Changes in operating assets and liabilities, net of effects from acquisitions:	'	'
Accounts receivable	-21,350	-7,390
Other current assets	-155	-975
Accounts payable	-702	-461
Accrued interest	15,968	478
Revenue payable	9,718	3,317
Other current liabilities	6,285	-3,349
Net cash provided by operating activities	136,775	62,754
Cash flows from investing activities:	'	'
Acquisitions of oil and natural gas properties	-36,533	-3,290
Development of oil and natural gas properties	-257,984	-183,327
Other	-486	-283
Net cash used in investing activities	-295,003	-186,900
Cash flows from financing activities:	'	'
Proceeds from long-term debt, net of issuance costs	629,627	425,684
Payments on long-term debt	-505,926	-325,000
Distributions to Athlon Holdings LP's Class A limited partners	-75,000	'
Shares of common stock sold in initial public offering, net of offering costs	296,044	'
Other	1,500	166
Net cash provided by financing activities	346,245	100,850
Increase (decrease) in cash and cash equivalents	188,017	-23,296
Cash and cash equivalents, beginning of period	8,871	32,030
Cash and cash equivalents, end of period	$196,888	$8,734

Formation_of_the_Company_and_D

Formation of the Company and Description of Business	9 Months Ended
	Sep. 30, 2013
Formation of the Company and Description of Business	'
Formation of the Company and Description of Business	'
	Note 1.         Formation of the Company and Description of Business
	Athlon Energy Inc. (together with its subsidiaries, “Athlon”), a Delaware corporation, was formed on April 1, 2013 and is an independent exploration and production company focused on the acquisition, development, and exploitation of unconventional oil and liquids-rich natural gas reserves in the Permian Basin.
	On April 26, 2013, Athlon Holdings LP (together with its subsidiaries, “Holdings”), a Delaware limited partnership, underwent a corporate reorganization and as a result, Holdings became a majority-owned subsidiary of Athlon.  Holdings is considered Athlon’s accounting predecessor.  Athlon operates and controls all of the business and affairs of Holdings and consolidates its financial results.  Holdings is not subject to federal income taxes.  On the date of the corporate reorganization, a corresponding “first day” net deferred tax liability of approximately $73.2 million was recorded for differences between the tax and book basis of Athlon’s assets and liabilities.  The offset of the deferred tax liability was recorded to additional paid-in capital.
	Prior to the corporate reorganization, Holdings was a party to a limited partnership agreement with its management group and Apollo Athlon Holdings, LP (“Apollo”), which is an affiliate of Apollo Global Management, LLC.  Prior to the corporate reorganization, Apollo Investment Fund VII, L.P. and its parallel funds (the “Apollo Funds”), members of Holdings’ management team, and certain employees owned all of the Class A limited partner interests in Holdings and members of Holdings’ management team and certain employees owned all of the Class B limited partner interests in Holdings.
	In the corporate reorganization, the Apollo Funds entered into a number of distribution and contribution transactions pursuant to which the Apollo Funds exchanged their Class A limited partner interests in Holdings for common stock of Athlon.  The remaining holders of Class A limited partner interests in Holdings have not exchanged their interests in the reorganization transactions.  In addition, the holders of the Class B limited partner interests in Holdings exchanged their interests for common stock of Athlon subject to the same conditions and vesting terms.
	Initial Public Offering
	On August 7, 2013, Athlon completed its initial public offering (“IPO”) of 15,789,474 shares of its common stock at $20.00 per share and received net proceeds of approximately $295.6 million, after deducting underwriting discounts and commissions and offering expenses.  Upon closing of the IPO, the limited partnership agreement of Holdings was amended and restated to, among other things, modify Holdings’ capital structure by replacing its different classes of interests with a single new class of units, the “New Holdings Units”.  The members of Holdings’ management team and certain employees that held Class A limited partner interests now own 1,855,563 New Holdings Units and entered into an exchange agreement under which (subject to the terms of the exchange agreement) they have the right to exchange their New Holdings Units for shares of common stock of Athlon on a one-for-one basis, subject to customary conversion rate adjustments for stock splits, stock dividends, and reclassifications.  All other New Holdings Units are held by Athlon.  Athlon used the net proceeds from the IPO to purchase New Holdings Units from Holdings.  Holdings used the proceeds it received as a result of Athlon’s purchase of New Holdings Units (i) to reduce outstanding borrowings under its credit agreement, (ii) to provide additional liquidity for use in its drilling program, and (iii) for general corporate purposes, including potential acquisitions.

Basis_of_Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2013
Basis of Presentation	'
Basis of Presentation	'
	Note 2.         Basis of Presentation
	Athlon’s consolidated financial statements include the accounts of its wholly owned and majority-owned subsidiaries.  All material intercompany balances and transactions have been eliminated in consolidation.
	In the opinion of management, the accompanying unaudited consolidated financial statements include all adjustments necessary to present fairly, in all material respects, Athlon’s financial position as of September 30, 2013, results of operations for the three and nine months ended September 30, 2013 and 2012, and cash flows for the nine months ended September 30, 2013 and 2012.  All adjustments are of a normal recurring nature.  These interim results are not necessarily indicative of results for an entire year.
	Certain amounts and disclosures have been condensed and omitted from the unaudited consolidated financial statements pursuant to the rules and regulations of the United States Securities and Exchange Commission (the “SEC”).  Therefore, these unaudited consolidated financial statements should be read in conjunction with Holdings’ audited consolidated financial statements and related notes thereto included in Athlon’s final prospectus dated August 1, 2013 and filed with the SEC pursuant to Rule 424(b)(4) of the Securities Act of 1933, as amended, on August 5, 2013.
	Income Taxes
	Athlon accounts for income taxes using the asset and liability method.  Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards.  Deferred tax assets and liabilities are measured using enacted tax laws and rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled.  The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date.
	Athlon periodically assesses whether it is more likely than not that it will generate sufficient taxable income to realize its deferred income tax assets, including net operating losses.  In making this determination, Athlon considers all available positive and negative evidence and makes certain assumptions.  Athlon considers, among other things, its deferred tax liabilities, the overall business environment, its historical earnings and losses, current industry trends, and its outlook for future years.  Athlon believes it is more likely than not that certain net operating losses can be carried forward and utilized.
	In April 2013, Athlon had a corporate reorganization to effectuate its IPO.  Holdings, Athlon’s accounting predecessor, is a partnership not subject to federal income tax.  Pursuant to the steps of the corporate reorganization, certain Class A limited partners and the Class B limited partners of Holdings exchanged their interests for shares of Athlon’s common stock.  Athlon’s operations are now subject to federal income tax.  The tax implications of the corporate reorganization and the tax impact of the conversion to operating as a taxable entity have been reflected in the accompanying consolidated financial statements.
	Noncontrolling Interest
	As of September 30, 2013, management and employees owned approximately 2.2% of Holdings.  Athlon owns 100% of Athlon Holdings GP LLC, which is Holdings’ general partner.  Considering the presumption of control, Athlon has fully consolidated the financial position, results of operations, and cash flows of Holdings.
	As presented in the accompanying Consolidated Balance Sheets, “Noncontrolling interest” as of September 30, 2013 of approximately $10.0 million represents management and employees’ 1,855,563 New Holdings Units that are exchangeable for shares of Athlon’s common stock on a one-for-one basis.  As presented in the accompanying Consolidated Statements of Operations, “Net income (loss) attributable to noncontrolling interest” for the three and nine months ended September 30, 2013 of approximately $(0.2) million and $0.6 million, respectively, represents the net income of Holdings attributable to management and employees since April 26, 2013.
	The following table summarizes the effects of changes in Athlon’s partnership interest in Holdings on Athlon’s equity for the periods indicated:
		Three		Nine months
		months		ended
		ended		September
		September		30, 2013
		30, 2013
		(in thousands)
	Net income attributable to stockholders	$	2,482	$	37,058
	Transfer from noncontrolling interest:
	Increase in Athlon’s paid-in capital for corporate reorganization	—		290,950
	Increase in Athlon’s paid-in capital for issuance of 15,789,474 shares of common stock in initial public offering	295,473		295,473
	Net transfer from noncontrolling interest	295,473		586,423
	Change from net income attributable to stockholders and transfers from (to) noncontrolling interest	$	297,955	$	623,481
	New Accounting Pronouncements
	In December 2011, the Financial Accounting Standards Board issued Accounting Standards Update (“ASU”) 2011-11, “Disclosures about Offsetting Assets and Liabilities” and in January 2013 issued ASU 2013-01, “Clarifying the Scope of Disclosures About Offsetting Assets and Liabilities”.  These ASUs created new disclosure requirements regarding the nature of an entity’s rights of setoff and related arrangements associated with its derivative instruments, repurchase agreements, and securities lending transactions.  Certain disclosures of the amounts of certain instruments subject to enforceable master netting arrangements are required, irrespective of whether the entity has elected to offset those instruments in the statement of financial position.  These ASUs were effective retrospectively for annual reporting periods beginning on or after January 1, 2013.  The adoption of these ASUs did not impact Athlon’s financial position, results of operations, or liquidity.
	No other new accounting pronouncements issued or effective from January 1, 2013 through the date of this Report, had or are expected to have a material impact on Athlon’s unaudited consolidated financial statements.

Proved_Properties

Proved Properties	9 Months Ended
	Sep. 30, 2013
Proved Properties	'
Proved Properties	'
	Note 3. Proved Properties
	Amounts shown in the accompanying Consolidated Balance Sheets as “Proved properties, including wells and related equipment” consisted of the following as of the dates indicated:
		September 30,		December 31,
		2013		2012
		(in thousands)
	Proved leasehold costs	$	411,657	$	376,271
	Wells and related equipment - Completed	634,980		379,036
	Wells and related equipment - In process	38,244		33,264
	Total proved properties	$	1,084,881	$	788,571

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2013
Fair Value Measurements	'
Fair Value Measurements	'
	Note 4.  Fair Value Measurements
	The book values of cash and cash equivalents, accounts receivable, and accounts payable approximate fair value due to the short-term nature of these instruments.  Commodity derivative contracts are marked-to-market each quarter and are thus stated at fair value in the accompanying Consolidated Balance Sheets.  As of September 30, 2013, the fair value of the senior notes was approximately $515.6 million using open market quotes (“Level 1” input).
	Derivative Policy
	Athlon uses various financial instruments for non-trading purposes to manage and reduce price volatility and other market risks associated with its oil production.  These arrangements are structured to reduce Athlon’s exposure to commodity price decreases, but they can also limit the benefit Athlon might otherwise receive from commodity price increases.  Athlon’s risk management activity is generally accomplished through over-the-counter commodity derivative contracts with large financial institutions, most of which are lenders underwriting Holdings’ credit agreement.
	Athlon applies the provisions of the “Derivatives and Hedging” topic of the Accounting Standards Codification, which requires each derivative instrument to be recorded in the accompanying Consolidated Balance Sheets at fair value.  If a derivative has not been designated as a hedge or does not otherwise qualify for hedge accounting, it must be adjusted to fair value through earnings.  Athlon elected not to designate its current portfolio of commodity derivative contracts as hedges for accounting purposes.  Therefore, changes in fair value of these derivative instruments are recognized in earnings and included in “Derivative fair value loss (gain)” in the accompanying Consolidated Statements of Operations.
	Athlon enters into commodity derivative contracts for the purpose of economically fixing the price of its anticipated oil production even though Athlon does not designate the derivatives as hedges for accounting purposes.  Athlon classifies cash flows related to derivative contracts based on the nature and purpose of the derivative.  As the derivative cash flows are considered an integral part of Athlon’s oil and natural gas operations, they are classified as cash flows from operating activities in the accompanying Consolidated Statements of Cash Flows.
	Commodity Derivative Contracts
	Commodity prices are often subject to significant volatility due to many factors that are beyond Athlon’s control, including but not limited to: prevailing economic conditions, supply and demand of hydrocarbons in the marketplace, actions by speculators, and geopolitical events such as wars or natural disasters.  Athlon manages oil price risk with swaps and collars.  Swaps provide a fixed price for a notional amount of sales volumes.  Collars provide a floor price on a notional amount of sales volumes while allowing some additional price participation if the relevant index price closes above the floor price.  This participation is limited by a ceiling price specified in the contract.
	The following table summarizes Athlon’s open commodity derivative contracts as of September 30, 2013:
		Average		Weighted -			Average		Weighted -			Average		Weighted -		Asset
		Daily		Average			Daily		Average			Daily		Average		(Liability)
		Floor		Floor			Cap		Cap			Swap		Swap		Fair Market
	Period	Volume		Price			Volume		Price			Volume		Price		Value
		(Bbl)		(per Bbl)			(Bbl)		(per Bbl)			(Bbl)		(per Bbl)		(in thousands)
	Oct. - Dec. 2013	150		$	75		150		$	105.95		7,000		$	95.01	$	(4,205	)
	2014	—		—			—		—			7,950		92.67		(7,532		)
	2015	—		—			—		—			1,300		93.18		2,101
																$	(9,636	)
	Athlon is also a party to Midland-Cushing basis differential swaps for 5,000 Bbls/D at $1.20/Bbl for the fourth quarter of 2013.  At September 30, 2013, the fair value of these contracts was a liability of approximately $0.3 million.
	Counterparty Risk.  At September 30, 2013, Athlon had committed 10% or greater (in terms of fair market value) of its oil derivative contracts in asset positions from the following counterparties, or their affiliates:
		Fair Market Value of
		Oil Derivative
		Contracts
	Counterparty	Committed
		(in thousands)
	BNP Paribas	$	458
	Athlon does not require collateral from its counterparties for entering into financial instruments, so in order to mitigate the credit risk associated with financial instruments, Athlon enters into master netting agreements with its counterparties.  The master netting agreement is a standardized, bilateral contract between a given counterparty and Athlon.  Instead of treating each financial transaction between the counterparty and Athlon separately, the master netting agreement enables the counterparty and Athlon to aggregate all financial trades and treat them as a single agreement.  This arrangement is intended to benefit Athlon in two ways: (i) default by a counterparty under a single financial trade can trigger rights to terminate all financial trades with such counterparty; and (ii) netting of settlement amounts reduces Athlon’s credit exposure to a given counterparty in the event of close-out.  Athlon’s accounting policy is to not offset fair value amounts between different counterparties for derivative instruments in the accompanying Consolidated Balance Sheets.
	Tabular Disclosures of Fair Value Measurements
	The following table summarizes the fair value of Athlon’s derivative instruments not designated as hedging instruments as of the dates indicated:
		Oil			Commodity			Total
	Balance Sheet	Commodity			Derivatives			Commodity
	Location	Derivatives			Netting (a)			Derivatives
		(in thousands)
	As of September 30, 2013
	Assets
	Derivatives - current	$	162		$	(162	)	$	—
	Derivatives - noncurrent	2,149			(938		)	1,211
	Total assets	2,311			(1,100		)	1,211
	Liabilities
	Derivatives - current	(10,347		)	162			(10,185		)
	Derivatives - noncurrent	(1,930		)	938			(992		)
	Total liabilities	(12,277		)	1,100			(11,177		)
	Net liabilities	$	(9,966	)	$	—		$	(9,966	)
	As of December 31, 2012
	Assets
	Derivatives - current	$	3,386		$	(1,140	)	$	2,246
	Derivatives - noncurrent	3,265			(411		)	2,854
	Total assets	6,651			(1,551		)	5,100
	Liabilities
	Derivatives - current	(1,732		)	1,140			(592		)
	Derivatives - noncurrent	(930		)	411			(519		)
	Total liabilities	(2,662		)	1,551			(1,111		)
	Net assets	$	3,989		$	—		$	3,989
	(a)         Represents counterparty netting under master netting agreements, which allow for netting of commodity derivative contracts.  These derivative instruments are reflected net on the accompanying Consolidated Balance Sheets.
	The following table summarizes the effect of derivative instruments not designated as hedges on the accompanying Consolidated Statements of Operations for the periods indicated (in thousands):
				Amount of Loss (Gain) Recognized in Income
		Location of Loss (Gain)		Three months ended September 30,						Nine months ended September 30,
	Derivatives Not Designated as Hedges	Recognized in Income		2013			2012			2013			2012
	Commodity derivative contracts	Derivative fair value loss (gain)		$	27,037		$	14,268		$	21,331		$	(9,590	)
	Fair Value Hierarchy
	Fair value is defined as 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.  Accounting principles generally accepted in the United States (“GAAP”) establishes a three-tier fair value hierarchy, which prioritizes the inputs used to measure fair value.  The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements).  The three levels of the fair value hierarchy are defined as follows:
	·                  Level 1 — Inputs such as unadjusted, quoted prices that are available in active markets for identical assets or liabilities.
	·                  Level 2 — Inputs, other than quoted prices within Level 1, that are either directly or indirectly observable, such as quoted prices for similar assets and liabilities or quoted prices in inactive markets.
·                  Level 3 — Inputs that are unobservable for use when little or no market data exists requiring the use of valuation methodologies that result in management’s best estimate of fair value.
As required by GAAP, Athlon utilizes the most observable inputs available for the valuation technique used.  The financial assets and liabilities are classified in their entirety based on the lowest level of input that is of significance to the fair value measurement.  Athlon’s assessment of the significance of a particular input to the fair value measurement requires judgment and may affect the valuation of the financial assets and liabilities and their placement within the fair value hierarchy levels.  The following methods and assumptions were used to estimate the fair values of Athlon’s assets and liabilities that are accounted for at fair value on a recurring basis:
·                  Level 2 — Fair values of swaps are estimated using a combined income-based and market-based valuation methodology based upon forward commodity price curves obtained from independent pricing services.  Athlon’s collars are average value options.  Settlement is determined by the average underlying price over a predetermined period of time.  Athlon uses observable inputs in an option pricing valuation model to determine fair value such as: (i) current market and contractual prices for the underlying instruments; (ii) quoted forward prices for oil and natural gas; (iii) interest rates, such as a LIBOR curve for a term similar to the commodity derivative contract; and (iv) appropriate volatilities.
Athlon adjusts the valuations from the valuation model for nonperformance risk.  For commodity derivative contracts which are in an asset position, Athlon adds the counterparty’s credit default swap spread to the risk-free rate.  If a counterparty does not have a credit default swap spread, Athlon uses other companies with similar credit ratings to determine the applicable spread.  For commodity derivative contracts which are in a liability position, Athlon uses the yield on its senior notes less the risk-free rate.  All fair values have been adjusted for nonperformance risk resulting in a decrease in the net commodity derivative liability of approximately $136,000 as of September 30, 2013 and an increase in the net commodity derivative asset of approximately $125,000 as of December 31, 2012.
The following table sets forth Athlon’s assets and liabilities that were accounted for at fair value on a recurring basis as of the dates indicated:
				Fair Value Measurements at Reporting Date Using
				Quoted Prices in
				Active Markets for			Significant Other			Significant
				Identical Assets			Observable Inputs			Unobservable Inputs
Description	Asset (liability), net			(Level 1)			(Level 2)			(Level 3)
	(in thousands)
As of September 30, 2013
Oil derivative contracts - swaps	$	(9,622	)	$	—		$	(9,622	)	$	—
Oil derivative contracts - basis differential swaps	(330		)	—			(330		)	—
Oil derivative contracts - collars	(14		)	—			(14		)	—
Total	$	(9,966	)	$	—		$	(9,966	)	$	—
As of December 31, 2012
Oil derivative contracts - swaps	$	4,069		$	—		$	4,069		$	—
Oil derivative contracts - collars	(80		)	—			(80		)	—
Total	$	3,989		$	—		$	3,989		$	—

Asset_Retirement_Obligations

Asset Retirement Obligations	9 Months Ended
	Sep. 30, 2013
Asset Retirement Obligations	'
Asset Retirement Obligations	'
	Note 5. Asset Retirement Obligations
	Asset retirement obligations relate to future plugging and abandonment expenses on oil and natural gas properties and related facilities disposal.  The following table summarizes the changes in Athlon’s asset retirement obligations for the nine months ended September 30, 2013 (in thousands):
	Balance at January 1	$	5,049
	Liabilities assumed in acquisitions	335
	Liabilities incurred from new wells	735
	Liabilities settled	(108		)
	Accretion of discount	485
	Revisions of previous estimates	3
	Balance at September 30	6,499
	Less: current portion	60
	Asset retirement obligations - long-term	$	6,439

LongTerm_Debt

Long-Term Debt	9 Months Ended
	Sep. 30, 2013
Long-Term Debt	'
Long-Term Debt	'
	Note 6. Long-Term Debt
	Senior Notes
	In April 2013, Holdings issued $500 million aggregate principal amount of 7 3/8% senior notes due 2021 (the “Notes”).  The net proceeds from the Notes were used to repay a portion of the outstanding borrowings under Holdings’ credit agreement, to repay in full and terminate Holdings’ former second lien term loan, to make a $75 million distribution to Holdings’ Class A limited partners, and for general partnership purposes.  On August 14, 2013, Holdings entered into a supplemental indenture pursuant to which Athlon became an unconditional guarantor of the Notes.
	The indenture governing the Notes contains covenants, including, among other things, covenants that restrict Holdings’ ability to:
	·                  make distributions, investments, or other restricted payments if Holdings’ fixed charge coverage ratio is less than 2.0 to 1.0;
	·                  incur additional indebtedness if Holdings’ fixed charge coverage ratio would be less than 2.0 to 1.0; and
	·                  create liens, sell assets, consolidate or merge with any other person, or engage in transactions with affiliates.
	These covenants are subject to a number of important qualifications, limitations, and exceptions.  In addition, the indenture contains other customary terms, including certain events of default upon the occurrence of which the senior notes may be declared immediately due and payable.
	Under the indenture, starting on April 15, 2016, Holdings will be able to redeem some or all of the Notes at a premium that will decrease over time, plus accrued and unpaid interest to the date of redemption.  Prior to April 15, 2016, Holdings will be able, at its option, to redeem up to 35% of the aggregate principal amount of the Notes at a price of 107.375% of the principal thereof, plus accrued and unpaid interest to the date of redemption, with an amount equal to the net proceeds from certain equity offerings.  In addition, at Holdings’ option, prior to April 15, 2016, Holdings may redeem some or all of the Notes at a redemption price equal to 100% of the principal amount of the Notes, plus an “applicable premium”, plus accrued and unpaid interest to the date of redemption.  If a change of control occurs on or prior to July 15, 2014, Holdings may redeem all, but not less than all, of the notes at 110% of the principal amount thereof plus accrued and unpaid interest to, but not including, the redemption date.  Certain asset dispositions will be triggering events that may require Holdings to repurchase all or any part of a noteholder’s Notes at a purchase price in cash equal to 101% of the principal amount thereof, plus accrued and unpaid interest, if any, to but excluding the date of repurchase.  Interest on the Notes is payable in cash semi-annually in arrears, commencing on October 15, 2013, through maturity.
	As a result of the issuance of the Notes, Holdings’ former second lien term loan was paid off and retired and the borrowing base of the credit agreement was reduced resulting in a write off of unamortized debt issuance costs of approximately $2.8 million, which is included in “Interest expense” in the accompanying Consolidated Statements of Operations and “Other” in the operating activities section of the accompanying Consolidated Statements of Cash Flows for the nine months ended September 30, 2013.
	Credit Agreement
	Holdings is a party to an amended and restated credit agreement dated March 19, 2013 (the “Holdings Credit Agreement”), which matures on March 19, 2018.  The Holdings Credit Agreement provides for revolving credit loans to be made to Holdings from time to time and letters of credit to be issued from time to time for the account of Holdings or any of its restricted subsidiaries.  The aggregate amount of the commitments of the lenders under the Holdings Credit Agreement is $1.0 billion.  Availability under the Holdings Credit Agreement is subject to a borrowing base, which is redetermined semi-annually and upon requested special redeterminations.
	In conjunction with the offering of the Notes in April 2013 as discussed above, the borrowing base under the Holdings Credit Agreement was reduced to $267.5 million.  In May 2013, Holdings amended the Holdings Credit Agreement to, among other things, increase the borrowing base to $320 million.  As of September 30, 2013, the borrowing base was $320 million and there were no outstanding borrowings and no outstanding letters of credit under the Holdings Credit Agreement.  Please see "Note 12. Subsequent Events" for discussion of Athlon's borrowing base redetermination.
	Obligations under the Holdings Credit Agreement are secured by a first-priority security interest in substantially all of Holdings’ proved reserves and in the equity interests of its operating subsidiaries.  In addition, obligations under the Holdings Credit Agreement are guaranteed by Athlon and Holdings’ operating subsidiaries.
	Loans under the Holdings Credit Agreement are subject to varying rates of interest based on (i) outstanding borrowings in relation to the borrowing base and (ii) whether the loan is a Eurodollar loan or a base rate loan.  Eurodollar loans under the Holdings Credit Agreement bear interest at the Eurodollar rate plus the applicable margin indicated in the following table, and base rate loans under the Holdings Credit Agreement bear interest at the base rate plus the applicable margin indicated in the following table.  Holdings also incurs a quarterly commitment fee on the unused portion of the Holdings Credit Agreement indicated in the following table:
	Ratio of Outstanding Borrowings to Borrowing Base	Unused		Applicable		Applicable
		Commitment Fee		Margin for		Margin for Base
				Eurodollar Loans		Rate Loans
	Less than or equal to .30 to 1	0.375	%	1.5	%	0.5	%
	Greater than .30 to 1 but less than or equal to .60 to 1	0.375	%	1.75	%	0.75	%
	Greater than .60 to 1 but less than or equal to .80 to 1	0.5	%	2	%	1	%
	Greater than .80 to 1 but less than or equal to .90 to 1	0.5	%	2.25	%	1.25	%
	Greater than .90 to 1	0.5	%	2.5	%	1.5	%
	The “Eurodollar rate” for any interest period (either one, two, three, or nine months, as selected by Holdings) is the rate equal to the British Bankers Association London Interbank Offered Rate (“LIBOR”) for deposits in dollars for a similar interest period.  The “Base Rate” is calculated as the highest of: (i) the annual rate of interest announced by Bank of America, N.A. as its “prime rate”; (ii) the federal funds effective rate plus 0.5%; or (iii) except during a “LIBOR Unavailability Period”, the Eurodollar rate (for dollar deposits for a one-month term) for such day plus 1.0%.
	Any outstanding letters of credit reduce the availability under the Holdings Credit Agreement.  Borrowings under the Holdings Credit Agreement may be repaid from time to time without penalty.
	The Holdings Credit Agreement contains covenants including, among others, the following:
	·                  a prohibition against incurring debt, subject to permitted exceptions;
	·                  a restriction on creating liens on Holdings’ assets and the assets of its operating subsidiaries, subject to permitted exceptions;
	·                  restrictions on merging and selling assets outside the ordinary course of business;
	·                  restrictions on use of proceeds, investments, transactions with affiliates, or change of principal business;
	·                  a requirement that Holdings maintain a ratio of consolidated total debt to EBITDAX (as defined in the Holdings Credit Agreement) of not more than 4.75 to 1.0 (which ratio changes to 4.5 to 1.0 beginning with the quarter ending June 30, 2014); and
	·                  a provision limiting commodity derivative contracts to a volume not exceeding 85% of projected production from proved reserves for a period not exceeding 66 months from the date the commodity derivative contract is entered into.
	The Holdings Credit Agreement contains customary events of default, including our failure to comply with the financial ratios described above, which would permit the lenders to accelerate the debt if not cured within applicable grace periods.  If an event of default occurs and is continuing, lenders with a majority of the aggregate commitments may require Bank of America, N.A. to declare all amounts outstanding under the Holdings Credit Agreement to be immediately due and payable.

Stockholders_Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2013
Stockholders' Equity	'
Stockholders' Equity	'
	Note 7. Stockholders’ Equity
	In connection with Athlon’s incorporation on April 1, 2013 under the laws of the State of Delaware, it issued 1,000 shares of its common stock to Athlon Holdings GP LLC for an aggregate purchase price of $10.00.  On April 26, 2013, in connection with Athlon’s reorganization transactions, certain holders of limited partner interests in Holdings exchanged their Class A interests and Class B interests for an aggregate of 960,907 shares of Athlon’s common stock.  In connection with the effectiveness of Athlon’s IPO, these shares were subject to an adjustment based on Athlon’s IPO price of $20.00 per share and an actual 65.266-for-1 stock split resulting in 66,339,615 shares of Athlon’s common stock to be outstanding prior to the closing of the IPO.
	As discussed in “Note 1. Formation of the Company and Description of Business”, on August 7, 2013, Athlon completed its IPO of 15,789,474 shares of its common stock at $20.00 per share and received net proceeds of approximately $295.6 million, after deducting underwriting discounts and commissions and offering expenses.  Athlon used the net proceeds from the IPO to purchase New Holdings Units from Holdings.  Holdings used the proceeds it received as a result of Athlon’s purchase of New Holdings Units (i) to reduce outstanding borrowings under the Holdings Credit Agreement, (ii) to provide additional liquidity for use in its drilling program, and (iii) for general corporate purposes, including potential acquisitions.  Upon consummation of the IPO, Athlon’s ownership percentage of Holdings increased, resulting in a decrease in the noncontrolling interest from approximately 3.2% to approximately 2.2%.
	During the third quarter of 2013, Athlon recorded a reclassification of approximately $12.5 million from “Retained earnings” to “Additional paid-in capital” on the accompanying Consolidated Statement of Changes in Equity related to derivative activity that occurred prior to Athlon’s corporate reorganization on April 26, 2013.  This resulted in a decrease in “Net income attributable to noncontrolling interest” on the accompanying Consolidated Statements of Operations of approximately $0.4 million during the third quarter of 2013.

Earnings_Per_Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2013
Earnings Per Share	'
Earnings Per Share	'
	Note 8. Earnings Per Share
	Prior to the consummation of Athlon’s IPO, Athlon had 960,907 shares of outstanding common stock.  In conjunction with the closing of the IPO, certain Class A limited partners and Class B limited partners of Holdings that exchanged their interests for shares of Athlon’s common stock were subject to an adjustment based on Athlon’s IPO price of $20.00 per share and an actual 65.266-for-1 stock split.  Following this adjustment and stock split, the number of outstanding shares of Athlon’s common stock increased from 960,907 shares to 66,339,615 shares.  The one-to-one conversion of the Holdings interests in April 2013 to 960,907 shares of Athlon common stock that occurred in connection with the IPO is akin to a stock split and has been treated as such in Athlon’s earnings per share (“EPS”) calculations.  Accordingly, Athlon assumes that 66,339,615 shares of common stock were outstanding during periods prior to Athlon’s IPO for purposes of calculating EPS.
	The following table reflects the allocation of net income (loss) to common stockholders and EPS computations for the periods indicated:
		Three months ended September 30,						Nine months ended September 30,
		2013			2012			2013			2012
		(in thousands, except per share amounts)
	Basic EPS
	Numerator:
	Undistributed net income (loss) attributable to stockholders	$	2,482		$	(2,096	)	$	37,058		$	42,508
	Participation rights of unvested RSUs in undistributed earnings	(6		)	—			(6		)	—
	Basic undistributed net income (loss) attributable to stockholders	$	2,476		$	(2,096	)	$	37,052		$	42,508
	Denominator:
	Basic weighted average shares outstanding	76,637			66,340			69,810			66,340
	Basic EPS attributable to stockholders	$	0.03		$	(0.03	)	$	0.53		$	0.64
	Diluted EPS
	Numerator:
	Undistributed net income (loss) attributable to stockholders	$	2,482		$	(2,096	)	$	37,058		$	42,508
	Participation rights of unvested RSUs in undistributed earnings	(6		)	—			(6		)	—
	Effect of conversion of New Holdings Units to shares of Athlon’s common stock	(215		)	—			616			—
	Diluted undistributed net income (loss) attributable to stockholders	$	2,261		$	(2,096	)	$	37,668		$	42,508
	Denominator:
	Basic weighted average shares outstanding	76,637			66,340			69,810			66,340
	Effect of conversion of New Holdings Units to shares of Athlon’s common stock (a)	1,856			—			1,856			1,856
	Diluted weighted average shares outstanding	78,493			66,340			71,666			68,196
	Diluted EPS attributable to stockholders	$	0.03		$	(0.03	)	$	0.53		$	0.62
	(a)         For the three months ended September 30, 2012, 1,855,563 New Holdings Units were outstanding but excluded from the EPS calculations because their effect would have been antidilutive.

Incentive_Stock_Plans

Incentive Stock Plans	9 Months Ended
	Sep. 30, 2013
Incentive Stock Plans	'
Incentive Stock Plans	'
	Note 9.  Incentive Stock Plans
	In August 2013, Athlon adopted the Athlon Energy Inc. 2013 Incentive Award Plan (the “Plan”).  The principal purpose of the Plan will be to attract, retain and engage selected employees, consultants, and directors through the granting of equity and equity-based compensation awards.  Employees, consultants, and directors of Athlon and its subsidiaries are eligible to receive awards under the Plan.  The Compensation Committee will administer the Plan unless our Board of Directors assumes direct authority for administration.  The Plan provides for the grant of stock options (including non-qualified stock options and incentive stock options), restricted stock, dividend equivalents, stock payments, restricted stock units (“RSUs”), performance awards, stock appreciation rights, and other equity-based and cash-based awards, or any combination thereof.
	Initially, the aggregate number of our shares of common stock available for issuance pursuant to awards granted under the Plan will be the sum of 8,400,000 shares, subject to adjustment as described below plus an annual increase on the first day of each calendar year beginning January 1, 2014 and ending on and including the last January 1 prior to the expiration date of the Plan, equal to the least of (i) 12,000,000 shares, (ii) 4% of the shares outstanding (on an as-converted basis) on the final day of the immediately preceding calendar year, and (iii) such smaller number of shares as determined by the Board of Directors.  This number will also be adjusted due to the following shares becoming eligible to be used again for grants under the Plan:
	·                  shares subject to awards or portions of awards granted under the Plan which are forfeited, expire, or lapse for any reason, or are settled for cash without the delivery of shares, to the extent of such forfeiture, expiration, lapse or cash settlement; and
	·                  shares that Athlon repurchases prior to vesting so that such shares are returned to Athlon.
	The Plan does not provide for individual limits on awards that may be granted to any individual participant under the Plan.  Rather, the amount of awards to be granted to individual participants are determined by the Board of Directors or the Compensation Committee from time to time, as part of their compensation decision-making processes, provided, however, that the Plan does not permit awards having a grant date fair value in excess of $700,000 to be granted to Athlon’s non-employee directors in any year.
	As of September 30, 2013, there were 7,776,087 shares available for issuance under the Plan.  During the nine months ended September 30, 2013, Athlon recorded non-cash stock-based compensation expense related to the Plan of $492,000, which was allocated to lease operating expense and general and administrative expense in the accompanying Consolidated Statements of Operations based on the allocation of the respective employees’ compensation.  During the nine months ended September 30, 2013, Athlon capitalized $37,000 of non-cash stock-based compensation expense related to the Plan as a component of “Proved properties, including wells and related equipment” in the accompanying Consolidated Balance Sheets.
	RSUs vest over three years, subject to performance criteria for certain members of management.  The following table summarizes the changes in Athlon’s unvested RSUs for the nine months ended September 30, 2013:
			Weighted -
			Average
		Number of	Grant Date
		Shares	Fair Value
	Outstanding at January 1	—	$	—
	Granted	623,913	32.21
	Vested	—	—
	Forfeited	—	—
	Outstanding at September 30	623,913	32.21
	As of September 30, 2013, there were 396,413 unvested RSUs, all of which were granted during September 2013, in which the vesting is dependent only on the passage of time and continued employment.  Additionally, as of September 30, 2013, there were 227,500 unvested RSUs, all of which were granted during September 2013, in which the vesting is dependent not only on the passage of time and continued employment, but also on the achievement of certain performance criteria.
	None of Athlon’s unvested RSUs are subject to variable accounting.  As of September 30, 2013, Athlon had approximately $17.9 million of total unrecognized compensation cost related to unvested RSUs, which is expected to be recognized over a weighted-average period of approximately 2.8 years.
	Class B Interests
	Holdings’ limited partnership agreement provided for the issuance of Class B limited partner interests.  As discussed in “Note 1. Formation of the Company and Description of Business”, in connection with Holdings’ corporate reorganization, the holders of the Class B limited partner interests in Holdings exchanged their interests for common stock of Athlon subject to the same conditions and vesting terms.  Upon the consummation of Athlon’s IPO on August 1, 2013, the remaining unvested common stock awards, which were formerly Class B interests in Holdings, vested and Athlon recognized non-cash equity-based compensation expense of approximately $1.5 million.
	During the nine months ended September 30, 2013 and 2012, Athlon recorded approximately $1.3 million and $186,000, respectively, of non-cash equity-based compensation expense related to Class B interests, which was allocated to lease operating expense and general and administrative expenses in the accompanying Consolidated Statements of Operations based on the allocation of the respective employees’ compensation.  During the nine months ended September 30, 2013 and 2012, Athlon capitalized approximately $421,000 and $68,000, respectively, of non-cash stock-based compensation expense related to Class B interests as a component of “Proved properties, including wells and related equipment” in the accompanying Consolidated Balance Sheets.

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies	'
Commitments and Contingencies	'
	Note 10. Commitments and Contingencies
	From time to time, Athlon is a party to ongoing legal proceedings in the ordinary course of business, including workers’ compensation claims and employment related disputes.  Management does not believe the results of these proceedings, individually or in the aggregate, will have a material adverse effect on Athlon’s business, financial position, results of operations, or liquidity.
	Additionally, Athlon has contractual obligations related to future plugging and abandonment expenses on oil and natural gas properties and related facilities disposal, long-term debt, commodity derivative contracts, operating leases, and development commitments.

Related_Party_Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2013
Related Party Transactions	'
Related Party Transactions	'
	Note 11. Related Party Transactions
	Transaction Fee Agreement
	Holdings was a party to a Transaction Fee Agreement, dated August 23, 2010, which required Holdings to pay a fee to Apollo equal to 2% of the total equity contributed to Holdings, as defined in the agreement, in exchange for consulting and advisory services provided by Apollo.  In October 2012, Apollo assigned its rights and obligations under the Transaction Fee Agreement to an affiliate, Apollo Global Securities, LLC.  Upon the consummation of Athlon’s IPO, Holdings terminated the Transaction Fee Agreement.  Since Holdings’ inception through the termination of the Transaction Fee Agreement, it incurred transaction fees under the Transaction Fee Agreement of approximately $7.5 million in total.
	Services Agreement
	Holdings was a party to a Services Agreement, dated August 23, 2010, which required Holdings to compensate Apollo for consulting and advisory services equal to the higher of (i) 1% of earnings before interest, income taxes, DD&A, and exploration expense per quarter and (ii) $62,500 per quarter (the “Advisory Fee”); provided, however, that such Advisory Fee for any calendar year shall not exceed $500,000.  The Services Agreement also provided for reimbursement to Apollo for any reasonable out-of-pocket expenses incurred while performing services under the Services Agreement.  During the nine months ended September 30, 2013 and 2012, Holdings incurred approximately $500,000 and $493,000, respectively, of Advisory Fees.  All fees incurred under the Services Agreement are included in “General and administrative expenses” in the accompanying Consolidated Statements of Operations.
	Upon the consummation of Athlon’s IPO, Holdings terminated the Services Agreement and, in connection with the termination, Holdings paid $2.4 million (plus $132,000 of unreimbursed fees) to Apollo.  Such payment corresponded to the present value as of the date of termination of the aggregate annual fees that would have been payable during the remainder of the term of the Services Agreement (assuming a term ending on August 23, 2020).  Under the Services Agreement, Holdings also agreed to indemnify Apollo and its affiliates and their respective limited partners, general partners, directors, members, officers, managers, employees, agents, advisors, their directors, officers, and representatives for potential losses relating to the services contemplated under the Services Agreement.
	Participation of Apollo Global Securities, LLC in Senior Notes Offering and IPO
	Apollo Global Securities, LLC is an affiliate of the Apollo Funds and received a portion of the gross spread as an initial purchaser of the Notes of $0.5 million.  Apollo Global Securities, LLC was also an underwriter in Athlon’s IPO and received a portion of the discounts and commissions paid to the underwriters in the IPO of approximately $0.9 million.
	Distribution
	Holdings used a portion of the net proceeds from the Notes to make a distribution to its Class A limited partners, including the Apollo Funds and its management team and employees.  The Apollo Funds received approximately $73 million of the distribution and the remaining Class A limited partners received approximately $2 million, in the aggregate.
	Exchange Agreement
	Upon the consummation of its IPO, Athlon entered into an exchange agreement with certain members of its management team and employees who hold New Holdings Units after the closing of the IPO.  Under the exchange agreement, each such holder (and certain permitted transferees thereof) may, under certain circumstances after the date of the closing of the IPO (subject to the terms of the exchange agreement), exchange their New Holdings Units for shares of Athlon’s common stock on a one-for-one basis, subject to customary conversion rate adjustments for stock splits, stock dividends, and reclassifications.  As a holder exchanges its New Holdings Units, Athlon’s interest in Holdings will be correspondingly increased.
	Tax Receivable Agreement
	Upon the consummation of its IPO, Athlon entered into a tax receivable agreement with certain members of its management team and employees who hold New Holdings Units after the closing of the IPO that provides for the payment from time to time by Athlon to such unitholders of Holdings of 85% of the amount of the benefits, if any, that Athlon is deemed to realize as a result of increases in tax basis and certain other tax benefits related to exchanges of New Holdings Units pursuant to the exchange agreement, including tax benefits attributable to payments under the tax receivable agreement.  These payment obligations are obligations of Athlon and not of Holdings.  For purposes of the tax receivable agreement, the benefit deemed realized by Athlon will be computed by comparing its actual income tax liability (calculated with certain assumptions) to the amount of such taxes that Athlon would have been required to pay had there been no increase to the tax basis of the assets of Holdings as a result of the exchanges and had Athlon not entered into the tax receivable agreement.
	The step-up in basis will depend on the fair value of the New Holdings Units at conversion.  There is no intent of the holders of New Holdings Units to exchange their units for shares of Athlon’s common stock in the foreseeable future.  In addition, Athlon does not expect to be in a tax paying position before 2019.  Therefore, Athlon cannot presently estimate what the benefit or payments under the tax receivable agreement will be on a factually supportable basis, and accordingly not recognized as a liability.

Subsequent_Events

Subsequent Events	9 Months Ended
	Sep. 30, 2013
Subsequent Events	'
Subsequent Events	'
	Note 12. Subsequent Events
	In November 2013, Holdings amended the Holdings Credit Agreement to, among other things, increase the borrowing base to $525 million.  As of November 14, 2013, there were no of outstanding borrowings under the Holdings Credit Agreement.

Basis_of_Presentation_Policies

Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2013
Basis of Presentation	'
Consolidation	'
	Athlon’s consolidated financial statements include the accounts of its wholly owned and majority-owned subsidiaries.  All material intercompany balances and transactions have been eliminated in consolidation.
	In the opinion of management, the accompanying unaudited consolidated financial statements include all adjustments necessary to present fairly, in all material respects, Athlon’s financial position as of September 30, 2013, results of operations for the three and nine months ended September 30, 2013 and 2012, and cash flows for the nine months ended September 30, 2013 and 2012.  All adjustments are of a normal recurring nature.  These interim results are not necessarily indicative of results for an entire year.
	Certain amounts and disclosures have been condensed and omitted from the unaudited consolidated financial statements pursuant to the rules and regulations of the United States Securities and Exchange Commission (the “SEC”).  Therefore, these unaudited consolidated financial statements should be read in conjunction with Holdings’ audited consolidated financial statements and related notes thereto included in Athlon’s final prospectus dated August 1, 2013 and filed with the SEC pursuant to Rule 424(b)(4) of the Securities Act of 1933, as amended, on August 5, 2013.
Income Taxes	'
	Income Taxes
	Athlon accounts for income taxes using the asset and liability method.  Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards.  Deferred tax assets and liabilities are measured using enacted tax laws and rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled.  The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date.
	Athlon periodically assesses whether it is more likely than not that it will generate sufficient taxable income to realize its deferred income tax assets, including net operating losses.  In making this determination, Athlon considers all available positive and negative evidence and makes certain assumptions.  Athlon considers, among other things, its deferred tax liabilities, the overall business environment, its historical earnings and losses, current industry trends, and its outlook for future years.  Athlon believes it is more likely than not that certain net operating losses can be carried forward and utilized.
	In April 2013, Athlon had a corporate reorganization to effectuate its IPO.  Holdings, Athlon’s accounting predecessor, is a partnership not subject to federal income tax.  Pursuant to the steps of the corporate reorganization, certain Class A limited partners and the Class B limited partners of Holdings exchanged their interests for shares of Athlon’s common stock.  Athlon’s operations are now subject to federal income tax.  The tax implications of the corporate reorganization and the tax impact of the conversion to operating as a taxable entity have been reflected in the accompanying consolidated financial statements.
Noncontrolling Interest	'
	Noncontrolling Interest
	As of September 30, 2013, management and employees owned approximately 2.2% of Holdings.  Athlon owns 100% of Athlon Holdings GP LLC, which is Holdings’ general partner.  Considering the presumption of control, Athlon has fully consolidated the financial position, results of operations, and cash flows of Holdings.
	As presented in the accompanying Consolidated Balance Sheets, “Noncontrolling interest” as of September 30, 2013 of approximately $10.0 million represents management and employees’ 1,855,563 New Holdings Units that are exchangeable for shares of Athlon’s common stock on a one-for-one basis.  As presented in the accompanying Consolidated Statements of Operations, “Net income (loss) attributable to noncontrolling interest” for the three and nine months ended September 30, 2013 of approximately $(0.2) million and $0.6 million, respectively, represents the net income of Holdings attributable to management and employees since April 26, 2013.
	The following table summarizes the effects of changes in Athlon’s partnership interest in Holdings on Athlon’s equity for the periods indicated:
		Three		Nine months
		months		ended
		ended		September
		September		30, 2013
		30, 2013
		(in thousands)
	Net income attributable to stockholders	$	2,482	$	37,058
	Transfer from noncontrolling interest:
	Increase in Athlon’s paid-in capital for corporate reorganization	—		290,950
	Increase in Athlon’s paid-in capital for issuance of 15,789,474 shares of common stock in initial public offering	295,473		295,473
	Net transfer from noncontrolling interest	295,473		586,423
	Change from net income attributable to stockholders and transfers from (to) noncontrolling interest	$	297,955	$	623,481
New Accounting Pronouncements	'
	New Accounting Pronouncements
	In December 2011, the Financial Accounting Standards Board issued Accounting Standards Update (“ASU”) 2011-11, “Disclosures about Offsetting Assets and Liabilities” and in January 2013 issued ASU 2013-01, “Clarifying the Scope of Disclosures About Offsetting Assets and Liabilities”.  These ASUs created new disclosure requirements regarding the nature of an entity’s rights of setoff and related arrangements associated with its derivative instruments, repurchase agreements, and securities lending transactions.  Certain disclosures of the amounts of certain instruments subject to enforceable master netting arrangements are required, irrespective of whether the entity has elected to offset those instruments in the statement of financial position.  These ASUs were effective retrospectively for annual reporting periods beginning on or after January 1, 2013.  The adoption of these ASUs did not impact Athlon’s financial position, results of operations, or liquidity.
	No other new accounting pronouncements issued or effective from January 1, 2013 through the date of this Report, had or are expected to have a material impact on Athlon’s unaudited consolidated financial statements.

Basis_of_Presentation_Tables

Basis of Presentation (Tables)	9 Months Ended
	Sep. 30, 2013
Basis of Presentation	'
Summary of effects of changes in Athlon's partnership interest in Holdings on Athlon's equity	'
		Three		Nine months
		months		ended
		ended		September
		September		30, 2013
		30, 2013
		(in thousands)
	Net income attributable to stockholders	$	2,482	$	37,058
	Transfer from noncontrolling interest:
	Increase in Athlon’s paid-in capital for corporate reorganization	—		290,950
	Increase in Athlon’s paid-in capital for issuance of 15,789,474 shares of common stock in initial public offering	295,473		295,473
	Net transfer from noncontrolling interest	295,473		586,423
	Change from net income attributable to stockholders and transfers from (to) noncontrolling interest	$	297,955	$	623,481

Proved_Properties_Tables

Proved Properties (Tables)	9 Months Ended
	Sep. 30, 2013
Proved Properties	'
Schedule of proved properties including wells and related equipment	'
		September 30,		December 31,
		2013		2012
		(in thousands)
	Proved leasehold costs	$	411,657	$	376,271
	Wells and related equipment - Completed	634,980		379,036
	Wells and related equipment - In process	38,244		33,264
	Total proved properties	$	1,084,881	$	788,571

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2013
Fair Value Measurements	'
Summary of open commodity derivative contracts	'
		Average		Weighted -			Average		Weighted -			Average		Weighted -		Asset
		Daily		Average			Daily		Average			Daily		Average		(Liability)
		Floor		Floor			Cap		Cap			Swap		Swap		Fair Market
	Period	Volume		Price			Volume		Price			Volume		Price		Value
		(Bbl)		(per Bbl)			(Bbl)		(per Bbl)			(Bbl)		(per Bbl)		(in thousands)
	Oct. - Dec. 2013	150		$	75		150		$	105.95		7,000		$	95.01	$	(4,205	)
	2014	—		—			—		—			7,950		92.67		(7,532		)
	2015	—		—			—		—			1,300		93.18		2,101
																$	(9,636	)
Schedule of committed 10% or greater (in terms of fair market value) of oil derivative contracts in asset positions from counterparties, or their affiliates	'
		Fair Market Value of
		Oil Derivative
		Contracts
	Counterparty	Committed
		(in thousands)
	BNP Paribas	$	458
Schedule of fair value of derivative instruments not designated as hedging instruments	'
		Oil			Commodity			Total
	Balance Sheet	Commodity			Derivatives			Commodity
	Location	Derivatives			Netting (a)			Derivatives
		(in thousands)
	As of September 30, 2013
	Assets
	Derivatives - current	$	162		$	(162	)	$	—
	Derivatives - noncurrent	2,149			(938		)	1,211
	Total assets	2,311			(1,100		)	1,211
	Liabilities
	Derivatives - current	(10,347		)	162			(10,185		)
	Derivatives - noncurrent	(1,930		)	938			(992		)
	Total liabilities	(12,277		)	1,100			(11,177		)
	Net liabilities	$	(9,966	)	$	—		$	(9,966	)
	As of December 31, 2012
	Assets
	Derivatives - current	$	3,386		$	(1,140	)	$	2,246
	Derivatives - noncurrent	3,265			(411		)	2,854
	Total assets	6,651			(1,551		)	5,100
	Liabilities
	Derivatives - current	(1,732		)	1,140			(592		)
	Derivatives - noncurrent	(930		)	411			(519		)
	Total liabilities	(2,662		)	1,551			(1,111		)
	Net assets	$	3,989		$	—		$	3,989
	(a)         Represents counterparty netting under master netting agreements, which allow for netting of commodity derivative contracts.  These derivative instruments are reflected net on the accompanying Consolidated Balance Sheets.
Schedule of effect of derivative instruments not designated as hedges on accompanying consolidated statements of operation	'
	The following table summarizes the effect of derivative instruments not designated as hedges on the accompanying Consolidated Statements of Operations for the periods indicated (in thousands):
				Amount of Loss (Gain) Recognized in Income
		Location of Loss (Gain)		Three months ended September 30,						Nine months ended September 30,
	Derivatives Not Designated as Hedges	Recognized in Income		2013			2012			2013			2012
	Commodity derivative contracts	Derivative fair value loss (gain)		$	27,037		$	14,268		$	21,331		$	(9,590	)
Schedule of assets and liabilities that accounted for at fair value on a recurring basis	'
					Fair Value Measurements at Reporting Date Using
					Quoted Prices in
					Active Markets for			Significant Other			Significant
					Identical Assets			Observable Inputs			Unobservable Inputs
	Description	Asset (liability), net			(Level 1)			(Level 2)			(Level 3)
		(in thousands)
	As of September 30, 2013
	Oil derivative contracts - swaps	$	(9,622	)	$	—		$	(9,622	)	$	—
	Oil derivative contracts - basis differential swaps	(330		)	—			(330		)	—
	Oil derivative contracts - collars	(14		)	—			(14		)	—
	Total	$	(9,966	)	$	—		$	(9,966	)	$	—
	As of December 31, 2012
	Oil derivative contracts - swaps	$	4,069		$	—		$	4,069		$	—
	Oil derivative contracts - collars	(80		)	—			(80		)	—
	Total	$	3,989		$	—		$	3,989		$	—

Asset_Retirement_Obligations_T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 2013
Asset Retirement Obligations	'
Summary of changes in asset retirement obligations	'
	The following table summarizes the changes in Athlon’s asset retirement obligations for the nine months ended September 30, 2013 (in thousands):
	Balance at January 1	$	5,049
	Liabilities assumed in acquisitions	335
	Liabilities incurred from new wells	735
	Liabilities settled	(108		)
	Accretion of discount	485
	Revisions of previous estimates	3
	Balance at September 30	6,499
	Less: current portion	60
	Asset retirement obligations - long-term	$	6,439

LongTerm_Debt_Tables

Long-Term Debt (Tables)	9 Months Ended
	Sep. 30, 2013
Long-Term Debt	'
Schedule of quarterly commitment fee on unused portion of the Holdings Credit Agreement and applicable margin for Eurodollar and base rate loans	'
	Ratio of Outstanding Borrowings to Borrowing Base	Unused		Applicable		Applicable
		Commitment Fee		Margin for		Margin for Base
				Eurodollar Loans		Rate Loans
	Less than or equal to .30 to 1	0.375	%	1.5	%	0.5	%
	Greater than .30 to 1 but less than or equal to .60 to 1	0.375	%	1.75	%	0.75	%
	Greater than .60 to 1 but less than or equal to .80 to 1	0.5	%	2	%	1	%
	Greater than .80 to 1 but less than or equal to .90 to 1	0.5	%	2.25	%	1.25	%
	Greater than .90 to 1	0.5	%	2.5	%	1.5	%

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2013
Earnings Per Share	'
Schedule of allocation of net income (loss) to common stockholders and earnings per share (EPS) computations	'
		Three months ended September 30,						Nine months ended September 30,
		2013			2012			2013			2012
		(in thousands, except per share amounts)
	Basic EPS
	Numerator:
	Undistributed net income (loss) attributable to stockholders	$	2,482		$	(2,096	)	$	37,058		$	42,508
	Participation rights of unvested RSUs in undistributed earnings	(6		)	—			(6		)	—
	Basic undistributed net income (loss) attributable to stockholders	$	2,476		$	(2,096	)	$	37,052		$	42,508
	Denominator:
	Basic weighted average shares outstanding	76,637			66,340			69,810			66,340
	Basic EPS attributable to stockholders	$	0.03		$	(0.03	)	$	0.53		$	0.64
	Diluted EPS
	Numerator:
	Undistributed net income (loss) attributable to stockholders	$	2,482		$	(2,096	)	$	37,058		$	42,508
	Participation rights of unvested RSUs in undistributed earnings	(6		)	—			(6		)	—
	Effect of conversion of New Holdings Units to shares of Athlon’s common stock	(215		)	—			616			—
	Diluted undistributed net income (loss) attributable to stockholders	$	2,261		$	(2,096	)	$	37,668		$	42,508
	Denominator:
	Basic weighted average shares outstanding	76,637			66,340			69,810			66,340
	Effect of conversion of New Holdings Units to shares of Athlon’s common stock (a)	1,856			—			1,856			1,856
	Diluted weighted average shares outstanding	78,493			66,340			71,666			68,196
	Diluted EPS attributable to stockholders	$	0.03		$	(0.03	)	$	0.53		$	0.62
	(a)         For the three months ended September 30, 2012, 1,855,563 New Holdings Units were outstanding but excluded from the EPS calculations because their effect would have been antidilutive.

Incentive_Stock_Plans_Tables

Incentive Stock Plans (Tables)	9 Months Ended
	Sep. 30, 2013
Incentive Stock Plans	'
Summary of changes in unvested RSUs	'
			Weighted -
			Average
		Number of	Grant Date
		Shares	Fair Value
	Outstanding at January 1	—	$	—
	Granted	623,913	32.21
	Vested	—	—
	Forfeited	—	—
	Outstanding at September 30	623,913	32.21

Formation_of_the_Company_and_D1

Formation of the Company and Description of Business (Details) (USD $)	0 Months Ended	9 Months Ended
	Aug. 07, 2013	Sep. 30, 2013	Apr. 26, 2013
Formation of the Company and Description of Business	'	'	'
Tax impact of corporate reorganization	'	'	$73,200,000
Initial public offering	'	'	'
Shares of common stock issued in IPO	15,789,474	'	'
Per share price (in dollars per share)	$20	'	'
Net proceeds from IPO, after deducting underwriting discounts and commissions and offering expenses (in dollars)	$295,600,000	$296,044,000	'
Holdings	'	'	'
Initial public offering	'	'	'
Number of common stock exchangeable against each unit	'	1	'
Holdings | Class A limited partners	'	'	'
Initial public offering	'	'	'
Exchange Agreement Number of New Units Exchangeable Against Limited Partner Interest	1,855,563	'	'

Basis_of_Presentation_Details

Basis of Presentation (Details) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Aug. 07, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Noncontrolling interest	'	'	'	'	'
Noncontrolling interest	'	$10,045	'	$10,045	'
Net income (loss) attributable to noncontrolling interest	'	-215	'	616	'
Effects of changes in Athlon's partnership interest in Holdings on Athlon's equity	'	'	'	'	'
Net income attributable to stockholders	'	2,476	-2,096	37,052	42,508
Transfer from noncontrolling interest:	'	'	'	'	'
Shares of common stock in public offering	15,789,474	'	'	'	'
Athlon Holdings GP LLC	'	'	'	'	'
Noncontrolling interest	'	'	'	'	'
Ownership interest in general partner of Holdings	'	100.00%	'	100.00%	'
Holdings	'	'	'	'	'
Noncontrolling interest	'	'	'	'	'
Percentage of ownership interest of management and employees	3.20%	2.20%	'	2.20%	'
Number of common stock exchangeable against each unit	'	'	'	1	'
Holdings | Athlon Holdings GP LLC	'	'	'	'	'
Effects of changes in Athlon's partnership interest in Holdings on Athlon's equity	'	'	'	'	'
Net income attributable to stockholders	'	2,482	'	37,058	'
Transfer from noncontrolling interest:	'	'	'	'	'
Increase in Athlon's paid-in capital for corporate reorganization	'	'	'	290,950	'
Increase in Athlon's paid-in capital for issuance of 15,789,474 shares of common stock in initial public offering	'	295,473	'	295,473	'
Shares of common stock in public offering	'	'	'	15,789,474	'
Net transfer from noncontrolling interest	'	295,473	'	586,423	'
Change from net income attributable to stockholders and transfers from (to) noncontrolling interest	'	$297,955	'	$623,481	'
Holdings | Class A limited partners	'	'	'	'	'
Noncontrolling interest	'	'	'	'	'
Exchange Agreement Number of New Units Exchangeable Against Limited Partner Interest	1,855,563	'	'	'	'

Proved_Properties_Details

Proved Properties (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Proved Properties	'	'
Proved leasehold costs	$411,657	$376,271
Wells and related equipment - Completed	634,980	379,036
Wells and related equipment - In process	38,244	33,264
Total proved properties	$1,084,881	$788,571

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (Level 1 input, USD $)	Sep. 30, 2013
In Millions, unless otherwise specified
Level 1 input	'
Fair value measurements	'
Senior notes	$515.60

Fair_Value_Measurements_Detail1

Fair Value Measurements (Details 2) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Open commodity derivative contracts	'	'
Summary of open commodity derivative contracts	'	'
Asset (Liability) Fair Market Value	$9,636	$3,989
Open commodity derivative contracts | Oct. - Dec. 2013	'	'
Summary of open commodity derivative contracts	'	'
Asset (Liability) Fair Market Value	-4,205	'
Open commodity derivative contracts | 2014	'	'
Summary of open commodity derivative contracts	'	'
Asset (Liability) Fair Market Value	-7,532	'
Open commodity derivative contracts | 2015	'	'
Summary of open commodity derivative contracts	'	'
Asset (Liability) Fair Market Value	2,101	'
Commodity derivative contracts with floor price | Oct. - Dec. 2013	'	'
Summary of open commodity derivative contracts	'	'
Average Daily Volume	150	'
Weighted-Average Floor Price	75	'
Commodity derivative contracts with cap price | Oct. - Dec. 2013	'	'
Summary of open commodity derivative contracts	'	'
Average Daily Volume	150	'
Weighted-Average Cap Price	105.95	'
Commodity derivative contracts with swap price | Oct. - Dec. 2013	'	'
Summary of open commodity derivative contracts	'	'
Average Daily Volume	7,000	'
Weighted-Average Swap Price	95.01	'
Commodity derivative contracts with swap price | 2014	'	'
Summary of open commodity derivative contracts	'	'
Average Daily Volume	7,950	'
Weighted-Average Swap Price	92.67	'
Commodity derivative contracts with swap price | 2015	'	'
Summary of open commodity derivative contracts	'	'
Average Daily Volume	1,300	'
Weighted-Average Swap Price	93.18	'
Midland-Cushing basis differential swaps | Oct. - Dec. 2013	'	'
Summary of open commodity derivative contracts	'	'
Fair value of derivative liability	$300	'
Midland-Cushing basis differential swaps | Fourth quarter of 2013	'	'
Summary of open commodity derivative contracts	'	'
Average Daily Volume	5,000	'
Weighted-Average Swap Price	1.2	'

Fair_Value_Measurements_Detail2

Fair Value Measurements (Details 3) (Master netting agreements, BNP Paribas, USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified
Master netting agreements | BNP Paribas	'
Counterparty risk	'
Fair Market Value of Oil Derivative Contracts Committed	$458

Fair_Value_Measurements_Detail3

Fair Value Measurements (Details 4) (Commodity contracts, USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Liabilities	'	'
Net assets (liabilities)	$9,636	$3,989
Derivative instruments not designated as hedging instruments | Oil	'	'
Assets	'	'
Oil Commodity Derivatives, assets	2,311	6,651
Commodity Derivatives Netting, assets	-1,100	-1,551
Total Commodity Derivatives	1,211	5,100
Liabilities	'	'
Oil Commodity Derivatives, liabilities	-12,277	-2,662
Commodity Derivatives Netting, liabilities	1,100	1,551
Total Commodity Derivatives	-11,177	-1,111
Net assets (liabilities)	-9,966	3,989
Derivative instruments not designated as hedging instruments | Oil | Derivative assets - current	'	'
Assets	'	'
Oil Commodity Derivatives, assets	162	3,386
Commodity Derivatives Netting, assets	-162	-1,140
Total Commodity Derivatives	'	2,246
Derivative instruments not designated as hedging instruments | Oil | Derivative assets - noncurrent	'	'
Assets	'	'
Oil Commodity Derivatives, assets	2,149	3,265
Commodity Derivatives Netting, assets	-938	-411
Total Commodity Derivatives	1,211	2,854
Derivative instruments not designated as hedging instruments | Oil | Derivative liabilities - current	'	'
Liabilities	'	'
Oil Commodity Derivatives, liabilities	-10,347	-1,732
Commodity Derivatives Netting, liabilities	162	1,140
Total Commodity Derivatives	-10,185	-592
Derivative instruments not designated as hedging instruments | Oil | Derivative liabilities - noncurrent	'	'
Liabilities	'	'
Oil Commodity Derivatives, liabilities	-1,930	-930
Commodity Derivatives Netting, liabilities	938	411
Total Commodity Derivatives	($992)	($519)

Fair_Value_Measurements_Detail4

Fair Value Measurements (Details 5) (Derivative instruments not designated as hedges, Commodity contracts, Derivative fair value loss (gain), USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative instruments not designated as hedges | Commodity contracts | Derivative fair value loss (gain)	'	'	'	'
Fair value measurements	'	'	'	'
Amount of Loss (Gain) Recognized in Income	$27,037	$14,268	$21,331	($9,590)

Fair_Value_Measurements_Detail5

Fair Value Measurements (Details 6) (Commodity contracts, USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Fair Value Hierarchy	'	'
Increase (decrease) in net commodity derivative asset	$136,000	$125,000
Recurring | Asset (Liability), net | Oil	'	'
Fair Value Hierarchy	'	'
Total	-9,966,000	3,989,000
Recurring | Asset (Liability), net | Oil | Swaps	'	'
Fair Value Hierarchy	'	'
Total	-9,622,000	4,069,000
Recurring | Asset (Liability), net | Oil | Basis differential swaps	'	'
Fair Value Hierarchy	'	'
Total	-330,000	'
Recurring | Asset (Liability), net | Oil | Collars	'	'
Fair Value Hierarchy	'	'
Total	-14,000	-80,000
Recurring | Significant Other Observable Inputs (Level 2) | Oil	'	'
Fair Value Hierarchy	'	'
Total	-9,966,000	3,989,000
Recurring | Significant Other Observable Inputs (Level 2) | Oil | Swaps	'	'
Fair Value Hierarchy	'	'
Total	-9,622,000	4,069,000
Recurring | Significant Other Observable Inputs (Level 2) | Oil | Basis differential swaps	'	'
Fair Value Hierarchy	'	'
Total	-330,000	'
Recurring | Significant Other Observable Inputs (Level 2) | Oil | Collars	'	'
Fair Value Hierarchy	'	'
Total	($14,000)	($80,000)

Asset_Retirement_Obligations_D

Asset Retirement Obligations (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Asset retirement obligations	'	'	'	'	'
Balance at the beginning of the period	'	'	$5,049	'	'
Liabilities incurred from new wells	'	'	735	'	'
Liabilities assumed in acquisitions	'	'	335	'	'
Liabilities settled	'	'	-108	'	'
Accretion of discount	174	123	485	343	'
Revisions of previous estimates	'	'	3	'	'
Balance at the end of the period	6,499	'	6,499	'	'
Less: current portion	60	'	60	'	'
Asset retirement obligations - long-term	$6,439	'	$6,439	'	$5,049

LongTerm_Debt_Details

Long-Term Debt (Details) (USD $)

9 Months Ended

1 Months Ended

9 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

9 Months Ended

Sep. 30, 2013

Apr. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

31-May-13

Apr. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

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Sep. 30, 2013

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Sep. 30, 2013

Sep. 30, 2013

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Sep. 30, 2013

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Sep. 30, 2013

Holdings

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Senior notes

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Former second lien term loan

Upon assets disposition triggering events

Prior to April 15, 2016

Prior to April 15, 2016

On or prior to July 15, 2014

Maximum

Maximum

Applicable Margin for Eurodollar Loans

Applicable Margin for Eurodollar Loans

Applicable Margin for Base Rate Loans

Applicable Margin for Base Rate Loans

Applicable Margin for Base Rate Loans

Applicable Margin for Base Rate Loans

Applicable Margin for Base Rate Loans

Less than or equal to .30 to 1

Less than or equal to .30 to 1

Less than or equal to .30 to 1

Greater than .30 to 1 but less than or equal to .60 to 1

Greater than .30 to 1 but less than or equal to .60 to 1

Greater than .30 to 1 but less than or equal to .60 to 1

Greater than .60 to 1 but less than or equal to .80 to 1

Greater than .60 to 1 but less than or equal to .80 to 1

Greater than .60 to 1 but less than or equal to .80 to 1

Greater than .80 to 1 but less than or equal to .90 to 1

Greater than .80 to 1 but less than or equal to .90 to 1

Greater than .80 to 1 but less than or equal to .90 to 1

Greater than .90 to 1

Greater than .90 to 1

Greater than .90 to 1

Maximum

Maximum

Maximum

Maximum

Maximum

Minimum

Minimum

Minimum

Redemption from proceeds of certain equity offerings

Redemption of debt instrument upon change of control

Prior to April 15, 2016

Eurodollar rate

LIBOR

Eurodollar rate

LIBOR

Base Rate

Prime rate

Federal funds rate

Applicable Margin for Eurodollar Loans

Applicable Margin for Base Rate Loans

Applicable Margin for Eurodollar Loans

Applicable Margin for Base Rate Loans

Applicable Margin for Eurodollar Loans

Applicable Margin for Base Rate Loans

Applicable Margin for Eurodollar Loans

Applicable Margin for Base Rate Loans

Applicable Margin for Eurodollar Loans

Applicable Margin for Base Rate Loans

Less than or equal to .30 to 1

Greater than .30 to 1 but less than or equal to .60 to 1

Greater than .60 to 1 but less than or equal to .80 to 1

Greater than .80 to 1 but less than or equal to .90 to 1

Greater than .90 to 1

Greater than .30 to 1 but less than or equal to .60 to 1

Greater than .60 to 1 but less than or equal to .80 to 1

Greater than .80 to 1 but less than or equal to .90 to 1

Redemption from proceeds of certain equity offerings

Long-term debt

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate principal amount of notes issued

'

$500,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate (as a percent)

'

7.38%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Distribution paid to Class A limited partners

75,000,000

75,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fixed charge coverage ratio

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of aggregate principal amount of notes that can be redeemed

'

'

'

'

'

'

'

35.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Redemption price of debt instrument (as a percent)

'

'

101.00%

100.00%

107.38%

110.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Write off of unamortized debt issuance costs

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2,800,000

Maximum amount committed by lender

'

'

'

'

'

'

'

'

1,000,000,000

1,000,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Current borrowing base

'

'

'

'

'

'

'

'

320,000,000

320,000,000

320,000,000

267,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding borrowings

'

'

'

'

'

'

'

'

0

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding letters of credit

'

'

'

'

'

'

'

'

$0

$0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ratio of Outstanding Borrowings to Borrowing Base

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.3

0.6

0.8

0.9

0.9

0.3

0.6

0.8

'

Unused Commitment Fee (as a percent)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.38%

'

'

0.38%

'

'

0.50%

'

'

0.50%

'

'

0.50%

'

'

'

'

'

'

'

'

'

'

'

Applicable Margin (as a percent)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.00%

'

'

'

0.50%

'

1.50%

0.50%

'

1.75%

0.75%

'

2.00%

1.00%

'

2.25%

1.25%

'

2.50%

1.50%

'

'

'

'

'

'

'

'

'

Variable interest rate base

'

'

'

'

'

'

'

'

'

'

'

'

'Eurodollar rate

'LIBOR

'Eurodollar rate

'LIBOR

'Base Rate

'prime rate

'Federal fund

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ratio of consolidated total debt to EBITDAX beginning with quarter ended June 30, 2013

'

'

'

'

'

'

'

'

4.75

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ratio of consolidated total debt to EBITDAX beginning with quarter ended June 30, 2014

'

'

'

'

'

'

'

'

'

4.5

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Maximum projected production that can be hedged (as a percent)

'

'

'

'

'

'

'

'

'

85.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Period over which hedging limitation requirement of the projected production from proved reserve is required to be maintained

'

'

'

'

'

'

'

'

'

'66 months

'

'

'

'

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'

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'

'

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'

Stockholders_Equity_Details

Stockholders' Equity (Details) (USD $)	0 Months Ended			3 Months Ended	9 Months Ended
	Aug. 07, 2013	Apr. 26, 2013	Apr. 02, 2013	Sep. 30, 2013	Sep. 30, 2013
Stockholders' Equity	'	'	'	'	'
Common stock issued at incorporation (in shares)	'	'	1,000	'	'
Aggregate purchase price of common stock issued at incorporation (in dollars)	'	'	$10	'	$295,631,000
Common stock issued in connection with reorganization transaction to holders of Class A limited partner interest and Class B interests of certain holdings (in shares)	'	960,907	'	'	'
Issue price of IPO (in dollars per share)	$20	'	'	'	'
Stock split ratio	65.266	'	'	'	65.266
Outstanding common stock shares prior to closing of IPO	66,339,615	'	'	'	'
Shares of common stock issued in IPO	15,789,474	'	'	'	'
Net proceeds from IPO, after deducting underwriting discounts and commissions and offering expenses (in dollars)	295,600,000	'	'	'	296,044,000
Stockholders' equity	'	'	'	'	'
Reclassification from "Retained earnings" to "Additional paid-in capital"	'	'	'	$12,500,000	'
Decrease in net income attributable to noncontrolling interest	'	'	'	'400000	'
Holdings	'	'	'	'	'
Stockholders' equity	'	'	'	'	'
Percentage of ownership noncontrolling interest	3.20%	'	'	2.20%	2.20%

Earnings_Per_Share_Details

Earnings Per Share (Details) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Aug. 07, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Apr. 30, 2013
Earnings Per Share	'	'	'	'	'	'
Outstanding common stock prior to consummation of IPO (in shares)	'	'	'	'	'	960,907
Issue price of IPO (in dollars per share)	$20	'	'	'	'	'
Stock split ratio	65.266	'	'	65.266	'	'
Outstanding common stock shares prior to closing of IPO	66,339,615	'	'	'	'	'
Numerator:	'	'	'	'	'	'
Undistributed net income (loss) attributable to stockholders	'	$2,482	($2,096)	$37,058	$42,508	'
Participation rights of unvested RSUs in undistributed earnings	'	-6	'	-6	'	'
Basic undistributed net income (loss) attributable to stockholders	'	2,476	-2,096	37,052	42,508	'
Denominator:	'	'	'	'	'	'
Basic weighted average shares outstanding	'	76,637,000	66,340,000	69,810,000	66,340,000	'
Basic EPS attributable to stockholders (in dollars per share)	'	$0.03	($0.03)	$0.53	$0.64	'
Numerator:	'	'	'	'	'	'
Undisributed net income (loss) attributable to stockholders	'	2,482	-2,096	37,058	42,508	'
Participation rights of unvested RSUs in undistributed earnings	'	-6	'	-6	'	'
Effect of conversion of New Holdings Units to shares of Athlon's common stock	'	-215	'	616	'	'
Diluted undistributed net income (loss) attributable to stockholders	'	$2,261	($2,096)	$37,668	$42,508	'
Denominator:	'	'	'	'	'	'
Basic weighted average shares outstanding	'	76,637,000	66,340,000	69,810,000	66,340,000	'
Effect of conversion of New Holdings Units to shares of Athlon's common stock	'	1,856,000	'	1,856,000	1,856,000	'
Diluted weighted average shares outstanding	'	78,493,000	66,340,000	71,666,000	68,196,000	'
Diluted EPS attributable to stockholders (in dollars per share)	'	$0.03	($0.03)	$0.53	$0.62	'
Antidilutive New Holdings Units excluded from EPS calculations (in shares)	'	'	1,855,563	'	'	'

Incentive_Stock_Plans_Details

Incentive Stock Plans (Details) (USD $)	9 Months Ended									0 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Aug. 07, 2013
			RSUs	2013 Incentive Award Plan	2013 Incentive Award Plan	Maximum	Maximum	Class B limited partners	Class B limited partners	Holdings
					RSUs	2013 Incentive Award Plan	2013 Incentive Award Plan
							Non-employee directors
Incentive stock plans	'	'	'	'	'	'	'	'	'	'
Aggregate shares of common stock available for issuance under the 2013 stock incentive plan	'	'	'	8,400,000	'	'	'	'	'	'
Aggregate shares of common stock available for issuance under the 2013 stock incentive plan at January 1, 2014 under first condition	'	'	'	'	'	12,000,000	'	'	'	'
Percentage increase to shares of common stock available for issuance under the 2013 stock incentive plan at January 1, 2014 under second condition	'	'	'	'	'	4.00%	'	'	'	'
Grant date fair value of awards	'	'	'	'	'	'	$700,000	'	'	'
Remaining shares available for grant	'	'	'	7,776,087	'	'	'	'	'	'
Non-cash equity-based compensation expense	1,799,000	118,000	'	492,000	'	'	'	1,300,000	186,000	1,500,000
Capitalized non-cash equity-based compensation expense	'	'	'	37,000	'	'	'	421,000	68,000	'
Vesting period of RSU's	'	'	'	'	'3 years	'	'	'	'	'
Unvested RSUs	'	'	'	'	'	'	'	'	'	'
Granted (in shares)	'	'	'	'	623,913	'	'	'	'	'
Outstanding at ending of period	'	'	'	'	623,913	'	'	'	'	'
Weighted - Average Grant Date Fair Value	'	'	'	'	'	'	'	'	'	'
Granted (in dollars per share)	'	'	'	'	$32.21	'	'	'	'	'
Outstanding at the end of the period	'	'	'	'	$32.21	'	'	'	'	'
Additional disclosure	'	'	'	'	'	'	'	'	'	'
Unvested RSUs granted, vesting of which is dependent on passage of specified time and continued employment condition (in shares)	'	'	'	'	396,413	'	'	'	'	'
Unvested RSUs granted, vesting of which is dependent on passage of specified time and continued employment and also on performance condition (in shares)	'	'	'	'	227,500	'	'	'	'	'
Unvested RSUs subject to variable accounting (in shares)	'	'	0	'	'	'	'	'	'	'
Total unrecognized compensation cost related to unvested RSU's	'	'	'	'	$17,900,000	'	'	'	'	'
Weighted-average period for recognition of unrecognized compensation cost	'	'	'	'	'2 years 9 months 18 days	'	'	'	'	'

Related_Party_Transactions_Det

Related Party Transactions (Details) (USD $)	3 Months Ended	9 Months Ended					35 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Aug. 07, 2013	Sep. 30, 2013	Sep. 30, 2013
			Apollo Global Securities, LLC	Holdings	Holdings	Holdings	Holdings	Holdings	Holdings
					Apollo	Apollo	Apollo	Apollo funds	Other Class A limited partners
Related party transactions	'	'	'	'	'	'	'	'	'
Transaction fee as a percentage of total equity contributed	'	'	'	'	2.00%	'	'	'	'
Transaction fees	'	'	'	'	'	'	$7,500,000	'	'
Consulting and advisory fee as percentage of EBITDAX under first condition	'	'	'	'	1.00%	'	'	'	'
Advisory fee per quarter under second condition	'	'	'	'	62,500	'	'	'	'
Maximum advisory fee per calendar year	'	'	'	'	500,000	'	'	'	'
Advisory fee	'	'	'	'	500,000	493,000	'	'	'
Termination charges	2,408,000	2,408,000	'	'	2,400,000	'	'	'	'
Unreimbursed fee on termination of the service agreement	'	'	'	'	132,000	'	'	'	'
Proceeds from gross spread	'	'	500,000	'	'	'	'	'	'
Payment of discounts and commissions to underwriters in IPO	'	'	900,000	'	'	'	'	'	'
Distribution payment to Class A limited partners	'	$75,000,000	'	'	'	'	'	$73,000,000	$2,000,000
Number of common stock exchangeable against each unit	'	'	'	1	'	'	'	'	'
Percentage of income tax benefits distributable to holders of New Holdings Units	'	'	'	85.00%	'	'	'	'	'

Subsequent_Events_Details

Subsequent Events (Details) (Credit agreement, Holdings, USD $)	Sep. 30, 2013	31-May-13	Apr. 30, 2013	Nov. 30, 2013	Nov. 14, 2013
In Millions, unless otherwise specified				Subsequent events	Subsequent events
Subsequent events	'	'	'	'	'
Current borrowing base	$320	$320	$267.50	$525	'
Outstanding letters of credit	$0	'	'	'	$0