Summary of Significant Accounting Policies (Policies)	12 Months Ended
Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business combinations policy	The consolidated financial statements include the accounts of WGP and entities in which it holds a controlling financial interest, including WES and WES GP. All significant intercompany transactions have been eliminated. Investments in non-controlled entities over which WES, or WGP through its investment in WES, exercises significant influence are accounted for under the equity method. WGP proportionately consolidates WES’s 33.75% share of the assets, liabilities, revenues and expenses attributable to the Non-Operated Marcellus Interest systems and Anadarko-Operated Marcellus Interest systems (see Note 2) and WES’s 50% share of the assets, liabilities, revenues and expenses attributable to the Newcastle system in the accompanying consolidated financial statements. The consolidated financial results of WES are included in WGP’s consolidated financial statements due to WGP’s 100% ownership interest in WES GP and WES GP’s control of WES. Throughout these notes to consolidated financial statements, and to the extent material, any differences between the consolidated financial results of WGP and WES are discussed separately. WGP has no independent operations or material assets other than its partnership interests in WES. WGP’s consolidated financial statements differ from those of WES primarily as a result of (i) the presentation of noncontrolling interest ownership (attributable to the limited partner interests in WES held by the public and other subsidiaries of Anadarko), (ii) the elimination of WES GP’s investment in WES with WES GP’s underlying capital account, (iii) income tax expense and liabilities incurred by WGR Holdings, LLC, computed on a separate-return basis prior to its conversion into a limited partnership, and (iv) the general and administrative expenses incurred by WGP, which are separate from, and in addition to, those incurred by WES. Presentation of WES assets. The term “WES assets” refers to the assets indirectly owned and interests accounted for under the equity method (see Note 10) by WGP through its partnership interests in WES as of December 31, 2014. Because WGP owns the entire interest in and controls WES GP, and WGP GP is owned and controlled by Anadarko, each of WES’s acquisitions of WES assets from Anadarko has been considered a transfer of net assets between entities under common control. As such, WES assets acquired from Anadarko were initially recorded at Anadarko’s historic carrying value, which did not correlate to the total acquisition price paid by WES (see Note 2). Further, after an acquisition of WES assets from Anadarko, WES and WGP (by virtue of its consolidation of WES) may be required to recast their financial statements to include the activities of such WES assets from the date of common control. For those periods requiring recast, the consolidated financial statements for periods prior to the acquisition of WES assets from Anadarko have been prepared from Anadarko’s historical cost-basis accounts and may not necessarily be indicative of the actual results of operations that would have occurred if WES had owned the WES assets during the periods reported. Net income attributable to the WES assets acquired from Anadarko for periods prior to WES’s acquisition of the WES assets is not allocated to the limited partners. DBM acquisition. The DBM acquisition has been accounted for under the acquisition method of accounting. The assets acquired and liabilities assumed in the DBM acquisition were recorded in the consolidated balance sheet at their estimated fair values as of the acquisition date. Results of operations attributable to the DBM acquisition were included in the consolidated statement of income beginning on the acquisition date in the fourth quarter of 2014.
Noncontrolling interests policy	Noncontrolling interests. The interests in Chipeta Processing LLC (“Chipeta”) held by a third-party member and the limited partner interests in WES held by other subsidiaries of Anadarko and the public are reflected as noncontrolling interests in the consolidated financial statements. Chipeta. In July 2009, WES acquired a 51% interest in Chipeta and became party to Chipeta’s limited liability company agreement (the “Chipeta LLC agreement”). On August 1, 2012, WES acquired Anadarko’s then-remaining 24% membership interest in Chipeta (the “additional Chipeta interest”). Prior to this transaction, the interests in Chipeta held by Anadarko and a third-party member were reflected as noncontrolling interests in the consolidated financial statements. The acquisition of the additional Chipeta interest was accounted for on a prospective basis as WES acquired an additional interest in an already-consolidated entity. As such, effective August 1, 2012, noncontrolling interests excludes the financial results and operations of the additional Chipeta interest. The remaining 25% membership interest held by the third-party member is reflected within noncontrolling interests in the consolidated financial statements for all periods presented. See Note 2. WES. The publicly held limited partner interests in WES are reflected as noncontrolling interests in the consolidated financial statements for all periods presented. In addition, as part of the consideration paid for the acquisitions of the Anadarko-Operated Marcellus Interest and TEFR Interests, WES issued 757,619 WES common units to other subsidiaries of Anadarko. Also, as part of the consideration paid for the acquisition of DBM, WES issued 10,913,853 WES Class C units to a subsidiary of Anadarko. See Note 2 and Note 4. The limited partner interests in WES held by other subsidiaries of Anadarko are reflected within noncontrolling interests in the consolidated financial statements as of and for the years ended December 31, 2014 and 2013. The difference between the carrying value of WGP’s investment in WES and the underlying book value of common units issued by WES is accounted for as an equity transaction. Thus, if WES issues common units at a price different than WGP’s per-unit carrying value, any resulting change in the carrying value of WGP’s investment in WES is reflected as an adjustment to partners’ capital.
Use of estimates policy	Use of estimates. In preparing financial statements in accordance with GAAP, management makes informed judgments and estimates that affect the reported amounts of assets, liabilities, revenues, and expenses. Management evaluates its estimates and related assumptions regularly, using historical experience and other methods considered reasonable under the particular circumstances. Changes in facts and circumstances or additional information may result in revised estimates and actual results may differ from these estimates. Effects on the business, financial condition and results of operations resulting from revisions to estimates are recognized when the facts that give rise to the revisions become known.
Fair value policy	Fair value. The fair-value-measurement standard defines fair value 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. The standard characterizes inputs used in determining fair value according to a hierarchy that prioritizes those inputs based upon the degree to which they are observable. The three levels of the fair value hierarchy are as follows: Level 1 – Inputs represent quoted prices in active markets for identical assets or liabilities. Level 2 – Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly (for example, quoted market prices for similar assets or liabilities in active markets or quoted market prices for identical assets or liabilities in markets not considered to be active, inputs other than quoted prices that are observable for the asset or liability, or market-corroborated inputs). Level 3 – Inputs that are not observable from objective sources, such as management’s internally developed assumptions used in pricing an asset or liability (for example, an estimate of future cash flows used in management’s internally developed present value of future cash flows model that underlies the fair value measurement). Nonfinancial assets and liabilities initially measured at fair value include certain assets and liabilities acquired in a third-party business combination, assets and liabilities exchanged in non-monetary transactions, long-lived assets (asset groups), goodwill and other intangibles, initial recognition of asset retirement obligations, and initial recognition of environmental obligations assumed in a third-party acquisition. Impairment analyses for long-lived assets, goodwill and other intangibles, and the initial recognition of asset retirement obligations and environmental obligations use Level 3 inputs. When a fair value measurement is required and there is not a market-observable price for the asset or liability or a market-observable price for a similar asset or liability, the cost, income, or market valuation approach is used, depending on the quality of information available to support management’s assumptions. The fair value of debt reflects any premium or discount for the difference between the stated interest rate and the quarter-end market interest rate, and is based on quoted market prices for identical instruments, if available, or based on valuations of similar debt instruments. See Note 13. The carrying amounts of cash and cash equivalents, accounts receivable and accounts payable reported on the consolidated balance sheets approximate fair value due to the short-term nature of these items. The purchase price allocation is based on an assessment of the fair value of the assets acquired and liabilities assumed in the DBM acquisition using inputs that are not observable in the market and thus represent Level 3 inputs. The fair values of the processing plants, gathering system, and related facilities and equipment are based on market and cost approaches. The fair value of the intangible assets was determined using an income approach. Deferred taxes represent the tax effects of differences in the tax basis and acquisition-date fair value of the assets acquired and liabilities assumed. WES Class C unit distributions. WES’s Class C units receive quarterly distributions at a rate equivalent to WES’s common units. The distributions are paid in the form of additional Class C units (“PIK C units”) until the end of 2017 (unless earlier converted, see Note 4), and the Class C units are disregarded with respect to WES’s distribution of WES’s available cash until they are converted to common units. The number of additional PIK C units to be issued in connection with a distribution payable on the Class C units is determined by dividing the corresponding distribution attributable to the Class C units by the volume-weighted-average price of WES’s common units for the ten days immediately preceding the payment date for the WES common unit distribution, less a 6% discount. WES records the PIK C distributions at fair value at the time of issuance. This fair value measurement uses WES’s unit price as a significant input in the determination of the fair value and thus represents a Level 2 measurement. On February 12, 2015, WES GP distributed 45,711 PIK C units to the Class C unitholder, based on the $0.700 common unit distribution referenced above, with an implied fair value of $3.1 million. The Class C unit distribution was prorated for the 37-day period the Class C units were outstanding during the fourth quarter of 2014. WES note receivable from Anadarko. Concurrently with the closing of WES’s May 2008 IPO, WES loaned $260.0 million to Anadarko in exchange for a 30-year note bearing interest at a fixed annual rate of 6.50%, payable quarterly. The fair value of the note receivable from Anadarko was $317.8 million and $296.7 million at December 31, 2014 and 2013, respectively. The fair value of the note reflects consideration of credit risk and any premium or discount for the differential between the stated interest rate and quarter-end market interest rate, based on quoted market prices of similar debt instruments. Accordingly, the fair value of the note receivable from Anadarko is measured using Level 2 inputs. During 2014, WES recognized impairments of $3.1 million, primarily related to a non-operational plant in the Powder River Basin that was impaired to its estimated fair value of $2.4 million, using Level 3 fair-value inputs, the cancellation of various capital projects by the third-party operator of the Non-Operated Marcellus Interest systems and a compressor no longer in service at the Hilight system. During 2012, WES recognized a $6.0 million impairment related to a gathering system in central Wyoming that was impaired to its estimated fair value using Level 3 fair-value inputs and an impairment of $0.6 million for the original installation costs on a compressor relocated within WES’s operating assets.
Cash equivalents policy	Cash equivalents. All highly liquid investments with a maturity of three months or less when purchased are considered to be cash equivalents.
Bad-debt reserve policy	Bad-debt reserve. Revenues are primarily from Anadarko, for which no credit limit is maintained. Exposure to bad debts is analyzed on a customer-by-customer basis for its third-party accounts receivable and may establish credit limits for significant third-party customers. As of December 31, 2014 and 2013, bad-debt reserve was immaterial.
Natural gas imbalances policy	Natural gas imbalances. The consolidated balance sheets include natural gas imbalance receivables and payables resulting from differences in gas volumes received into WES’s systems and gas volumes delivered by WES to customers’ pipelines. Natural gas volumes owed to or by WES that are subject to monthly cash settlement are valued according to the terms of the contract as of the balance sheet dates and reflect market index prices. Other natural gas volumes owed to or by WES are valued at the weighted-average cost of natural gas as of the balance sheet dates and are settled in-kind. As of December 31, 2014, natural gas imbalance receivables and payables were $0.4 million and $0.7 million, respectively. As of December 31, 2013, natural gas imbalance receivables and payables were $3.6 million and $2.5 million, respectively. Changes in natural gas imbalances are reported in other revenues for imbalance receivables or in cost of product for imbalance payables.
Inventory policy	Inventory. The cost of NGLs inventories is determined by the weighted-average cost method on a location-by-location basis. Inventory is stated at the lower of weighted-average cost or market value and is reported in other current assets in the consolidated balance sheets. See Note 11.
Property, plant and equipment policy	Property, plant and equipment. Property, plant and equipment are generally stated at the lower of historical cost less accumulated depreciation or fair value, if impaired. Because acquisitions of assets from Anadarko are transfers of net assets between entities under common control, the assets acquired from Anadarko are initially recorded at Anadarko’s historic carrying value. The difference between the carrying value of net assets acquired from Anadarko and the consideration paid is recorded as an adjustment to partners’ capital. Assets acquired in a business combination or non-monetary exchange with a third party are initially recorded at fair value. All construction-related direct labor and material costs are capitalized. The cost of renewals and betterments that extend the useful life of property, plant and equipment is also capitalized. The cost of repairs, replacements and major maintenance projects that do not extend the useful life or increase the expected output of property, plant and equipment is expensed as incurred. Depreciation is computed using the straight-line method based on estimated useful lives and salvage values of assets. However, subsequent events could cause a change in estimates, thereby impacting future depreciation amounts. Uncertainties that may impact these estimates include, but are not limited to, changes in laws and regulations relating to environmental matters, including air and water quality, restoration and abandonment requirements, economic conditions, and supply and demand in the area. Management evaluates the ability to recover the carrying amount of its long-lived assets to determine whether its long-lived assets have been impaired. Impairments exist when the carrying amount of an asset exceeds estimates of the undiscounted cash flows expected to result from the use and eventual disposition of the asset. When alternative courses of action to recover the carrying amount of a long-lived asset are under consideration, estimates of future undiscounted cash flows take into account possible outcomes and probabilities of their occurrence. If the carrying amount of the long-lived asset is not recoverable based on the estimated future undiscounted cash flows, the impairment loss is measured as the excess of the asset’s carrying amount over its estimated fair value, such that the asset’s carrying amount is adjusted to its estimated fair value with an offsetting charge to impairment expense. Refer to Note 8 for a description of impairments recorded during the years ended December 31, 2014, 2013 and 2012. Contributions in aid of construction costs from affiliates. In 2013, a subsidiary of Anadarko entered into an aid in construction agreement with WES, whereby WES constructed five receipt-point facilities at its Brasada complex that serve the Anadarko subsidiary. Such subsidiary reimbursed WES for costs associated with construction of the receipt points. These reimbursements are presented within the investing section of the consolidated statements of cash flows as “Contributions in aid of construction costs from affiliates.”
Capitalized interest policy	Capitalized interest. Interest is capitalized as part of the historical cost of constructing assets for significant projects that are in progress. Capitalized interest is determined by multiplying WES’s weighted-average borrowing cost on debt by the average amount of qualifying costs incurred. Once the construction of an asset subject to interest capitalization is completed and the asset is placed in service, the associated capitalized interest is expensed through depreciation or impairment, together with other capitalized costs related to that asset.
Goodwill policy	Goodwill. Goodwill is recorded when the purchase price of a business acquired exceeds the fair market value of the tangible and separately measurable intangible net assets. Refer to Note 9 for a discussion of goodwill. Goodwill is evaluated for impairment annually, as of October 1, or more often as facts and circumstances warrant. WES has allocated goodwill on its two reporting units: (i) gathering and processing and (ii) transportation. An initial qualitative assessment may be performed prior to proceeding to the comparison of the fair value of each reporting unit to which goodwill has been assigned, to the carrying amount of net assets, including goodwill, of each reporting unit. If concluded, based on qualitative factors, that it is more likely than not that the fair value of the reporting unit exceeds its carrying amount, then goodwill is not impaired, and estimating the fair value of the reporting unit is not necessary. If the carrying amount of the reporting unit exceeds its fair value, goodwill is written down to its implied fair value through a charge to operating expense based on a hypothetical purchase price allocation. The carrying value of goodwill after such an impairment would represent a Level 3 fair value measurement.
Other intangible assets policy	Other intangible assets. WES assesses intangible assets, as described in Note 9, for impairment together with related underlying long-lived assets whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. See Property, plant and equipment within this Note 1 for further discussion of management’s process to evaluate potential impairment of long-lived assets.
Asset retirement obligations and environmental expenditures policy	Asset retirement obligations. Management recognizes a liability based on the estimated costs of retiring tangible long-lived assets. The liability is recognized at fair value, measured using discounted expected future cash outflows for the asset retirement obligation when the obligation originates, which generally is when an asset is acquired or constructed. The carrying amount of the associated asset is increased commensurate with the liability recognized. Over time, the discounted liability is adjusted to its expected settlement value through accretion expense, which is reported within depreciation, amortization and impairments in the consolidated statements of income. Subsequent to the initial recognition, the liability is also adjusted for any changes in the expected value of the retirement obligation (with a corresponding adjustment to property, plant and equipment) until the obligation is settled. Revisions in estimated asset retirement obligations may result from changes in estimated inflation rates, discount rates, asset retirement costs and the estimated timing of settling asset retirement obligations. See Note 12. Environmental expenditures. WES expenses environmental obligations related to conditions caused by past operations that do not generate current or future revenues. Environmental obligations related to operations that generate current or future revenues are expensed or capitalized, as appropriate. Liabilities are recorded when the necessity for environmental remediation or other potential environmental liabilities becomes probable and the costs can be reasonably estimated. Accruals for estimated losses from environmental remediation obligations are recognized no later than at the time of the completion of the remediation feasibility study. These accruals are adjusted as additional information becomes available or as circumstances change. Costs of future expenditures for environmental-remediation obligations are not discounted to their present value. See Note 14.
Segments policy	Segments. Because WGP reflects its ownership interest in WES on a consolidated basis, and has no independent operations or material assets outside those of WES, WGP’s segment analysis and presentation is the same as that of WES. WES’s operations are organized into a single operating segment, the assets of which gather, process, compress, treat and transport Anadarko and third-party natural gas, condensate, NGLs and crude oil in the United States.
Revenues and cost of product policy	Revenues and cost of product. Under its fee-based gathering, treating and processing arrangements, WES is paid a fixed fee based on the volume and thermal content of natural gas and recognizes revenues for its services in the month such services are performed. Producers’ wells are connected to WES’s gathering systems for delivery of natural gas to WES’s processing or treating plants, where the natural gas is processed to extract NGLs and condensate or treated in order to satisfy pipeline specifications. In some areas, where no processing is required, the producers’ gas is gathered and delivered to pipelines for market delivery. Under cost-of-service gathering agreements, fees are earned for gathering and compression services based on rates calculated in a cost-of-service model and reviewed periodically over the life of the agreements. Under percent-of-proceeds contracts, revenue is recognized when the natural gas, NGLs or condensate are sold. The percentage of the product sale ultimately paid to the producer is recorded as a related cost of product expense. WES purchases natural gas volumes at the wellhead for gathering and processing. As a result, WES has volumes of NGLs and condensate to sell and volumes of residue to either sell, to use for system fuel or to satisfy keep-whole obligations. In addition, depending upon specific contract terms, condensate and NGLs recovered during gathering and processing are either returned to the producer or retained and sold. Under keep-whole contracts, when condensate or NGLs are retained and sold, producers are kept whole for the condensate or NGL volumes through the receipt of a thermally equivalent volume of residue. The keep-whole contract conveys an economic benefit to WES when the combined value of the individual NGLs is greater in the form of liquids than as a component of the natural gas stream; however, WES is adversely impacted when the value of the NGLs is lower than the value of the natural gas stream including the liquids. WES has commodity price swap agreements with Anadarko to mitigate exposure to a substantial majority of the commodity price uncertainty that would otherwise be present as a result of the purchase and sale of natural gas, condensate or NGLs. See Note 5. Revenue is recognized from the sale of condensate and NGLs upon transfer of title and related purchases are recorded as cost of product. WES earns transportation revenues through firm contracts that obligate each of its customers to pay a monthly reservation or demand charge regardless of the pipeline capacity used by that customer. An additional commodity usage fee is charged to the customer based on the actual volume of natural gas transported. Transportation revenues are also generated from interruptible contracts pursuant to which a fee is charged to the customer based on volumes transported through the pipeline. Revenues for transportation of natural gas and NGLs are recognized over the period of firm transportation contracts or, in the case of usage fees and interruptible contracts, when the volumes are received into the pipeline. From time to time, certain revenues may be subject to refund pending the outcome of rate matters before the Federal Energy Regulatory Commission (the “FERC”) and reserves are established where appropriate. Proceeds from the sale of residue, NGLs and condensate are reported as revenues from natural gas, natural gas liquids and condensate sales in the consolidated statements of income. Revenues attributable to the fixed-fee component of gathering and processing contracts as well as demand charges and commodity usage fees on transportation contracts are reported as revenues from gathering, processing and transportation of natural gas and natural gas liquids in the consolidated statements of income.
Equity-based compensation policy	Equity-based compensation. Concurrently with WGP’s IPO, WGP GP adopted the Western Gas Equity Partners, LP 2012 Long-Term Incentive Plan (the “WGP LTIP”). The WGP LTIP permits the issuance of up to 3,000,000 WGP common units, of which 2,959,364 units remained available for future issuance as of December 31, 2014. Upon vesting of each phantom unit, the holder will receive common units of WGP or, at the discretion of WGP GP’s Board of Directors, cash in an amount equal to the market value of common units of WGP on the vesting date. Equity-based compensation expense attributable to grants made under the WGP LTIP impacts cash flows from operating activities only to the extent cash payments are made to a participant in lieu of issuance of WGP common units to the participant. Stock-based compensation expense attributable to awards granted under the WGP LTIP is amortized over the vesting periods applicable to the awards. The Western Gas Partners, LP 2008 Long-Term Incentive Plan (the “WES LTIP”) was adopted by WES GP concurrently with the IPO of WES and permits the issuance of up to 2,250,000 WES common units, of which 2,133,227 units remained available for future issuance as of December 31, 2014. Upon vesting of each phantom unit award, the holder will receive common units of WES or, at the discretion of WES GP’s Board of Directors, cash in an amount equal to the market value of common units of WES on the vesting date. Equity-based compensation expense attributable to grants made under the WES LTIP impact cash flows from operating activities only to the extent cash payments are made to a participant in lieu of issuance of common units to the participant. Stock-based compensation expense attributable to awards granted under the WES LTIP is amortized over the vesting periods applicable to the awards. Additionally, general and administrative expenses include equity-based compensation costs allocated by Anadarko for grants made pursuant to (i) the Western Gas Holdings, LLC Equity Incentive Plan, as amended and restated (the “Incentive Plan”) for the year ended December 31, 2012 and (ii) the Anadarko Petroleum Corporation 1999 Stock Incentive Plan and the Anadarko Petroleum Corporation 2008 and 2012 Omnibus Incentive Compensation Plans (Anadarko’s plans are referred to collectively as the “Anadarko Incentive Plans”) for all periods presented. Grants made under equity-based compensation plans result in equity-based compensation expense, which is determined by reference to the fair value of equity compensation. For equity-based awards ultimately settled through the issuance of units or stock, the fair value is measured as of the date of the relevant equity grant. Equity-based compensation granted under the Anadarko Incentive Plans does not impact cash flows from operating activities since the offset to compensation expense is recorded as a contribution to partners’ capital in the consolidated financial statements at the time of contribution, when the expense is realized. However, distribution equivalent rights awarded in tandem with equity-or liability-based awards are paid in cash and reflected within financing cash flows in the consolidated statements of cash flows. See Note 6.
Income taxes policy	WES income taxes. WES generally is not subject to federal income tax or state income tax other than Texas margin tax on the portion of its income that is apportionable to Texas. Deferred state income taxes are recorded on temporary differences between the financial statement carrying amounts of assets and liabilities and their respective tax bases. WES routinely assesses the realizability of its deferred tax assets. If WES concludes that it is more likely than not that some of the deferred tax assets will not be realized, the tax asset is reduced by a valuation allowance. Federal and state current and deferred income tax expense was recorded on WES assets prior to WES’s acquisition of these assets from Anadarko. For periods beginning on and subsequent to WES’s acquisition of the WES assets, WES makes payments to Anadarko pursuant to the tax sharing agreement entered into between Anadarko and WES for its estimated share of taxes from all forms of taxation, excluding taxes imposed by the United States, that are included in any combined or consolidated returns filed by Anadarko. The aggregate difference in the basis of WES’s assets for financial and tax reporting purposes cannot be readily determined as WES does not have access to information about each partner’s tax attributes in WES. The accounting standards for uncertain tax positions defines the criteria an individual tax position must satisfy for any part of the benefit of that position to be recognized in the financial statements. WES had no material uncertain tax positions at December 31, 2014 or 2013. With respect to assets acquired from Anadarko, WES recorded Anadarko’s historic current and deferred income taxes for the periods prior to WES’s ownership of the assets. For periods subsequent to WES’s acquisition, WES is not subject to tax except for the Texas margin tax and, accordingly, does not record current and deferred federal income taxes related to the assets acquired from Anadarko. WGP income taxes. Prior to its September 2012 conversion from a limited liability company to a limited partnership, WGP was WGR Holdings, LLC, a single-member Delaware limited liability company treated as a division of Anadarko and disregarded for U.S. federal income tax purposes. As such, WGR Holdings, LLC was included in Anadarko’s consolidated income tax return for federal and state income tax purposes. In addition to WES’s historic Texas margin tax expense and liabilities, the accompanying consolidated financial statements of WGP include income tax expense and liabilities incurred by WGR Holdings, LLC, computed on a separate-return basis. Deferred federal and state income taxes included in the accompanying consolidated financial statements are attributable to temporary differences between the financial statement carrying amount and tax basis of WGP’s investment in WES. WGP’s accounting policy is to “look through” its investment in WES for purposes of calculating deferred income tax asset and liability balances attributable to WGP’s interests in WES. The application of such accounting policy resulted in no deferred income taxes being recognized for the book and tax basis difference in goodwill, which is non-deductible for tax purposes for all periods presented. WGP had no material uncertain tax positions at December 31, 2014 or 2013.
Net income per common unit policy	Net income per common unit. Earnings per unit is calculated by dividing the limited partners’ interest in net income by the weighted-average number of common units outstanding. Net income per common unit is calculated assuming that cash distributions are equal to the net income attributable to WGP. Net income attributable to periods prior to WGP’s IPO is not allocated to the limited partners for purposes of calculating net income per unit. As a result, pre-IPO net income, representing the financial results prior to WGP’s IPO on December 12, 2012, has been excluded from the limited partners’ interest in net income. Net income equal to the amount of available cash (as defined in WGP’s partnership agreement) is allocated to the common unitholders consistent with actual cash distributions. See Note 4.
Recently issued accounting standards policy	Recently issued accounting standards. Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers, supersedes the revenue recognition requirements in Topic 605, Revenue Recognition, and industry-specific guidance in Subtopic 932-605, Extractive Activities—Oil and Gas—Revenue Recognition, and requires an entity to recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This ASU is effective for annual and interim periods beginning in 2017 and is required to be adopted using one of two retrospective application methods, with no early adoption permitted. WGP is currently evaluating the impact of the adoption of this ASU on its consolidated financial statements. ASU 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity, changes the criteria for reporting discontinued operations and requires additional disclosures, both for discontinued operations and for individually significant dispositions and assets classified as held for sale not qualifying as discontinued operations. This ASU is effective for annual and interim periods beginning in 2015, with early adoption permitted for disposals or for assets classified as held for sale that have not been reported in previously issued financial statements. WGP early adopted this ASU on a prospective basis beginning with the first quarter of 2014. The adoption did not have a material impact on WGP’s consolidated financial statements. ASU 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists, requires that an unrecognized tax benefit, or a portion of an unrecognized tax benefit, be presented in the financial statements as a reduction to a deferred tax asset, except in certain circumstances. This ASU is effective for annual and interim periods beginning in 2014. WGP adopted this ASU on a prospective basis beginning with the first quarter of 2014. The adoption did not have a material impact on WGP’s consolidated financial statements. See Note 7—Income Taxes.
Equity investments policy	Management evaluates its equity investments for impairment whenever events or changes in circumstances indicate that the carrying value of such investments may have experienced a decline in value that is other than temporary. When evidence of loss in value has occurred, management compares the estimated fair value of the investment to the carrying value of the investment to determine whether the investment has been impaired. Management assesses the fair value of equity investments using commonly accepted techniques, and may use more than one method, including, but not limited to, recent third-party comparable sales and discounted cash flow models. If the estimated fair value is less than the carrying value, the excess of the carrying value over the estimated fair value is recognized as an impairment loss.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2014

Organization, Consolidation and Presentation of Financial Statements [Abstract]

The consolidated financial statements include the accounts of WGP and entities in which it holds a controlling financial interest, including WES and WES GP. All significant intercompany transactions have been eliminated. Investments in non-controlled entities over which WES, or WGP through its investment in WES, exercises significant influence are accounted for under the equity method. WGP proportionately consolidates WES’s 33.75% share of the assets, liabilities, revenues and expenses attributable to the Non-Operated Marcellus Interest systems and Anadarko-Operated Marcellus Interest systems (see Note 2) and WES’s 50% share of the assets, liabilities, revenues and expenses attributable to the Newcastle system in the accompanying consolidated financial statements.

The consolidated financial results of WES are included in WGP’s consolidated financial statements due to WGP’s 100% ownership interest in WES GP and WES GP’s control of WES. Throughout these notes to consolidated financial statements, and to the extent material, any differences between the consolidated financial results of WGP and WES are discussed separately. WGP has no independent operations or material assets other than its partnership interests in WES. WGP’s consolidated financial statements differ from those of WES primarily as a result of (i) the presentation of noncontrolling interest ownership (attributable to the limited partner interests in WES held by the public and other subsidiaries of Anadarko), (ii) the elimination of WES GP’s investment in WES with WES GP’s underlying capital account, (iii) income tax expense and liabilities incurred by WGR Holdings, LLC, computed on a separate-return basis prior to its conversion into a limited partnership, and (iv) the general and administrative expenses incurred by WGP, which are separate from, and in addition to, those incurred by WES.

Presentation of WES assets. The term “WES assets” refers to the assets indirectly owned and interests accounted for under the equity method (see Note 10) by WGP through its partnership interests in WES as of December 31, 2014. Because WGP owns the entire interest in and controls WES GP, and WGP GP is owned and controlled by Anadarko, each of WES’s acquisitions of WES assets from Anadarko has been considered a transfer of net assets between entities under common control. As such, WES assets acquired from Anadarko were initially recorded at Anadarko’s historic carrying value, which did not correlate to the total acquisition price paid by WES (see Note 2). Further, after an acquisition of WES assets from Anadarko, WES and WGP (by virtue of its consolidation of WES) may be required to recast their financial statements to include the activities of such WES assets from the date of common control.

For those periods requiring recast, the consolidated financial statements for periods prior to the acquisition of WES assets from Anadarko have been prepared from Anadarko’s historical cost-basis accounts and may not necessarily be indicative of the actual results of operations that would have occurred if WES had owned the WES assets during the periods reported. Net income attributable to the WES assets acquired from Anadarko for periods prior to WES’s acquisition of the WES assets is not allocated to the limited partners.

DBM acquisition. The DBM acquisition has been accounted for under the acquisition method of accounting. The assets acquired and liabilities assumed in the DBM acquisition were recorded in the consolidated balance sheet at their estimated fair values as of the acquisition date. Results of operations attributable to the DBM acquisition were included in the consolidated statement of income beginning on the acquisition date in the fourth quarter of 2014.

Noncontrolling interests policy

Noncontrolling interests. The interests in Chipeta Processing LLC (“Chipeta”) held by a third-party member and the limited partner interests in WES held by other subsidiaries of Anadarko and the public are reflected as noncontrolling interests in the consolidated financial statements.

Chipeta. In July 2009, WES acquired a 51% interest in Chipeta and became party to Chipeta’s limited liability company agreement (the “Chipeta LLC agreement”). On August 1, 2012, WES acquired Anadarko’s then-remaining 24% membership interest in Chipeta (the “additional Chipeta interest”). Prior to this transaction, the interests in Chipeta held by Anadarko and a third-party member were reflected as noncontrolling interests in the consolidated financial statements. The acquisition of the additional Chipeta interest was accounted for on a prospective basis as WES acquired an additional interest in an already-consolidated entity. As such, effective August 1, 2012, noncontrolling interests excludes the financial results and operations of the additional Chipeta interest. The remaining 25% membership interest held by the third-party member is reflected within noncontrolling interests in the consolidated financial statements for all periods presented. See Note 2.

WES. The publicly held limited partner interests in WES are reflected as noncontrolling interests in the consolidated financial statements for all periods presented. In addition, as part of the consideration paid for the acquisitions of the Anadarko-Operated Marcellus Interest and TEFR Interests, WES issued 757,619 WES common units to other subsidiaries of Anadarko. Also, as part of the consideration paid for the acquisition of DBM, WES issued 10,913,853 WES Class C units to a subsidiary of Anadarko. See Note 2 and Note 4. The limited partner interests in WES held by other subsidiaries of Anadarko are reflected within noncontrolling interests in the consolidated financial statements as of and for the years ended December 31, 2014 and 2013.

The difference between the carrying value of WGP’s investment in WES and the underlying book value of common units issued by WES is accounted for as an equity transaction. Thus, if WES issues common units at a price different than WGP’s per-unit carrying value, any resulting change in the carrying value of WGP’s investment in WES is reflected as an adjustment to partners’ capital.

Use of estimates policy

Use of estimates. In preparing financial statements in accordance with GAAP, management makes informed judgments and estimates that affect the reported amounts of assets, liabilities, revenues, and expenses. Management evaluates its estimates and related assumptions regularly, using historical experience and other methods considered reasonable under the particular circumstances. Changes in facts and circumstances or additional information may result in revised estimates and actual results may differ from these estimates. Effects on the business, financial condition and results of operations resulting from revisions to estimates are recognized when the facts that give rise to the revisions become known.

Fair value policy

Fair value. The fair-value-measurement standard defines fair value 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. The standard characterizes inputs used in determining fair value according to a hierarchy that prioritizes those inputs based upon the degree to which they are observable. The three levels of the fair value hierarchy are as follows:

Level 1 – Inputs represent quoted prices in active markets for identical assets or liabilities.

Level 2 – Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly (for example, quoted market prices for similar assets or liabilities in active markets or quoted market prices for identical assets or liabilities in markets not considered to be active, inputs other than quoted prices that are observable for the asset or liability, or market-corroborated inputs).

Level 3 – Inputs that are not observable from objective sources, such as management’s internally developed assumptions used in pricing an asset or liability (for example, an estimate of future cash flows used in management’s internally developed present value of future cash flows model that underlies the fair value measurement).

Nonfinancial assets and liabilities initially measured at fair value include certain assets and liabilities acquired in a third-party business combination, assets and liabilities exchanged in non-monetary transactions, long-lived assets (asset groups), goodwill and other intangibles, initial recognition of asset retirement obligations, and initial recognition of environmental obligations assumed in a third-party acquisition. Impairment analyses for long-lived assets, goodwill and other intangibles, and the initial recognition of asset retirement obligations and environmental obligations use Level 3 inputs. When a fair value measurement is required and there is not a market-observable price for the asset or liability or a market-observable price for a similar asset or liability, the cost, income, or market valuation approach is used, depending on the quality of information available to support management’s assumptions.

The fair value of debt reflects any premium or discount for the difference between the stated interest rate and the quarter-end market interest rate, and is based on quoted market prices for identical instruments, if available, or based on valuations of similar debt instruments. See Note 13.

The carrying amounts of cash and cash equivalents, accounts receivable and accounts payable reported on the consolidated balance sheets approximate fair value due to the short-term nature of these items.

The purchase price allocation is based on an assessment of the fair value of the assets acquired and liabilities assumed in the DBM acquisition using inputs that are not observable in the market and thus represent Level 3 inputs. The fair values of the processing plants, gathering system, and related facilities and equipment are based on market and cost approaches. The fair value of the intangible assets was determined using an income approach. Deferred taxes represent the tax effects of differences in the tax basis and acquisition-date fair value of the assets acquired and liabilities assumed.

WES Class C unit distributions. WES’s Class C units receive quarterly distributions at a rate equivalent to WES’s common units. The distributions are paid in the form of additional Class C units (“PIK C units”) until the end of 2017 (unless earlier converted, see Note 4), and the Class C units are disregarded with respect to WES’s distribution of WES’s available cash until they are converted to common units. The number of additional PIK C units to be issued in connection with a distribution payable on the Class C units is determined by dividing the corresponding distribution attributable to the Class C units by the volume-weighted-average price of WES’s common units for the ten days immediately preceding the payment date for the WES common unit distribution, less a 6% discount. WES records the PIK C distributions at fair value at the time of issuance. This fair value measurement uses WES’s unit price as a significant input in the determination of the fair value and thus represents a Level 2 measurement. On February 12, 2015, WES GP distributed 45,711 PIK C units to the Class C unitholder, based on the $0.700 common unit distribution referenced above, with an implied fair value of $3.1 million. The Class C unit distribution was prorated for the 37-day period the Class C units were outstanding during the fourth quarter of 2014.

WES note receivable from Anadarko. Concurrently with the closing of WES’s May 2008 IPO, WES loaned $260.0 million to Anadarko in exchange for a 30-year note bearing interest at a fixed annual rate of 6.50%, payable quarterly. The fair value of the note receivable from Anadarko was $317.8 million and $296.7 million at December 31, 2014 and 2013, respectively. The fair value of the note reflects consideration of credit risk and any premium or discount for the differential between the stated interest rate and quarter-end market interest rate, based on quoted market prices of similar debt instruments. Accordingly, the fair value of the note receivable from Anadarko is measured using Level 2 inputs.

During 2014, WES recognized impairments of $3.1 million, primarily related to a non-operational plant in the Powder River Basin that was impaired to its estimated fair value of $2.4 million, using Level 3 fair-value inputs, the cancellation of various capital projects by the third-party operator of the Non-Operated Marcellus Interest systems and a compressor no longer in service at the Hilight system.

During 2012, WES recognized a $6.0 million impairment related to a gathering system in central Wyoming that was impaired to its estimated fair value using Level 3 fair-value inputs and an impairment of $0.6 million for the original installation costs on a compressor relocated within WES’s operating assets.

Cash equivalents policy

Cash equivalents. All highly liquid investments with a maturity of three months or less when purchased are considered to be cash equivalents.

Bad-debt reserve policy

Bad-debt reserve. Revenues are primarily from Anadarko, for which no credit limit is maintained. Exposure to bad debts is analyzed on a customer-by-customer basis for its third-party accounts receivable and may establish credit limits for significant third-party customers. As of December 31, 2014 and 2013, bad-debt reserve was immaterial.

Natural gas imbalances policy

Natural gas imbalances. The consolidated balance sheets include natural gas imbalance receivables and payables resulting from differences in gas volumes received into WES’s systems and gas volumes delivered by WES to customers’ pipelines. Natural gas volumes owed to or by WES that are subject to monthly cash settlement are valued according to the terms of the contract as of the balance sheet dates and reflect market index prices. Other natural gas volumes owed to or by WES are valued at the weighted-average cost of natural gas as of the balance sheet dates and are settled in-kind. As of December 31, 2014, natural gas imbalance receivables and payables were $0.4 million and $0.7 million, respectively. As of December 31, 2013, natural gas imbalance receivables and payables were $3.6 million and $2.5 million, respectively. Changes in natural gas imbalances are reported in other revenues for imbalance receivables or in cost of product for imbalance payables.

Inventory policy

Inventory. The cost of NGLs inventories is determined by the weighted-average cost method on a location-by-location basis. Inventory is stated at the lower of weighted-average cost or market value and is reported in other current assets in the consolidated balance sheets. See Note 11.

Property, plant and equipment policy

Property, plant and equipment. Property, plant and equipment are generally stated at the lower of historical cost less accumulated depreciation or fair value, if impaired. Because acquisitions of assets from Anadarko are transfers of net assets between entities under common control, the assets acquired from Anadarko are initially recorded at Anadarko’s historic carrying value. The difference between the carrying value of net assets acquired from Anadarko and the consideration paid is recorded as an adjustment to partners’ capital.

Assets acquired in a business combination or non-monetary exchange with a third party are initially recorded at fair value. All construction-related direct labor and material costs are capitalized. The cost of renewals and betterments that extend the useful life of property, plant and equipment is also capitalized. The cost of repairs, replacements and major maintenance projects that do not extend the useful life or increase the expected output of property, plant and equipment is expensed as incurred.

Depreciation is computed using the straight-line method based on estimated useful lives and salvage values of assets. However, subsequent events could cause a change in estimates, thereby impacting future depreciation amounts. Uncertainties that may impact these estimates include, but are not limited to, changes in laws and regulations relating to environmental matters, including air and water quality, restoration and abandonment requirements, economic conditions, and supply and demand in the area.

Management evaluates the ability to recover the carrying amount of its long-lived assets to determine whether its long-lived assets have been impaired. Impairments exist when the carrying amount of an asset exceeds estimates of the undiscounted cash flows expected to result from the use and eventual disposition of the asset. When alternative courses of action to recover the carrying amount of a long-lived asset are under consideration, estimates of future undiscounted cash flows take into account possible outcomes and probabilities of their occurrence. If the carrying amount of the long-lived asset is not recoverable based on the estimated future undiscounted cash flows, the impairment loss is measured as the excess of the asset’s carrying amount over its estimated fair value, such that the asset’s carrying amount is adjusted to its estimated fair value with an offsetting charge to impairment expense. Refer to Note 8 for a description of impairments recorded during the years ended December 31, 2014, 2013 and 2012.

Contributions in aid of construction costs from affiliates. In 2013, a subsidiary of Anadarko entered into an aid in construction agreement with WES, whereby WES constructed five receipt-point facilities at its Brasada complex that serve the Anadarko subsidiary. Such subsidiary reimbursed WES for costs associated with construction of the receipt points. These reimbursements are presented within the investing section of the consolidated statements of cash flows as “Contributions in aid of construction costs from affiliates.”

Capitalized interest policy

Capitalized interest. Interest is capitalized as part of the historical cost of constructing assets for significant projects that are in progress. Capitalized interest is determined by multiplying WES’s weighted-average borrowing cost on debt by the average amount of qualifying costs incurred. Once the construction of an asset subject to interest capitalization is completed and the asset is placed in service, the associated capitalized interest is expensed through depreciation or impairment, together with other capitalized costs related to that asset.

Goodwill policy

Goodwill. Goodwill is recorded when the purchase price of a business acquired exceeds the fair market value of the tangible and separately measurable intangible net assets. Refer to Note 9 for a discussion of goodwill. Goodwill is evaluated for impairment annually, as of October 1, or more often as facts and circumstances warrant. WES has allocated goodwill on its two reporting units: (i) gathering and processing and (ii) transportation. An initial qualitative assessment may be performed prior to proceeding to the comparison of the fair value of each reporting unit to which goodwill has been assigned, to the carrying amount of net assets, including goodwill, of each reporting unit. If concluded, based on qualitative factors, that it is more likely than not that the fair value of the reporting unit exceeds its carrying amount, then goodwill is not impaired, and estimating the fair value of the reporting unit is not necessary. If the carrying amount of the reporting unit exceeds its fair value, goodwill is written down to its implied fair value through a charge to operating expense based on a hypothetical purchase price allocation. The carrying value of goodwill after such an impairment would represent a Level 3 fair value measurement.

Other intangible assets policy

Other intangible assets. WES assesses intangible assets, as described in Note 9, for impairment together with related underlying long-lived assets whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. See Property, plant and equipment within this Note 1 for further discussion of management’s process to evaluate potential impairment of long-lived assets.

Asset retirement obligations and environmental expenditures policy

Asset retirement obligations. Management recognizes a liability based on the estimated costs of retiring tangible long-lived assets. The liability is recognized at fair value, measured using discounted expected future cash outflows for the asset retirement obligation when the obligation originates, which generally is when an asset is acquired or constructed. The carrying amount of the associated asset is increased commensurate with the liability recognized. Over time, the discounted liability is adjusted to its expected settlement value through accretion expense, which is reported within depreciation, amortization and impairments in the consolidated statements of income. Subsequent to the initial recognition, the liability is also adjusted for any changes in the expected value of the retirement obligation (with a corresponding adjustment to property, plant and equipment) until the obligation is settled. Revisions in estimated asset retirement obligations may result from changes in estimated inflation rates, discount rates, asset retirement costs and the estimated timing of settling asset retirement obligations. See Note 12.

Environmental expenditures. WES expenses environmental obligations related to conditions caused by past operations that do not generate current or future revenues. Environmental obligations related to operations that generate current or future revenues are expensed or capitalized, as appropriate. Liabilities are recorded when the necessity for environmental remediation or other potential environmental liabilities becomes probable and the costs can be reasonably estimated. Accruals for estimated losses from environmental remediation obligations are recognized no later than at the time of the completion of the remediation feasibility study. These accruals are adjusted as additional information becomes available or as circumstances change. Costs of future expenditures for environmental-remediation obligations are not discounted to their present value. See Note 14.

Segments policy

Segments. Because WGP reflects its ownership interest in WES on a consolidated basis, and has no independent operations or material assets outside those of WES, WGP’s segment analysis and presentation is the same as that of WES. WES’s operations are organized into a single operating segment, the assets of which gather, process, compress, treat and transport Anadarko and third-party natural gas, condensate, NGLs and crude oil in the United States.

Revenues and cost of product policy

Revenues and cost of product. Under its fee-based gathering, treating and processing arrangements, WES is paid a fixed fee based on the volume and thermal content of natural gas and recognizes revenues for its services in the month such services are performed. Producers’ wells are connected to WES’s gathering systems for delivery of natural gas to WES’s processing or treating plants, where the natural gas is processed to extract NGLs and condensate or treated in order to satisfy pipeline specifications. In some areas, where no processing is required, the producers’ gas is gathered and delivered to pipelines for market delivery. Under cost-of-service gathering agreements, fees are earned for gathering and compression services based on rates calculated in a cost-of-service model and reviewed periodically over the life of the agreements. Under percent-of-proceeds contracts, revenue is recognized when the natural gas, NGLs or condensate are sold. The percentage of the product sale ultimately paid to the producer is recorded as a related cost of product expense.

WES purchases natural gas volumes at the wellhead for gathering and processing. As a result, WES has volumes of NGLs and condensate to sell and volumes of residue to either sell, to use for system fuel or to satisfy keep-whole obligations. In addition, depending upon specific contract terms, condensate and NGLs recovered during gathering and processing are either returned to the producer or retained and sold. Under keep-whole contracts, when condensate or NGLs are retained and sold, producers are kept whole for the condensate or NGL volumes through the receipt of a thermally equivalent volume of residue. The keep-whole contract conveys an economic benefit to WES when the combined value of the individual NGLs is greater in the form of liquids than as a component of the natural gas stream; however, WES is adversely impacted when the value of the NGLs is lower than the value of the natural gas stream including the liquids. WES has commodity price swap agreements with Anadarko to mitigate exposure to a substantial majority of the commodity price uncertainty that would otherwise be present as a result of the purchase and sale of natural gas, condensate or NGLs. See Note 5. Revenue is recognized from the sale of condensate and NGLs upon transfer of title and related purchases are recorded as cost of product.

WES earns transportation revenues through firm contracts that obligate each of its customers to pay a monthly reservation or demand charge regardless of the pipeline capacity used by that customer. An additional commodity usage fee is charged to the customer based on the actual volume of natural gas transported. Transportation revenues are also generated from interruptible contracts pursuant to which a fee is charged to the customer based on volumes transported through the pipeline. Revenues for transportation of natural gas and NGLs are recognized over the period of firm transportation contracts or, in the case of usage fees and interruptible contracts, when the volumes are received into the pipeline. From time to time, certain revenues may be subject to refund pending the outcome of rate matters before the Federal Energy Regulatory Commission (the “FERC”) and reserves are established where appropriate.

Proceeds from the sale of residue, NGLs and condensate are reported as revenues from natural gas, natural gas liquids and condensate sales in the consolidated statements of income. Revenues attributable to the fixed-fee component of gathering and processing contracts as well as demand charges and commodity usage fees on transportation contracts are reported as revenues from gathering, processing and transportation of natural gas and natural gas liquids in the consolidated statements of income.

Equity-based compensation policy

Equity-based compensation. Concurrently with WGP’s IPO, WGP GP adopted the Western Gas Equity Partners, LP 2012 Long-Term Incentive Plan (the “WGP LTIP”). The WGP LTIP permits the issuance of up to 3,000,000 WGP common units, of which 2,959,364 units remained available for future issuance as of December 31, 2014. Upon vesting of each phantom unit, the holder will receive common units of WGP or, at the discretion of WGP GP’s Board of Directors, cash in an amount equal to the market value of common units of WGP on the vesting date. Equity-based compensation expense attributable to grants made under the WGP LTIP impacts cash flows from operating activities only to the extent cash payments are made to a participant in lieu of issuance of WGP common units to the participant. Stock-based compensation expense attributable to awards granted under the WGP LTIP is amortized over the vesting periods applicable to the awards.

The Western Gas Partners, LP 2008 Long-Term Incentive Plan (the “WES LTIP”) was adopted by WES GP concurrently with the IPO of WES and permits the issuance of up to 2,250,000 WES common units, of which 2,133,227 units remained available for future issuance as of December 31, 2014. Upon vesting of each phantom unit award, the holder will receive common units of WES or, at the discretion of WES GP’s Board of Directors, cash in an amount equal to the market value of common units of WES on the vesting date. Equity-based compensation expense attributable to grants made under the WES LTIP impact cash flows from operating activities only to the extent cash payments are made to a participant in lieu of issuance of common units to the participant. Stock-based compensation expense attributable to awards granted under the WES LTIP is amortized over the vesting periods applicable to the awards.

Additionally, general and administrative expenses include equity-based compensation costs allocated by Anadarko for grants made pursuant to (i) the Western Gas Holdings, LLC Equity Incentive Plan, as amended and restated (the “Incentive Plan”) for the year ended December 31, 2012 and (ii) the Anadarko Petroleum Corporation 1999 Stock Incentive Plan and the Anadarko Petroleum Corporation 2008 and 2012 Omnibus Incentive Compensation Plans (Anadarko’s plans are referred to collectively as the “Anadarko Incentive Plans”) for all periods presented. Grants made under equity-based compensation plans result in equity-based compensation expense, which is determined by reference to the fair value of equity compensation. For equity-based awards ultimately settled through the issuance of units or stock, the fair value is measured as of the date of the relevant equity grant. Equity-based compensation granted under the Anadarko Incentive Plans does not impact cash flows from operating activities since the offset to compensation expense is recorded as a contribution to partners’ capital in the consolidated financial statements at the time of contribution, when the expense is realized. However, distribution equivalent rights awarded in tandem with equity-or liability-based awards are paid in cash and reflected within financing cash flows in the consolidated statements of cash flows. See Note 6.

Income taxes policy

WES income taxes. WES generally is not subject to federal income tax or state income tax other than Texas margin tax on the portion of its income that is apportionable to Texas. Deferred state income taxes are recorded on temporary differences between the financial statement carrying amounts of assets and liabilities and their respective tax bases. WES routinely assesses the realizability of its deferred tax assets. If WES concludes that it is more likely than not that some of the deferred tax assets will not be realized, the tax asset is reduced by a valuation allowance. Federal and state current and deferred income tax expense was recorded on WES assets prior to WES’s acquisition of these assets from Anadarko.

For periods beginning on and subsequent to WES’s acquisition of the WES assets, WES makes payments to Anadarko pursuant to the tax sharing agreement entered into between Anadarko and WES for its estimated share of taxes from all forms of taxation, excluding taxes imposed by the United States, that are included in any combined or consolidated returns filed by Anadarko. The aggregate difference in the basis of WES’s assets for financial and tax reporting purposes cannot be readily determined as WES does not have access to information about each partner’s tax attributes in WES.

The accounting standards for uncertain tax positions defines the criteria an individual tax position must satisfy for any part of the benefit of that position to be recognized in the financial statements. WES had no material uncertain tax positions at December 31, 2014 or 2013.

With respect to assets acquired from Anadarko, WES recorded Anadarko’s historic current and deferred income taxes for the periods prior to WES’s ownership of the assets. For periods subsequent to WES’s acquisition, WES is not subject to tax except for the Texas margin tax and, accordingly, does not record current and deferred federal income taxes related to the assets acquired from Anadarko.

WGP income taxes. Prior to its September 2012 conversion from a limited liability company to a limited partnership, WGP was WGR Holdings, LLC, a single-member Delaware limited liability company treated as a division of Anadarko and disregarded for U.S. federal income tax purposes. As such, WGR Holdings, LLC was included in Anadarko’s consolidated income tax return for federal and state income tax purposes. In addition to WES’s historic Texas margin tax expense and liabilities, the accompanying consolidated financial statements of WGP include income tax expense and liabilities incurred by WGR Holdings, LLC, computed on a separate-return basis.

Deferred federal and state income taxes included in the accompanying consolidated financial statements are attributable to temporary differences between the financial statement carrying amount and tax basis of WGP’s investment in WES. WGP’s accounting policy is to “look through” its investment in WES for purposes of calculating deferred income tax asset and liability balances attributable to WGP’s interests in WES. The application of such accounting policy resulted in no deferred income taxes being recognized for the book and tax basis difference in goodwill, which is non-deductible for tax purposes for all periods presented. WGP had no material uncertain tax positions at December 31, 2014 or 2013.

Net income per common unit policy

Net income per common unit. Earnings per unit is calculated by dividing the limited partners’ interest in net income by the weighted-average number of common units outstanding. Net income per common unit is calculated assuming that cash distributions are equal to the net income attributable to WGP. Net income attributable to periods prior to WGP’s IPO is not allocated to the limited partners for purposes of calculating net income per unit. As a result, pre-IPO net income, representing the financial results prior to WGP’s IPO on December 12, 2012, has been excluded from the limited partners’ interest in net income. Net income equal to the amount of available cash (as defined in WGP’s partnership agreement) is allocated to the common unitholders consistent with actual cash distributions. See Note 4.

Recently issued accounting standards policy

Recently issued accounting standards. Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers, supersedes the revenue recognition requirements in Topic 605, Revenue Recognition, and industry-specific guidance in Subtopic 932-605, Extractive Activities—Oil and Gas—Revenue Recognition, and requires an entity to recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This ASU is effective for annual and interim periods beginning in 2017 and is required to be adopted using one of two retrospective application methods, with no early adoption permitted. WGP is currently evaluating the impact of the adoption of this ASU on its consolidated financial statements.

ASU 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity, changes the criteria for reporting discontinued operations and requires additional disclosures, both for discontinued operations and for individually significant dispositions and assets classified as held for sale not qualifying as discontinued operations. This ASU is effective for annual and interim periods beginning in 2015, with early adoption permitted for disposals or for assets classified as held for sale that have not been reported in previously issued financial statements. WGP early adopted this ASU on a prospective basis beginning with the first quarter of 2014. The adoption did not have a material impact on WGP’s consolidated financial statements.

ASU 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists, requires that an unrecognized tax benefit, or a portion of an unrecognized tax benefit, be presented in the financial statements as a reduction to a deferred tax asset, except in certain circumstances. This ASU is effective for annual and interim periods beginning in 2014. WGP adopted this ASU on a prospective basis beginning with the first quarter of 2014. The adoption did not have a material impact on WGP’s consolidated financial statements. See Note 7—Income Taxes.

Equity investments policy

Management evaluates its equity investments for impairment whenever events or changes in circumstances indicate that the carrying value of such investments may have experienced a decline in value that is other than temporary. When evidence of loss in value has occurred, management compares the estimated fair value of the investment to the carrying value of the investment to determine whether the investment has been impaired. Management assesses the fair value of equity investments using commonly accepted techniques, and may use more than one method, including, but not limited to, recent third-party comparable sales and discounted cash flow models. If the estimated fair value is less than the carrying value, the excess of the carrying value over the estimated fair value is recognized as an impairment loss.