Commitments and Contingencies	3 Months Ended
Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 15 - Commitments and Contingencies In addition to the matters discussed below, MasTec is subject to a variety of legal cases, claims and other disputes that arise from time to time in the ordinary course of its business. MasTec cannot provide assurance that it will be successful in recovering all or any of the potential damages it has claimed or in defending claims against it. The outcome of such cases, claims and disputes, including those set forth below, cannot be predicted with certainty and an unfavorable resolution of one or more of them could have a material adverse effect on the Company’s business, financial condition, results of operations and cash flows. PPL. In October 2012, PPL Electric Utilities Corporation (“PPL”) and T&D Power, Inc., a MasTec, Inc. subsidiary (“T&D”), entered into a $206 million overhead transmission line construction contract (the “Contract”), pursuant to which T&D agreed to construct an approximately 100-mile transmission line in Pennsylvania. In September 2013, PPL issued a notice terminating the Contract for convenience. T&D then submitted termination invoices to recover certain pre-termination costs, overhead and profit, as well as termination-related demobilization costs, along with the applicable overhead and profit. PPL disputes these invoices. As a result of the dispute, T&D sued PPL in December 2013 in federal court in the Eastern District of Pennsylvania, and is pursuing claims in excess of $40 million for breach of contract, including PPL’s breach of its implied duty of good faith and fair dealing. Although T&D has attempted to resolve the dispute with PPL through negotiation, mediation in 2014 was unsuccessful. Discovery has been completed. In July 2015, PPL filed a motion for partial summary judgment, and T&D filed a response. A trial is scheduled for October 2015. SunLight Entities. In 2011, Power Partners MasTec, LLC., a MasTec, Inc. subsidiary (“Power Partners”), entered into engineering, procurement, and construction agreements (the “EPC Agreements”) with special purpose entities, SunLight General Somerset Solar, LLC, SunLight General Morris Solar, LLC and SunLight General Sussex Solar, LLC (collectively, the “SunLight Entities”), respectively, to perform design and construction services for three public solar projects in New Jersey located in Somerset, Morris and Sussex Counties (the “Projects”). Power Partners and the SunLight Entities engaged in three separate arbitration proceedings against each other to address various disputes that existed between the parties regarding the Projects. In August 2014, the arbitration panel rendered awards in Power Partners’ favor in the aggregate amount of approximately $68 million, including fees and expenses. Power Partners also filed a lawsuit in June 2013 in federal court in New Jersey against the Somerset and Morris Authorities (the “Authorities”) and the principals of the SunLight Entities with claims exceeding $60 million as part of its efforts to seek payment of amounts that were also the subject of the arbitration proceedings. In March 2015, the Authorities, the SunLight Entities and principals and Power Partners entered into separate settlement agreements. As part of the settlement, Power Partners has received amounts that are substantially equal to the previously recorded amounts, and all of the parties executed mutual releases. Wrigley v. MasTec, Inc. On May 7, 2015, a putative class action lawsuit (the “Lawsuit”), Wrigley v. MasTec, Inc., et. al. (Case No. 1:15-cv-21740) was filed in the United States District Court, Southern District of Florida, naming the Company, the Company’s Chief Executive Officer, José R. Mas, and the Company’s Chief Financial Officer, George L. Pita, as defendants. The Lawsuit has been purportedly brought by a shareholder, both individually and on behalf of a putative class of shareholders, alleging violations of the federal securities laws arising from alleged false or misleading statements contained in, or alleged material omissions from, certain of the Company’s filings with the SEC and other statements, in each case with respect to accounting matters that are the subject of the independent internal investigation being conducted by the Audit Committee of the Company’s Board of Directors. The Lawsuit seeks damages, prejudgment and post-judgment interest, as well as reasonable attorneys’ fees, expert fees and other costs. The Company believes that the Lawsuit is without merit and intends to vigorously defend against it; however, there can be no assurance that the Company will be successful in its defense. Other Commitments and Contingencies Regulatory Matters. The Company has self-reported to the staff of the SEC (“the Staff”) regarding the previously disclosed Audit Committee’s independent investigation and is cooperating with the Staff’s requests for additional information regarding the investigation. The Company intends to continue full cooperation with the SEC. Leases. In the ordinary course of business, the Company enters into non-cancelable operating leases for certain of its facility, vehicle and equipment needs, including related party leases. See Note 9 - Lease Obligations. Letters of Credit. In the ordinary course of business, the Company is required to post letters of credit for its insurance carriers, surety bond providers and in support of performance under certain contracts. Such letters of credit are generally issued by a bank or similar financial institution. The letter of credit commits the issuer to pay specified amounts to the holder of the letter of credit under certain conditions. If this were to occur, the Company would be required to reimburse the issuer of the letter of credit, which, depending upon the circumstances, could result in a charge to earnings. As of March 31, 2015 and December 31, 2014, there were $153.2 million and $153.6 million, respectively, of letters of credit issued under the Company’s Credit Facility. The Company is not aware of material claims relating to outstanding letters of credit as of March 31, 2015 or December 31, 2014. Performance and Payment Bonds. In the ordinary course of business, MasTec is required by certain customers to provide performance and payment bonds for some of the Company’s contractual commitments related to projects in process. These bonds provide a guarantee to the customer that the Company will perform under the terms of a contract and that the Company will pay subcontractors and vendors. If the Company fails to perform under a contract or to pay subcontractors and vendors, the customer may demand that the surety make payments or provide services under the bond. The Company must reimburse the surety for expenses or outlays it incurs. As of March 31, 2015, the estimated cost to complete projects secured by the Company’s $665.6 million in performance and payment bonds was $51.6 million. As of December 31, 2014, the estimated cost to complete projects secured by the Company’s $748.3 million in performance and payment bonds was $60.1 million. These amounts do not include performance and payment bonds associated with the Company’s equity method investments and contractual joint venture, which are separately disclosed in Note 3 - Acquisitions. Investments in Affiliates and Other Entities. The Company holds an undivided interest in a contractual joint venture with a third party for the purpose of providing infrastructure construction services under certain customer contracts. Losses incurred by the joint venture are generally shared proportionally by the joint venture members, with members of the joint venture jointly and severally liable for all of the obligations of the joint venture. The joint venture agreement provides that each joint venturer indemnify the other party for any liabilities incurred by such joint venture in excess of its ratable portion of such liabilities. Thus, it is possible that the Company could be required to pay or perform obligations in excess of its share if the other joint venturer fails or refuses to pay or perform its share of the obligations. As of March 31, 2015, the Company was not aware of circumstances that would reasonably lead to future claims against it for material amounts. From time to time, the Company may provide financing to its unconsolidated affiliates, including its equity method investees and/or contractual joint venture. During the first quarter of 2015, excluding receivership commitments related to an equity method investee being wound down, the Company paid approximately $9.6 million under such financing arrangements, and, through August 3, 2015, had paid an additional $6.8 million, none of which additional amount was committed as of March 31, 2015. As of December 31, 2014, there were no amounts committed under such financing arrangements. See Note 3 - Acquisitions for details pertaining to financing commitments related to the Company’s equity method investments and contractual joint venture. Self-Insurance. MasTec maintains insurance policies for workers’ compensation, general liability and automobile liability, which are subject to per claim deductibles. The Company also maintains excess umbrella coverage. As of March 31, 2015 and December 31, 2014, MasTec’s liability for unpaid claims and associated expenses, including incurred but not reported losses related to these policies, totaled $71.2 million and $70.3 million, respectively, of which $43.4 million and $39.6 million, respectively, were reflected within other long-term liabilities in the consolidated balance sheets. MasTec also maintains an insurance policy with respect to employee group medical claims, which is subject to annual per employee maximum losses. MasTec’s liability for employee group medical claims as of March 31, 2015 and December 31, 2014 totaled $4.2 million and $4.4 million, respectively. The Company is required to post letters of credit and provide cash collateral to certain of its insurance carriers and to provide surety bonds in certain states. Insurance-related letters of credit for the Company’s workers’ compensation, general liability and automobile liability policies amounted to $75.0 million as of both March 31, 2015 and December 31, 2014. In addition, cash collateral deposited with insurance carriers, which is included within other long-term assets in the consolidated balance sheets, amounted to $1.4 million and $1.2 million for these policies as of March 31, 2015 and December 31, 2014, respectively. Outstanding surety bonds related to workers’ compensation self-insurance programs amounted to $13.0 million as of both March 31, 2015 and December 31, 2014. Employment Agreements. The Company has employment agreements with certain executives and other employees, which provide for compensation and certain other benefits and for severance payments under certain circumstances. Certain employment agreements also contain clauses that become effective upon a change in control of the Company. Upon the occurrence of any of the defined events in the various employment agreements, the Company would be obligated to pay certain amounts to the relevant employees, which vary with the level of the employees’ respective responsibility. Collective Bargaining Agreements and Multi-Employer Plans. Certain of MasTec’s subsidiaries are party to various collective bargaining agreements with unions representing certain of their employees. These agreements require the subsidiaries party to the agreements to pay specified wages, provide certain benefits to their union employees and contribute certain amounts to multi-employer pension plans and employee benefit trusts. The collective bargaining agreements expire at various times and have typically been renegotiated and renewed on terms similar to the ones contained in the expiring agreements. The Employee Retirement Income Security Act of 1974, as amended by the Multi-Employer Pension Plan Amendments Act of 1980 (collectively, “ERISA”), which governs U.S.-registered multi-employer pension plans, subjects employers to substantial liabilities in the event of the employer’s complete or partial withdrawal from, or upon termination of, such plans. Under current law pertaining to employers who are contributors to U.S.-registered multi-employer defined benefit plans, a plan’s termination, an employer’s voluntary withdrawal from, or the mass withdrawal of contributing employers from, an underfunded multi-employer defined benefit plan requires participating employers to make payments to the plan for their proportionate share of the multi-employer plan’s unfunded vested liabilities. These liabilities include an allocable share of the unfunded vested benefits of the plan for all plan participants, not only for benefits payable to participants of the contributing employer. As a result, participating employers may bear a higher proportion of liability for unfunded vested benefits if the other participating employers cease to contribute to, or withdraw from, the plan. The allocable portion of liability to participating employers could be more disproportionate if employers that have withdrawn from the plan are insolvent, or if they otherwise fail to pay their proportionate share of the withdrawal liability. The Company currently contributes, and in the past has contributed to, plans that are underfunded, and, therefore, could have potential liability associated with a voluntary or involuntary withdrawal from, or termination of, these plans. While the Company does not currently have plans to withdraw from, and is not aware of related liabilities associated with these plans, there can be no assurance that the Company will not be assessed liabilities in the future. The Pension Protection Act of 2006 (“PPA”) added funding rules to U.S.-registered plans classified as “endangered,” “seriously endangered,” or “critical” status. The PPA requires that underfunded pension plans improve their funding ratios within prescribed intervals based on their level of underfunding. If a plan is in critical status, benefit reductions may apply and/or participating employers could be required to make additional contributions. In addition, if a multi-employer defined benefit plan fails to satisfy certain minimum funding requirements, the Internal Revenue Service (“IRS”) may impose on the employers contributing to such plan a non-deductible excise tax of 5% of the amount of the accumulated funding deficiency. Based upon the information available to the Company from plan administrators as of March 31, 2015, several of the multi-employer pension plans in which it participates are underfunded and, as a result, the Company could be required to increase its contributions. Some of the Company’s subsidiaries have also been notified that certain plans to which they contribute are in “critical” status and require additional contributions in the form of a surcharge on future benefit contributions required for future work performed by union employees covered by these plans. The amount of additional funds the Company may be obligated to contribute in the future cannot be estimated, as these amounts are based on future levels of work of the union employees covered by the plans. In November 2014, the Company, along with other members of the Pipe Line Contractors Association (“PLCA”), voluntarily terminated its participation in several defined benefit multi-employer pension plans. No withdrawal liability was assessed as of the date of the Company’s termination of participation in these plans. There can be no assurance, however, that these plans, which were in critical status as of the date the Company terminated its participation, will not assess penalties in the future. Additionally, in November 2011, the Company, along with other members of the PLCA, voluntarily withdrew from the Central States Southeast and Southwest Areas Pension Fund (“Central States”), a defined benefit multi-employer pension plan that is in critical status. In connection with this withdrawal, a $6.4 million withdrawal liability was established based on an estimate provided by the Central States administrator as of the date of withdrawal. The Company began paying installments towards this withdrawal liability in 2013, of which $3.9 million and $4.2 million was outstanding as of March 31, 2015 and December 31, 2014, respectively. The Company withdrew from Central States in order to mitigate its liability in connection with the plan; however, Central States has asserted that the PLCA members did not effectively withdraw in 2011 and are, therefore, responsible for a withdrawal liability that includes 2011 contribution amounts. By letter dated March 14, 2013, Central States demanded $11 million in withdrawal liability from the Company, which included 2011 contribution amounts. The Company is vigorously opposing this demand because it believes that it legally and effectively withdrew from Central States in November 2011. If Central States were to prevail in its assertion that the Company withdrew after that date, then the initial amount of the Company’s withdrawal liability would increase to approximately $11 million. If Central States or other plans from which the Company has withdrawn were to undergo a mass withdrawal, as defined by ERISA and the Pension Benefit Guaranty Corporation, within the three-year period commencing with the beginning of the calendar year during which the Company effectively withdrew from the plan, there could be additional liability. Given the uncertain nature of the outcome of these factors, the ultimate withdrawal liability can only be estimated. Indemnities. The Company generally indemnifies its customers for the services it provides under its contracts, as well as other specified liabilities, which may subject the Company to indemnity claims, liabilities and related litigation. As of March 31, 2015 and December 31, 2014, the Company was not aware of material asserted or unasserted claims in connection with these indemnity obligations. Other Guarantees. In the ordinary course of its business, from time to time, MasTec guarantees the obligations of its subsidiaries, including obligations under certain contracts with customers, certain lease obligations and in some states, obligations in connection with obtaining contractors’ licenses. MasTec has also issued performance and other guarantees in connection with its undivided interest in a contractual joint venture and certain of its equity investees. See Note 3 - Acquisitions. MasTec also generally warrants the work it performs for a one to two year period following substantial completion of a project. MasTec has not historically accrued reserves for potential warranty claims as they have been immaterial. Concentrations of Risk. The Company had approximately 340 customers for the three month period ended March 31, 2015. As of March 31, 2015, one customer accounted for approximately 11% of the Company’s consolidated net accounts receivable position, which represents accounts receivable, net, less billings in excess of costs and earnings. As of December 31, 2014, one customer accounted for 18% of the Company’s consolidated net accounts receivable position. For the three month periods ended March 31, 2015 and 2014, the Company derived 58% and 71% respectively, of revenues from its top ten customers. Taking into consideration the July 2015 acquisition of DIRECTV^® by AT&T, revenue derived from the Company’s ten largest customers would have totaled 60% and 73%, respectively, for three month periods ended March 31, 2015 and 2014. In addition, as of March 31, 2015 and December 31, 2014, a single customer would have represented 12% and 19%, respectively, of the Company’s consolidated net accounts receivable position. See Note 14 - Segments and Related Information for significant customer revenue concentration information.

Note 15 - Commitments and Contingencies

In addition to the matters discussed below, MasTec is subject to a variety of legal cases, claims and other disputes that arise from time to time in the ordinary course of its business. MasTec cannot provide assurance that it will be successful in recovering all or any of the potential damages it has claimed or in defending claims against it. The outcome of such cases, claims and disputes, including those set forth below, cannot be predicted with certainty and an unfavorable resolution of one or more of them could have a material adverse effect on the Company’s business, financial condition, results of operations and cash flows.

PPL. In October 2012, PPL Electric Utilities Corporation (“PPL”) and T&D Power, Inc., a MasTec, Inc. subsidiary (“T&D”), entered into a $206 million overhead transmission line construction contract (the “Contract”), pursuant to which T&D agreed to construct an approximately 100-mile transmission line in Pennsylvania. In September 2013, PPL issued a notice terminating the Contract for convenience. T&D then submitted termination invoices to recover certain pre-termination costs, overhead and profit, as well as termination-related demobilization costs, along with the applicable overhead and profit. PPL disputes these invoices. As a result of the dispute, T&D sued PPL in December 2013 in federal court in the Eastern District of Pennsylvania, and is pursuing claims in excess of $40 million for breach of contract, including PPL’s breach of its implied duty of good faith and fair dealing. Although T&D has attempted to resolve the dispute with PPL through negotiation, mediation in 2014 was unsuccessful. Discovery has been completed. In July 2015, PPL filed a motion for partial summary judgment, and T&D filed a response. A trial is scheduled for October 2015.

SunLight Entities. In 2011, Power Partners MasTec, LLC., a MasTec, Inc. subsidiary (“Power Partners”), entered into engineering, procurement, and construction agreements (the “EPC Agreements”) with special purpose entities, SunLight General Somerset Solar, LLC, SunLight General Morris Solar, LLC and SunLight General Sussex Solar, LLC (collectively, the “SunLight Entities”), respectively, to perform design and construction services for three public solar projects in New Jersey located in Somerset, Morris and Sussex Counties (the “Projects”). Power Partners and the SunLight Entities engaged in three separate arbitration proceedings against each other to address various disputes that existed between the parties regarding the Projects. In August 2014, the arbitration panel rendered awards in Power Partners’ favor in the aggregate amount of approximately $68 million, including fees and expenses. Power Partners also filed a lawsuit in June 2013 in federal court in New Jersey against the Somerset and Morris Authorities (the “Authorities”) and the principals of the SunLight Entities with claims exceeding $60 million as part of its efforts to seek payment of amounts that were also the subject of the arbitration proceedings.

In March 2015, the Authorities, the SunLight Entities and principals and Power Partners entered into separate settlement agreements. As part of the settlement, Power Partners has received amounts that are substantially equal to the previously recorded amounts, and all of the parties executed mutual releases.

Wrigley v. MasTec, Inc. On May 7, 2015, a putative class action lawsuit (the “Lawsuit”), Wrigley v. MasTec, Inc., et. al. (Case No. 1:15-cv-21740) was filed in the United States District Court, Southern District of Florida, naming the Company, the Company’s Chief Executive Officer, José R. Mas, and the Company’s Chief Financial Officer, George L. Pita, as defendants. The Lawsuit has been purportedly brought by a shareholder, both individually and on behalf of a putative class of shareholders, alleging violations of the federal securities laws arising from alleged false or misleading statements contained in, or alleged material omissions from, certain of the Company’s filings with the SEC and other statements, in each case with respect to accounting matters that are the subject of the independent internal investigation being conducted by the Audit Committee of the Company’s Board of Directors. The Lawsuit seeks damages, prejudgment and post-judgment interest, as well as reasonable attorneys’ fees, expert fees and other costs. The Company believes that the Lawsuit is without merit and intends to vigorously defend against it; however, there can be no assurance that the Company will be successful in its defense.

Other Commitments and Contingencies

Regulatory Matters. The Company has self-reported to the staff of the SEC (“the Staff”) regarding the previously disclosed Audit Committee’s independent investigation and is cooperating with the Staff’s requests for additional information regarding the investigation. The Company intends to continue full cooperation with the SEC.

Leases. In the ordinary course of business, the Company enters into non-cancelable operating leases for certain of its facility, vehicle and equipment needs, including related party leases. See Note 9 - Lease Obligations.

Letters of Credit. In the ordinary course of business, the Company is required to post letters of credit for its insurance carriers, surety bond providers and in support of performance under certain contracts. Such letters of credit are generally issued by a bank or similar financial institution. The letter of credit commits the issuer to pay specified amounts to the holder of the letter of credit under certain conditions. If this were to occur, the Company would be required to reimburse the issuer of the letter of credit, which, depending upon the circumstances, could result in a charge to earnings. As of March 31, 2015 and December 31, 2014, there were $153.2 million and $153.6 million, respectively, of letters of credit issued under the Company’s Credit Facility. The Company is not aware of material claims relating to outstanding letters of credit as of March 31, 2015 or December 31, 2014.

Performance and Payment Bonds. In the ordinary course of business, MasTec is required by certain customers to provide performance and payment bonds for some of the Company’s contractual commitments related to projects in process. These bonds provide a guarantee to the customer that the Company will perform under the terms of a contract and that the Company will pay subcontractors and vendors. If the Company fails to perform under a contract or to pay subcontractors and vendors, the customer may demand that the surety make payments or provide services under the bond. The Company must reimburse the surety for expenses or outlays it incurs. As of March 31, 2015, the estimated cost to complete projects secured by the Company’s $665.6 million in performance and payment bonds was $51.6 million. As of December 31, 2014, the estimated cost to complete projects secured by the Company’s $748.3 million in performance and payment bonds was $60.1 million. These amounts do not include performance and payment bonds associated with the Company’s equity method investments and contractual joint venture, which are separately disclosed in Note 3 - Acquisitions.

Investments in Affiliates and Other Entities. The Company holds an undivided interest in a contractual joint venture with a third party for the purpose of providing infrastructure construction services under certain customer contracts. Losses incurred by the joint venture are generally shared proportionally by the joint venture members, with members of the joint venture jointly and severally liable for all of the obligations of the joint venture. The joint venture agreement provides that each joint venturer indemnify the other party for any liabilities incurred by such joint venture in excess of its ratable portion of such liabilities. Thus, it is possible that the Company could be required to pay or perform obligations in excess of its share if the other joint venturer fails or refuses to pay or perform its share of the obligations. As of March 31, 2015, the Company was not aware of circumstances that would reasonably lead to future claims against it for material amounts. From time to time, the Company may provide financing to its unconsolidated affiliates, including its equity method investees and/or contractual joint venture. During the first quarter of 2015, excluding receivership commitments related to an equity method investee being wound down, the Company paid approximately $9.6 million under such financing arrangements, and, through August 3, 2015, had paid an additional $6.8 million, none of which additional amount was committed as of March 31, 2015. As of December 31, 2014, there were no amounts committed under such financing arrangements. See Note 3 - Acquisitions for details pertaining to financing commitments related to the Company’s equity method investments and contractual joint venture.

Self-Insurance. MasTec maintains insurance policies for workers’ compensation, general liability and automobile liability, which are subject to per claim deductibles. The Company also maintains excess umbrella coverage. As of March 31, 2015 and December 31, 2014, MasTec’s liability for unpaid claims and associated expenses, including incurred but not reported losses related to these policies, totaled $71.2 million and $70.3 million, respectively, of which $43.4 million and $39.6 million, respectively, were reflected within other long-term liabilities in the consolidated balance sheets. MasTec also maintains an insurance policy with respect to employee group medical claims, which is subject to annual per employee maximum losses. MasTec’s liability for employee group medical claims as of March 31, 2015 and December 31, 2014 totaled $4.2 million and $4.4 million, respectively.

The Company is required to post letters of credit and provide cash collateral to certain of its insurance carriers and to provide surety bonds in certain states. Insurance-related letters of credit for the Company’s workers’ compensation, general liability and automobile liability policies amounted to $75.0 million as of both March 31, 2015 and December 31, 2014. In addition, cash collateral deposited with insurance carriers, which is included within other long-term assets in the consolidated balance sheets, amounted to $1.4 million and $1.2 million for these policies as of March 31, 2015 and December 31, 2014, respectively. Outstanding surety bonds related to workers’ compensation self-insurance programs amounted to $13.0 million as of both March 31, 2015 and December 31, 2014.

Employment Agreements. The Company has employment agreements with certain executives and other employees, which provide for compensation and certain other benefits and for severance payments under certain circumstances. Certain employment agreements also contain clauses that become effective upon a change in control of the Company. Upon the occurrence of any of the defined events in the various employment agreements, the Company would be obligated to pay certain amounts to the relevant employees, which vary with the level of the employees’ respective responsibility.

Collective Bargaining Agreements and Multi-Employer Plans. Certain of MasTec’s subsidiaries are party to various collective bargaining agreements with unions representing certain of their employees. These agreements require the subsidiaries party to the agreements to pay specified wages, provide certain benefits to their union employees and contribute certain amounts to multi-employer pension plans and employee benefit trusts. The collective bargaining agreements expire at various times and have typically been renegotiated and renewed on terms similar to the ones contained in the expiring agreements.

The Employee Retirement Income Security Act of 1974, as amended by the Multi-Employer Pension Plan Amendments Act of 1980 (collectively, “ERISA”), which governs U.S.-registered multi-employer pension plans, subjects employers to substantial liabilities in the event of the employer’s complete or partial withdrawal from, or upon termination of, such plans. Under current law pertaining to employers who are contributors to U.S.-registered multi-employer defined benefit plans, a plan’s termination, an employer’s voluntary withdrawal from, or the mass withdrawal of contributing employers from, an underfunded multi-employer defined benefit plan requires participating employers to make payments to the plan for their proportionate share of the multi-employer plan’s unfunded vested liabilities. These liabilities include an allocable share of the unfunded vested benefits of the plan for all plan participants, not only for benefits payable to participants of the contributing employer. As a result, participating employers may bear a higher proportion of liability for unfunded vested benefits if the other participating employers cease to contribute to, or withdraw from, the plan. The allocable portion of liability to participating employers could be more disproportionate if employers that have withdrawn from the plan are insolvent, or if they otherwise fail to pay their proportionate share of the withdrawal liability. The Company currently contributes, and in the past has contributed to, plans that are underfunded, and, therefore, could have potential liability associated with a voluntary or involuntary withdrawal from, or termination of, these plans. While the Company does not currently have plans to withdraw from, and is not aware of related liabilities associated with these plans, there can be no assurance that the Company will not be assessed liabilities in the future. The Pension Protection Act of 2006 (“PPA”) added funding rules to U.S.-registered plans classified as “endangered,” “seriously endangered,” or “critical” status. The PPA requires that underfunded pension plans improve their funding ratios within prescribed intervals based on their level of underfunding. If a plan is in critical status, benefit reductions may apply and/or participating employers could be required to make additional contributions. In addition, if a multi-employer defined benefit plan fails to satisfy certain minimum funding requirements, the Internal Revenue Service (“IRS”) may impose on the employers contributing to such plan a non-deductible excise tax of 5% of the amount of the accumulated funding deficiency.

Based upon the information available to the Company from plan administrators as of March 31, 2015, several of the multi-employer pension plans in which it participates are underfunded and, as a result, the Company could be required to increase its contributions. Some of the Company’s subsidiaries have also been notified that certain plans to which they contribute are in “critical” status and require additional contributions in the form of a surcharge on future benefit contributions required for future work performed by union employees covered by these plans. The amount of additional funds the Company may be obligated to contribute in the future cannot be estimated, as these amounts are based on future levels of work of the union employees covered by the plans.

In November 2014, the Company, along with other members of the Pipe Line Contractors Association (“PLCA”), voluntarily terminated its participation in several defined benefit multi-employer pension plans. No withdrawal liability was assessed as of the date of the Company’s termination of participation in these plans. There can be no assurance, however, that these plans, which were in critical status as of the date the Company terminated its participation, will not assess penalties in the future. Additionally, in November 2011, the Company, along with other members of the PLCA, voluntarily withdrew from the Central States Southeast and Southwest Areas Pension Fund (“Central States”), a defined benefit multi-employer pension plan that is in critical status. In connection with this withdrawal, a $6.4 million withdrawal liability was established based on an estimate provided by the Central States administrator as of the date of withdrawal. The Company began paying installments towards this withdrawal liability in 2013, of which $3.9 million and $4.2 million was outstanding as of March 31, 2015 and December 31, 2014, respectively. The Company withdrew from Central States in order to mitigate its liability in connection with the plan; however, Central States has asserted that the PLCA members did not effectively withdraw in 2011 and are, therefore, responsible for a withdrawal liability that includes 2011 contribution amounts. By letter dated March 14, 2013, Central States demanded $11 million in withdrawal liability from the Company, which included 2011 contribution amounts. The Company is vigorously opposing this demand because it believes that it legally and effectively withdrew from Central States in November 2011. If Central States were to prevail in its assertion that the Company withdrew after that date, then the initial amount of the Company’s withdrawal liability would increase to approximately $11 million. If Central States or other plans from which the Company has withdrawn were to undergo a mass withdrawal, as defined by ERISA and the Pension Benefit Guaranty Corporation, within the three-year period commencing with the beginning of the calendar year during which the Company effectively withdrew from the plan, there could be additional liability. Given the uncertain nature of the outcome of these factors, the ultimate withdrawal liability can only be estimated.

Indemnities. The Company generally indemnifies its customers for the services it provides under its contracts, as well as other specified liabilities, which may subject the Company to indemnity claims, liabilities and related litigation. As of March 31, 2015 and December 31, 2014, the Company was not aware of material asserted or unasserted claims in connection with these indemnity obligations.

Other Guarantees. In the ordinary course of its business, from time to time, MasTec guarantees the obligations of its subsidiaries, including obligations under certain contracts with customers, certain lease obligations and in some states, obligations in connection with obtaining contractors’ licenses. MasTec has also issued performance and other guarantees in connection with its undivided interest in a contractual joint venture and certain of its equity investees. See Note 3 - Acquisitions. MasTec also generally warrants the work it performs for a one to two year period following substantial completion of a project. MasTec has not historically accrued reserves for potential warranty claims as they have been immaterial.

Concentrations of Risk. The Company had approximately 340 customers for the three month period ended March 31, 2015. As of March 31, 2015, one customer accounted for approximately 11% of the Company’s consolidated net accounts receivable position, which represents accounts receivable, net, less billings in excess of costs and earnings. As of December 31, 2014, one customer accounted for 18% of the Company’s consolidated net accounts receivable position. For the three month periods ended March 31, 2015 and 2014, the Company derived 58% and 71% respectively, of revenues from its top ten customers. Taking into consideration the July 2015 acquisition of DIRECTV^® by AT&T, revenue derived from the Company’s ten largest customers would have totaled 60% and 73%, respectively, for three month periods ended March 31, 2015 and 2014. In addition, as of March 31, 2015 and December 31, 2014, a single customer would have represented 12% and 19%, respectively, of the Company’s consolidated net accounts receivable position. See Note 14 - Segments and Related Information for significant customer revenue concentration information.