Fair Value of Financial Instruments	9 Months Ended
Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Note 4 – Fair Value of Financial Instruments The Company’s financial instruments include cash and cash equivalents, accounts and notes receivable, equity investments, life insurance assets, cash collateral deposited with insurance carriers, deferred compensation plan assets and liabilities, accounts payable and other current liabilities, acquisition-related contingent consideration and debt obligations. Fair value is the price that would be received to sell an asset or the amount paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The fair value guidance establishes a valuation hierarchy, which requires maximizing the use of observable inputs when measuring fair value. The three levels of inputs that may be used are: (i) Level 1 - quoted market prices in active markets for identical assets or liabilities; (ii) Level 2 - observable market-based inputs or other observable inputs; and (iii) Level 3 - significant unobservable inputs that cannot be corroborated by observable market data, which are generally determined using valuation models incorporating management estimates of market participant assumptions. In instances in which the inputs used to measure fair value fall into different levels of the fair value hierarchy, the fair value measurement classification is determined based on the lowest level input that is significant to the fair value measurement in its entirety. Management’s assessment of the significance of a particular item to the fair value measurement in its entirety requires judgment, including the consideration of inputs specific to the asset or liability. Fair values of financial instruments are estimated using public market prices, quotes from financial institutions and other available information. Due to their short-term maturity, the carrying amounts of cash and cash equivalents, accounts receivable, accounts payable and other current liabilities approximate their fair values. Management believes the carrying values of notes and other receivables, cash collateral deposited with insurance carriers and outstanding balances on its credit facilities approximate their fair values. Acquisition-Related Contingent Consideration Acquisition-related contingent consideration, or “earn-out” liabilities, represent the estimated fair value of future amounts payable for acquisitions of businesses and other interests. Acquisition-related contingent consideration is based on management estimates and entity-specific assumptions, which are Level 3 inputs, and are evaluated on an ongoing basis. As of September 30, 2018 and December 31, 2017, the estimated fair value of the Company’s earn-out liabilities totaled $110.1 million and $117.2 million, respectively, of which $27.5 million and $22.6 million, respectively, was included within other current liabilities. The fair value of the Company’s earn-out liabilities is estimated using income approaches such as discounted cash flows or option pricing models and incorporates significant inputs not observable in the market. Key assumptions include the discount rate and probability-weighted EBITDA projections. Significant changes in any of these assumptions could result in a significantly higher or lower potential earn-out liability. As of September 30, 2018, the range of potential undiscounted earn-out liabilities was estimated to be between $23 million and $173 million; however, there is no maximum payment amount. Acquisition-related contingent consideration activity consists primarily of additions from new business combinations and acquisitions of other interests; payments; and changes in the expected fair value of future earn-out obligations. Fair value adjustments for earn-out liabilities that relate to circumstances that developed after the date of acquisition are recorded within other income or expense, as appropriate. Fair value adjustments for earn-out liabilities that relate to new information obtained about the facts and circumstances that existed as of the date of acquisition, which are referred to as measurement period adjustments, are recorded to goodwill. There were no additions to acquisition-related contingent consideration from new business combinations for the three month period ended September 30, 2018, and additions for the nine month period ended September 30, 2018 totaled approximately $1.5 million. For the three and nine month periods ended September 30, 2017, additions to acquisition-related contingent consideration from new business combinations totaled approximately $64.6 million and $89.6 million, respectively. For the three month period ended September 30, 2018, measurement period adjustments related to acquisition-related contingent consideration totaled an increase of approximately $2.2 million, and for the nine month period ended September 30, 2018, totaled a net increase of approximately $4.2 million, and related to businesses in the Company’s Oil and Gas and Power Generation and Industrial segments. Fair value adjustments related to acquisition-related contingent consideration, including those related to finalization of completed earn-out arrangements, totaled net increases of approximately $5.9 million and $10.3 million for the three and nine month periods ended September 30, 2018, respectively, primarily for businesses in the Company’s Oil and Gas and Communications segments, and for the three and nine month periods ended September 30, 2017, totaled net decreases of approximately $3.0 million and $11.6 million, respectively, for businesses in the Company’s Communications and Electrical Transmission segments. There were no payments of acquisition-related contingent consideration during the three month periods ended September 30, 2018 or 2017, and payments of acquisition-related contingent consideration during the nine month periods ended September 30, 2018 and 2017 totaled $23.1 million and $18.8 million, respectively. Equity Investments The Company’s equity investments as of September 30, 2018 include: (i) the Company’s 33% equity interests in Trans-Pecos Pipeline, LLC (“TPP”) and Comanche Trail Pipeline, LLC (“CTP,” and together with TPP, the “Waha JVs”), which are accounted for as equity method investments; (ii) a $15 million investment in Cross Country Infrastructure Services, Inc. (“CCI”); (iii) the Company’s interests in certain proportionately consolidated non-controlled contractual joint ventures; (iv) the Company’s equity interests in Pensare Acquisition Corp. (“Pensare”); and (v) certain other equity investments. See Note 15 - Related Party Transactions for additional information related to certain of the Company’s equity investments. The fair values of the Company’s equity investments are not readily determinable. The Company’s equity investments, other than those that are proportionately consolidated, or those accounted for as equity method investments or under the fair value option, are measured at cost, adjusted for changes from observable market transactions, less impairment (“adjusted cost basis”). The Company evaluates its investments for impairment by considering a variety of factors, including the earnings capacity of the related investments. Realized and unrealized fair market value gains or losses related to the Company’s equity investments are recognized in other income or expense. Fair value measurements for the Company’s equity investments are classified within Level 3 of the fair value hierarchy based on the nature of the fair value inputs. For the nine month period ended September 30, 2018, there were no upward or downward adjustments related to, or impairments of, the Company’s equity investments measured on an adjusted cost basis. The aggregate carrying value of the Company’s equity investments as of September 30, 2018 and December 31, 2017 totaled approximately $197 million and $141 million, respectively, including approximately $18 million of equity investments measured on an adjusted cost basis for both periods. The Waha JVs. The Waha JVs own and operate two pipelines and a header system that transport natural gas to the Mexican border for export, for which operations commenced in the first half of 2017. For both the three month periods ended September 30, 2018 and 2017, the Company made no equity contributions to these joint ventures, and for the nine month periods ended September 30, 2018 and 2017, made equity contributions totaling $24.5 million and $73.3 million, respectively. The Company previously issued letters of credit in connection with its equity commitments in the Waha JVs. As of September 30, 2018, there were no letters of credit remaining, and as of December 31, 2017, $19 million in letters of credit were outstanding. Equity in earnings related to the Company’s proportionate share of income from the Waha JVs, which is included within the Company’s Other segment, totaled approximately $7.7 million and $7.4 million for the three month periods ended September 30, 2018 and 2017, respectively, and totaled $19.1 million and $15.1 million for the nine month periods ended September 30, 2018 and 2017, respectively. Cumulative undistributed earnings from the Waha JVs totaled $25.1 million as of September 30, 2018. For the three and nine month periods ended September 30, 2018, the Company received $3.2 million and $10.9 million, respectively, in distributions of earnings from the Waha JVs, which amounts are included within operating cash flows. The Company’s net investment in the Waha JVs, which differs from its proportionate share of the net assets of the Waha JVs, due primarily to capitalized investment costs, totaled approximately $168 million and $121 million as of September 30, 2018 and December 31, 2017, respectively. Certain subsidiaries of MasTec have provided pipeline construction services to the Waha JVs. Revenue recognized in connection with work performed for the Waha JVs, including intercompany eliminations, totaled $3.6 million and $255.2 million for the three and nine month periods ended September 30, 2017, respectively, and for the three and nine month periods ended September 30, 2018, was de minimis. As of September 30, 2018 and December 31, 2017, related receivables, net of billings in excess of costs and earnings, totaled $0.1 million and $2.8 million, respectively. TPP and CTP are party to separate non-recourse financing facilities, each of which are secured by pledges of the equity interests in the respective entities, as well as a first lien security interest over virtually all of TPP’s and CTP’s assets. The Waha JVs are also party to certain interest rate swaps, which are accounted for as qualifying cash flow hedges. The Company reflects its proportionate share of any unrealized fair market value gains or losses from fluctuations in interest rates associated with these swaps within other comprehensive income or loss, as appropriate. For the three and nine month periods ended September 30, 2018, the Company’s proportionate share of unrecognized unrealized activity on these interest rate swaps was a gain of approximately $4.1 million and $18.1 million, respectively, or $3.1 million and $13.8 million, net of tax, respectively. For the three and nine month periods ended September 30, 2017, the Company’s proportionate share of unrecognized unrealized activity on these interest rate swaps was a gain of approximately $1.3 million and a loss of approximately $2.1 million, respectively, or a gain of $0.8 million and a loss of $1.3 million, net of tax, respectively. Other Investments. During the third quarter of 2017, the Company paid $2.0 million for approximately 4% of the common stock of Pensare and warrants to purchase 2.0 million shares of Pensare common stock, which is a special purpose acquisition company focusing on transactions in the telecommunications industry. José R. Mas, MasTec’s Chief Executive Officer, is a director of Pensare. The shares of common stock purchased by MasTec are not transferable or salable until one year after Pensare successfully completes a business combination transaction, with limited exceptions, as specified in the agreement. The warrants are exercisable at a purchase price of $11.50 per share after Pensare successfully completes a business combination. Both the warrants and shares expire and/or are effectively forfeitable if Pensare does not successfully complete a business combination by February 1, 2019. The shares, which are measured on an adjusted cost basis, and the warrants, which are derivative financial instruments, are included within other long-term assets in the Company’s consolidated financial statements as of September 30, 2018. Due to the nature of the restrictions, the fair value of the shares is not readily determinable, and there were no upward or downward adjustments related to these shares during either of the three or nine month periods ended September 30, 2018. As of September 30, 2018, the warrants approximated their initially recorded fair values, as determined based on observable and unobservable inputs, including market volatility and the rights and obligations of the warrants, which are Level 3 inputs. During the second quarter of 2018, the Company invested $10.0 million for a 38.5% interest in LifeShield, LLC (“LifeShield”), a home security company, which is measured under the fair value option. Management believes that the fair value option provides an accurate reflection of the economic performance of LifeShield and the value of the Company’s equity interest in the business. To determine the fair value of this investment, the Company estimates the fair value of the entity considering both an income approach, based on discounted cash flows, and a market approach, based on market multiples. The resulting fair value estimates are then evaluated to derive a representative fair value estimate of the entity and the Company’s related investment. As of September 30, 2018, the fair value of this investment was determined to approximate its purchase price. In connection with the 2014 acquisition of Pacer Construction Holdings Corporation and its affiliated operating companies (collectively, “Pacer”), the Company acquired an investment, for which the Company now has minimal involvement, that is in the final stages of being liquidated and is being managed by a receiver. The Company regularly reviews this investment for potential changes in expected recovery estimates, and during the nine month period ended September 30, 2018, recorded $0.9 million of expense related to changes in expected recovery estimates, and during the nine month period ended September 30, 2017, recorded $5.8 million of expense. The Company received $5.4 million of proceeds from the receiver during the nine month period ended September 30, 2018, and received $12.1 million of proceeds during the nine month period ended September 30, 2017. The net carrying value of this asset, which is included within other current assets, totaled $3.0 million and $9.6 million as of September 30, 2018 and December 31, 2017, respectively. Senior Notes As of both September 30, 2018 and December 31, 2017, the gross carrying amount of the Company’s 4.875% senior notes due March 15, 2023 (the “4.875% Senior Notes”), which are measured at fair value on a non-recurring basis, totaled $400 million. As of September 30, 2018 and December 31, 2017, the estimated fair value of the 4.875% Senior Notes, based on Level 1 inputs, totaled $401.0 million and $410.0 million, respectively.

Note 4 – Fair Value of Financial Instruments

The Company’s financial instruments include cash and cash equivalents, accounts and notes receivable, equity investments, life insurance assets, cash collateral deposited with insurance carriers, deferred compensation plan assets and liabilities, accounts payable and other current liabilities, acquisition-related contingent consideration and debt obligations.

Fair value is the price that would be received to sell an asset or the amount paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The fair value guidance establishes a valuation hierarchy, which requires maximizing the use of observable inputs when measuring fair value. The three levels of inputs that may be used are: (i) Level 1 - quoted market prices in active markets for identical assets or liabilities; (ii) Level 2 - observable market-based inputs or other observable inputs; and (iii) Level 3 - significant unobservable inputs that cannot be corroborated by observable market data, which are generally determined using valuation models incorporating management estimates of market participant assumptions. In instances in which the inputs used to measure fair value fall into different levels of the fair value hierarchy, the fair value measurement classification is determined based on the lowest level input that is significant to the fair value measurement in its entirety. Management’s assessment of the significance of a particular item to the fair value measurement in its entirety requires judgment, including the consideration of inputs specific to the asset or liability.

Fair values of financial instruments are estimated using public market prices, quotes from financial institutions and other available information. Due to their short-term maturity, the carrying amounts of cash and cash equivalents, accounts receivable, accounts payable and other current liabilities approximate their fair values. Management believes the carrying values of notes and other receivables, cash collateral deposited with insurance carriers and outstanding balances on its credit facilities approximate their fair values.

Acquisition-Related Contingent Consideration

Acquisition-related contingent consideration, or “earn-out” liabilities, represent the estimated fair value of future amounts payable for acquisitions of businesses and other interests. Acquisition-related contingent consideration is based on management estimates and entity-specific assumptions, which are Level 3 inputs, and are evaluated on an ongoing basis. As of September 30, 2018 and December 31, 2017, the estimated fair value of the Company’s earn-out liabilities totaled $110.1 million and $117.2 million, respectively, of which $27.5 million and $22.6 million, respectively, was included within other current liabilities. The fair value of the Company’s earn-out liabilities is estimated using income approaches such as discounted cash flows or option pricing models and incorporates significant inputs not observable in the market. Key assumptions include the discount rate and probability-weighted EBITDA projections. Significant changes in any of these assumptions could result in a significantly higher or lower potential earn-out liability. As of September 30, 2018, the range of potential undiscounted earn-out liabilities was estimated to be between $23 million and $173 million; however, there is no maximum payment amount.

Acquisition-related contingent consideration activity consists primarily of additions from new business combinations and acquisitions of other interests; payments; and changes in the expected fair value of future earn-out obligations. Fair value adjustments for earn-out liabilities that relate to circumstances that developed after the date of acquisition are recorded within other income or expense, as appropriate. Fair value adjustments for earn-out liabilities that relate to new information obtained about the facts and circumstances that existed as of the date of acquisition, which are referred to as measurement period adjustments, are recorded to goodwill. There were no additions to acquisition-related contingent consideration from new business combinations for the three month period ended September 30, 2018, and additions for the nine month period ended September 30, 2018 totaled approximately $1.5 million. For the three and nine month periods ended September 30, 2017, additions to acquisition-related contingent consideration from new business combinations totaled approximately $64.6 million and $89.6 million, respectively. For the three month period ended September 30, 2018, measurement period adjustments related to acquisition-related contingent consideration totaled an increase of approximately $2.2 million, and for the nine month period ended September 30, 2018, totaled a net increase of approximately $4.2 million, and related to businesses in the Company’s Oil and Gas and Power Generation and Industrial segments. Fair value adjustments related to acquisition-related contingent consideration, including those related to finalization of completed earn-out arrangements, totaled net increases of approximately $5.9 million and $10.3 million for the three and nine month periods ended September 30, 2018, respectively, primarily for businesses in the Company’s Oil and Gas and Communications segments, and for the three and nine month periods ended September 30, 2017, totaled net decreases of approximately $3.0 million and $11.6 million, respectively, for businesses in the Company’s Communications and Electrical Transmission segments. There were no payments of acquisition-related contingent consideration during the three month periods ended September 30, 2018 or 2017, and payments of acquisition-related contingent consideration during the nine month periods ended September 30, 2018 and 2017 totaled $23.1 million and $18.8 million, respectively.

Equity Investments

The Company’s equity investments as of September 30, 2018 include: (i) the Company’s 33% equity interests in Trans-Pecos Pipeline, LLC (“TPP”) and Comanche Trail Pipeline, LLC (“CTP,” and together with TPP, the “Waha JVs”), which are accounted for as equity method investments; (ii) a $15 million investment in Cross Country Infrastructure Services, Inc. (“CCI”); (iii) the Company’s interests in certain proportionately consolidated non-controlled contractual joint ventures; (iv) the Company’s equity interests in Pensare Acquisition Corp. (“Pensare”); and (v) certain other equity investments. See Note 15 - Related Party Transactions for additional information related to certain of the Company’s equity investments.

The fair values of the Company’s equity investments are not readily determinable. The Company’s equity investments, other than those that are proportionately consolidated, or those accounted for as equity method investments or under the fair value option, are measured at cost, adjusted for changes from observable market transactions, less impairment (“adjusted cost basis”). The Company evaluates its investments for impairment by considering a variety of factors, including the earnings capacity of the related investments. Realized and unrealized fair market value gains or losses related to the Company’s equity investments are recognized in other income or expense. Fair value measurements for the Company’s equity investments are classified within Level 3 of the fair value hierarchy based on the nature of the fair value inputs. For the nine month period ended September 30, 2018, there were no upward or downward adjustments related to, or impairments of, the Company’s equity investments measured on an adjusted cost basis. The aggregate carrying value of the Company’s equity investments as of September 30, 2018 and December 31, 2017 totaled approximately $197 million and $141 million, respectively, including approximately $18 million of equity investments measured on an adjusted cost basis for both periods.

The Waha JVs. The Waha JVs own and operate two pipelines and a header system that transport natural gas to the Mexican border for export, for which operations commenced in the first half of 2017. For both the three month periods ended September 30, 2018 and 2017, the Company made no equity contributions to these joint ventures, and for the nine month periods ended September 30, 2018 and 2017, made equity contributions totaling $24.5 million and $73.3 million, respectively. The Company previously issued letters of credit in connection with its equity commitments in the Waha JVs. As of September 30, 2018, there were no letters of credit remaining, and as of December 31, 2017, $19 million in letters of credit were outstanding.

Equity in earnings related to the Company’s proportionate share of income from the Waha JVs, which is included within the Company’s Other segment, totaled approximately $7.7 million and $7.4 million for the three month periods ended September 30, 2018 and 2017, respectively, and totaled $19.1 million and $15.1 million for the nine month periods ended September 30, 2018 and 2017, respectively. Cumulative undistributed earnings from the Waha JVs totaled $25.1 million as of September 30, 2018. For the three and nine month periods ended September 30, 2018, the Company received $3.2 million and $10.9 million, respectively, in distributions of earnings from the Waha JVs, which amounts are included within operating cash flows. The Company’s net investment in the Waha JVs, which differs from its proportionate share of the net assets of the Waha JVs, due primarily to capitalized investment costs, totaled approximately $168 million and $121 million as of September 30, 2018 and December 31, 2017, respectively. Certain subsidiaries of MasTec have provided pipeline construction services to the Waha JVs. Revenue recognized in connection with work performed for the Waha JVs, including intercompany eliminations, totaled $3.6 million and $255.2 million for the three and nine month periods ended September 30, 2017, respectively, and for the three and nine month periods ended September 30, 2018, was de minimis. As of September 30, 2018 and December 31, 2017, related receivables, net of billings in excess of costs and earnings, totaled $0.1 million and $2.8 million, respectively.

TPP and CTP are party to separate non-recourse financing facilities, each of which are secured by pledges of the equity interests in the respective entities, as well as a first lien security interest over virtually all of TPP’s and CTP’s assets. The Waha JVs are also party to certain interest rate swaps, which are accounted for as qualifying cash flow hedges. The Company reflects its proportionate share of any unrealized fair market value gains or losses from fluctuations in interest rates associated with these swaps within other comprehensive income or loss, as appropriate. For the three and nine month periods ended September 30, 2018, the Company’s proportionate share of unrecognized unrealized activity on these interest rate swaps was a gain of approximately $4.1 million and $18.1 million, respectively, or $3.1 million and $13.8 million, net of tax, respectively. For the three and nine month periods ended September 30, 2017, the Company’s proportionate share of unrecognized unrealized activity on these interest rate swaps was a gain of approximately $1.3 million and a loss of approximately $2.1 million, respectively, or a gain of $0.8 million and a loss of $1.3 million, net of tax, respectively.

Other Investments. During the third quarter of 2017, the Company paid $2.0 million for approximately 4% of the common stock of Pensare and warrants to purchase 2.0 million shares of Pensare common stock, which is a special purpose acquisition company focusing on transactions in the telecommunications industry. José R. Mas, MasTec’s Chief Executive Officer, is a director of Pensare. The shares of common stock purchased by MasTec are not transferable or salable until one year after Pensare successfully completes a business combination transaction, with limited exceptions, as specified in the agreement. The warrants are exercisable at a purchase price of $11.50 per share after Pensare successfully completes a business combination. Both the warrants and shares expire and/or are effectively forfeitable if Pensare does not successfully complete a business combination by February 1, 2019. The shares, which are measured on an adjusted cost basis, and the warrants, which are derivative financial instruments, are included within other long-term assets in the Company’s consolidated financial statements as of September 30, 2018. Due to the nature of the restrictions, the fair value of the shares is not readily determinable, and there were no upward or downward adjustments related to these shares during either of the three or nine month periods ended September 30, 2018. As of September 30, 2018, the warrants approximated their initially recorded fair values, as determined based on observable and unobservable inputs, including market volatility and the rights and obligations of the warrants, which are Level 3 inputs.

During the second quarter of 2018, the Company invested $10.0 million for a 38.5% interest in LifeShield, LLC (“LifeShield”), a home security company, which is measured under the fair value option. Management believes that the fair value option provides an accurate reflection of the economic performance of LifeShield and the value of the Company’s equity interest in the business. To determine the fair value of this investment, the Company estimates the fair value of the entity considering both an income approach, based on discounted cash flows, and a market approach, based on market multiples. The resulting fair value estimates are then evaluated to derive a representative fair value estimate of the entity and the Company’s related investment. As of September 30, 2018, the fair value of this investment was determined to approximate its purchase price.

In connection with the 2014 acquisition of Pacer Construction Holdings Corporation and its affiliated operating companies (collectively, “Pacer”), the Company acquired an investment, for which the Company now has minimal involvement, that is in the final stages of being liquidated and is being managed by a receiver. The Company regularly reviews this investment for potential changes in expected recovery estimates, and during the nine month period ended September 30, 2018, recorded $0.9 million of expense related to changes in expected recovery estimates, and during the nine month period ended September 30, 2017, recorded $5.8 million of expense. The Company received $5.4 million of proceeds from the receiver during the nine month period ended September 30, 2018, and received $12.1 million of proceeds during the nine month period ended September 30, 2017. The net carrying value of this asset, which is included within other current assets, totaled $3.0 million and $9.6 million as of September 30, 2018 and December 31, 2017, respectively.

Senior Notes

As of both September 30, 2018 and December 31, 2017, the gross carrying amount of the Company’s 4.875% senior notes due March 15, 2023 (the “4.875% Senior Notes”), which are measured at fair value on a non-recurring basis, totaled $400 million. As of September 30, 2018 and December 31, 2017, the estimated fair value of the 4.875% Senior Notes, based on Level 1 inputs, totaled $401.0 million and $410.0 million, respectively.