Fair Value of Financial Instruments	3 Months Ended
Mar. 31, 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, cash collateral deposited with insurance carriers, life insurance assets, equity investments, 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 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, deferred compensation plan assets and liabilities and outstanding balances on its credit facilities approximate their fair values. Assets and Liabilities Measured at Fair Value on a Recurring Basis As of March 31, 2018 and December 31, 2017, financial instruments required to be measured at fair value on a recurring basis consisted primarily of acquisition-related contingent consideration, or “earn-out” liabilities, which represents the estimated fair value of future amounts payable for acquisitions of businesses and other interests. Acquisition-related contingent consideration liabilities are based on management estimates and entity-specific assumptions, which are Level 3 inputs, and are evaluated on an ongoing basis. As of March 31, 2018 and December 31, 2017, the estimated fair value of the Company’s earn-out liabilities totaled $121.4 million and $117.2 million, respectively, of which $23.8 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 March 31, 2018, the range of potential undiscounted earn-out liabilities was estimated to be between $28 million and $214 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. For the three month period ended March 31, 2018, additions to acquisition-related contingent consideration from new business combinations totaled approximately $1.5 million and additions from measurement period adjustments totaled approximately $2.7 million. Other acquisition-related contingent consideration activity was de minimis in both the three month periods ended March 31, 2018 and 2017. Assets and Liabilities Measured at Fair Value on a Non-Recurring Basis Assets and liabilities recognized or disclosed at fair value on a non-recurring basis, for which remeasurement occurs in the event of an impairment or other measurement event, if applicable, include items such as equity investments, life insurance assets, long-lived assets, goodwill, other intangible assets and debt. As of both March 31, 2018 and December 31, 2017, the gross carrying amount of the Company’s 4.875% Senior Notes totaled $400 million. As of March 31, 2018 and December 31, 2017, the estimated fair value of the 4.875% Senior Notes, based on Level 1 inputs, totaled $400.0 million and $410.0 million, respectively. Equity Investments The Company’s equity investments as of March 31, 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 its 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 below and Note 15 - Related Party Transactions. The fair values of the Company’s equity investments are not readily determinable. The Company’s equity investments, other than those accounted for as equity method investments or those that are proportionately consolidated, are measured at cost, adjusted for changes from observable market transactions, less impairment (“adjusted cost basis”), with realized and unrealized gains or losses recognized in other income or expense. Fair value measurements for the Company’s equity investments are classified within Level 3 in the fair value hierarchy based on the nature of the fair value inputs. For the three month period ended March 31, 2018, the Company was not aware of any observable market transactions related to, or impairments of, its equity investments. The aggregate carrying value of the Company’s equity investments as of March 31, 2018 and December 31, 2017 totaled approximately $163 million and $141 million, respectively, including approximately $18 million of equity investments measured on an adjusted cost basis as of 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. These pipelines, which interconnect with pipelines in Mexico, commenced operations in 2017. For the three month periods ended March 31, 2018 and 2017, the Company made equity contributions to these joint ventures of approximately $14.8 million and $53.3 million, respectively. In connection with its equity commitments in the Waha JVs, the Company has, in the past, issued letters of credit, of which $19 million were outstanding as of December 31, 2017. As of March 31, 2018, there were no letters of credit remaining, and all of the Company’s equity commitments had been satisfied. 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 $5.6 million and $1.6 million for the three month periods ended March 31, 2018 and 2017, respectively. Cumulative undistributed earnings from the Waha JVs totaled $16.8 million as of March 31, 2018. For the three month period ended March 31, 2018, the Company received $5.7 million in distributions of earnings from the Waha JVs. The Company’s net investment in the Waha JVs, which differs from its proportionate share of the net assets of the Waha JVs due largely to capitalized investment costs, totaled approximately $144 million and $121 million as of March 31, 2018 and December 31, 2017, respectively. Certain subsidiaries of MasTec have provided pipeline construction services to the Waha JVs. For the three month period ended March 31, 2018, revenue recognized in connection with work performed for the Waha JVs, including intercompany eliminations, was de minimis, and for the three month period ended March 31, 2017, totaled $151.4 million. As of March 31, 2018 and December 31, 2017, related receivables, net of billings in excess of costs and earnings, totaled $0.2 million and $2.8 million, respectively. TPP and CTP are party to separate non-recourse financing facilities, which are each 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. The Company’s proportionate share of unrecognized unrealized activity on these interest rate swaps for the three month periods ended March 31, 2018 and 2017 were gains of approximately $10.1 million and $1.0 million, respectively, or $7.7 million and $0.6 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. 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 purchased by MasTec 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 warrants, which are derivative financial instruments, and the shares, which are measured on an adjusted cost basis, are included within other long-term assets in the Company’s consolidated financial statements as of March 31, 2018. The fair value of the warrants, as determined based on Level 3 inputs, approximated their initial cost basis as of March 31, 2018. The fair value of the shares is not readily determinable due to the nature of the restrictions. José R. Mas, MasTec’s Chief Executive Officer, is a director of Pensare. In connection with the 2014 acquisition of Pacer Construction Holdings Corporation and its affiliated operating companies (collectively, “Pacer”), the Company acquired an investment that is in the final stages of being liquidated and is being managed by a receiver. The Company received $5.4 million and $12.1 million of proceeds from the receiver in the three month periods ended March 31, 2018 and 2017, respectively. The net carrying value, which is included within other current assets, totaled $4.0 million and $9.6 million as of March 31, 2018 and December 31, 2017, respectively.

Note 4 – Fair Value of Financial Instruments

The Company’s financial instruments include cash and cash equivalents, accounts and notes receivable, cash collateral deposited with insurance carriers, life insurance assets, equity investments, 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 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, deferred compensation plan assets and liabilities and outstanding balances on its credit facilities approximate their fair values.

Assets and Liabilities Measured at Fair Value on a Recurring Basis

As of March 31, 2018 and December 31, 2017, financial instruments required to be measured at fair value on a recurring basis consisted primarily of acquisition-related contingent consideration, or “earn-out” liabilities, which represents the estimated fair value of future amounts payable for acquisitions of businesses and other interests. Acquisition-related contingent consideration liabilities are based on management estimates and entity-specific assumptions, which are Level 3 inputs, and are evaluated on an ongoing basis. As of March 31, 2018 and December 31, 2017, the estimated fair value of the Company’s earn-out liabilities totaled $121.4 million and $117.2 million, respectively, of which $23.8 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 March 31, 2018, the range of potential undiscounted earn-out liabilities was estimated to be between $28 million and $214 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. For the three month period ended March 31, 2018, additions to acquisition-related contingent consideration from new business combinations totaled approximately $1.5 million and additions from measurement period adjustments totaled approximately $2.7 million. Other acquisition-related contingent consideration activity was de minimis in both the three month periods ended March 31, 2018 and 2017.

Assets and Liabilities Measured at Fair Value on a Non-Recurring Basis

Assets and liabilities recognized or disclosed at fair value on a non-recurring basis, for which remeasurement occurs in the event of an impairment or other measurement event, if applicable, include items such as equity investments, life insurance assets, long-lived assets, goodwill, other intangible assets and debt.

As of both March 31, 2018 and December 31, 2017, the gross carrying amount of the Company’s 4.875% Senior Notes totaled $400 million. As of March 31, 2018 and December 31, 2017, the estimated fair value of the 4.875% Senior Notes, based on Level 1 inputs, totaled $400.0 million and $410.0 million, respectively.

Equity Investments

The Company’s equity investments as of March 31, 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 its 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 below and Note 15 - Related Party Transactions.

The fair values of the Company’s equity investments are not readily determinable. The Company’s equity investments, other than those accounted for as equity method investments or those that are proportionately consolidated, are measured at cost, adjusted for changes from observable market transactions, less impairment (“adjusted cost basis”), with realized and unrealized gains or losses recognized in other income or expense. Fair value measurements for the Company’s equity investments are classified within Level 3 in the fair value hierarchy based on the nature of the fair value inputs. For the three month period ended March 31, 2018, the Company was not aware of any observable market transactions related to, or impairments of, its equity investments. The aggregate carrying value of the Company’s equity investments as of March 31, 2018 and December 31, 2017 totaled approximately $163 million and $141 million, respectively, including approximately $18 million of equity investments measured on an adjusted cost basis as of 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. These pipelines, which interconnect with pipelines in Mexico, commenced operations in 2017. For the three month periods ended March 31, 2018 and 2017, the Company made equity contributions to these joint ventures of approximately $14.8 million and $53.3 million, respectively. In connection with its equity commitments in the Waha JVs, the Company has, in the past, issued letters of credit, of which $19 million were outstanding as of December 31, 2017. As of March 31, 2018, there were no letters of credit remaining, and all of the Company’s equity commitments had been satisfied.

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 $5.6 million and $1.6 million for the three month periods ended March 31, 2018 and 2017, respectively. Cumulative undistributed earnings from the Waha JVs totaled $16.8 million as of March 31, 2018. For the three month period ended March 31, 2018, the Company received $5.7 million in distributions of earnings from the Waha JVs. The Company’s net investment in the Waha JVs, which differs from its proportionate share of the net assets of the Waha JVs due largely to capitalized investment costs, totaled approximately $144 million and $121 million as of March 31, 2018 and December 31, 2017, respectively. Certain subsidiaries of MasTec have provided pipeline construction services to the Waha JVs. For the three month period ended March 31, 2018, revenue recognized in connection with work performed for the Waha JVs, including intercompany eliminations, was de minimis, and for the three month period ended March 31, 2017, totaled $151.4 million. As of March 31, 2018 and December 31, 2017, related receivables, net of billings in excess of costs and earnings, totaled $0.2 million and $2.8 million, respectively.

TPP and CTP are party to separate non-recourse financing facilities, which are each 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. The Company’s proportionate share of unrecognized unrealized activity on these interest rate swaps for the three month periods ended March 31, 2018 and 2017 were gains of approximately $10.1 million and $1.0 million, respectively, or $7.7 million and $0.6 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. 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 purchased by MasTec 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 warrants, which are derivative financial instruments, and the shares, which are measured on an adjusted cost basis, are included within other long-term assets in the Company’s consolidated financial statements as of March 31, 2018. The fair value of the warrants, as determined based on Level 3 inputs, approximated their initial cost basis as of March 31, 2018. The fair value of the shares is not readily determinable due to the nature of the restrictions. José R. Mas, MasTec’s Chief Executive Officer, is a director of Pensare.

In connection with the 2014 acquisition of Pacer Construction Holdings Corporation and its affiliated operating companies (collectively, “Pacer”), the Company acquired an investment that is in the final stages of being liquidated and is being managed by a receiver. The Company received $5.4 million and $12.1 million of proceeds from the receiver in the three month periods ended March 31, 2018 and 2017, respectively. The net carrying value, which is included within other current assets, totaled $4.0 million and $9.6 million as of March 31, 2018 and December 31, 2017, respectively.