Fair Value of Financial Instruments	9 Months Ended
Fair Value of Financial Instruments	Sep. 30, 2019
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 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. Acquisition-Related Contingent Consideration Acquisition-related contingent consideration, or “earn-outs,” represent the estimated fair value of future amounts payable for acquisitions of businesses and other interests. Acquisition-related contingent consideration amounts are based on Level 3 inputs, including management’s estimates and entity-specific assumptions, and are evaluated on an ongoing basis. As of September 30, 2019 and December 31, 2018, the estimated fair value of the Company’s earn-out liabilities totaled $151.9 million and $118.1 million, respectively, of which $57.5 million and $29.6 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, which incorporate significant inputs not observable in the market. Key assumptions include the discount rate and probability-weighted projections of earnings before interest, taxes, depreciation and amortization (“EBITDA”). Significant changes in any of these assumptions could result in significantly higher or lower potential earn-out liabilities. As of September 30, 2019, the range of potential undiscounted earn-out liabilities was estimated to be between $48 million and $225 million; however, there is no maximum payment amount. Acquisition-related contingent consideration activity consists primarily of additions from new business combinations; changes in the expected fair value of future earn-out obligations; and payments. Measurement period adjustments for earn-out liabilities, which are fair value adjustments relating to new information obtained about the facts and circumstances existing as of the date of acquisition for a period of up to one year, are recorded to goodwill. Other revisions to the expected fair values of future earn-out liabilities are reflected as income or expense, as appropriate. Payments of acquisition-related contingent consideration, to the extent they relate to estimated liabilities as of the date of acquisition, are reflected within financing activities in the consolidated statements of cash flows. Payments in excess of acquisition date liabilities are classified within operating activities. There were no additions from new business combinations for the three month periods ended September 30, 2019 or 2018, and for the nine month periods ended September 30, 2019 and 2018, additions totaled $16.2 million and $1.5 million, respectively. Fair value adjustments related to acquisition-related contingent consideration totaled net increases of approximately $11.2 million and $47.6 million, respectively, for the three and nine month periods ended September 30, 2019, and related primarily to businesses in the Company’s Oil and Gas and Communications segments. Fair value adjustments, 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, and related primarily to businesses in the Company’s Oil and Gas and Communications segments. For the three and nine month periods ended September 30, 2018, measurement period adjustments totaled increases of approximately $2.2 million and $4.2 million, net, respectively, and related primarily to businesses in the Company’s Oil and Gas and Power Generation and Industrial segments. There were no payments of acquisition-related contingent consideration in either of the three month periods ended September 30, 2019 or 2018. Payments of acquisition-related contingent consideration totaled $30.0 million and $23.1 million for the nine month periods ended September 30, 2019 and 2018, respectively. Equity Investments The Company’s equity investments as of September 30, 2019 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. Investment Arrangements. From time to time, the Company may participate in selected investment or strategic arrangements, including equity interests in various business entities and participation in contractual joint ventures, some of which may involve the extension of loans or other types of financing arrangements. As of September 30, 2019, the Company determined that certain of its investment arrangements were variable interest entities (“VIEs”). The Company does not, however, have the power to direct the primary activities that most significantly impact the economic performance of these VIEs and the Company is not the primary beneficiary; accordingly, it has not consolidated these VIEs. Equity investments, other than those accounted for as equity method investments or those that are proportionately consolidated, are measured at fair value if their fair values are readily determinable. Equity investments that do not have readily determinable fair values are measured at cost, adjusted for changes from observable market transactions, less impairment (“adjusted cost basis”). As of September 30, 2019 and December 31, 2018, the aggregate carrying value of the Company’s equity investments totaled approximately $184 million and $197 million, respectively, including approximately $18 million of equity investments measured on an adjusted cost basis as of both September 30, 2019 and December 31, 2018. There were no impairments of, or material changes in the fair value of these investments during either of the nine month periods ended September 30, 2019 or 2018. 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 both the three month periods ended September 30, 2019 and 2018, the Company made no equity contributions to the Waha JVs, and for the nine month periods ended September 30, 2019 and 2018, the Company made equity contributions totaling $1.3 million and $24.5 million, respectively. 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 $6.9 million and $7.7 million for the three month periods ended September 30, 2019 and 2018, respectively, and totaled $19.8 million and $19.1 million for the nine month periods ended September 30, 2019 and 2018, respectively. Cumulative undistributed earnings from the Waha JVs, which represents cumulative equity in earnings for the Waha JVs less distributions of earnings, totaled $42.2 million as of September 30, 2019. Distributions of earnings from the Waha JVs, which are included within operating cash flows, totaled $1.5 million and $3.2 million for the three month periods ended September 30, 2019 and 2018, respectively, and totaled $7.5 million and $10.9 million for the nine month periods ended September 30, 2019 and 2018, respectively. 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 $162 million and $168 million as of September 30, 2019 and December 31, 2018, respectively. The Waha JVs 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 their 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, 2019, the Company’s proportionate share of unrecognized unrealized activity on these interest rate swaps totaled losses of approximately $9.4 million and $28.2 million, respectively, or $7.1 million and $21.3 million, net of tax, respectively. 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 totaled gains of approximately $4.1 million and $18.1 million, respectively, or $3.1 million and $13.8 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 transaction. Both the warrants and the shares contain an expiration and/or forfeiture clause without the successful completion of a business combination transaction, for which the completion date was extended from August 1, 2019 to December 1, 2019 in the third quarter of 2019. On July 25, 2019, Pensare entered into a business combination agreement with Stratos Management Systems, Inc. and its operating companies, which do business as Computex Technology Solutions (collectively, “Computex”), an information technology service provider, the completion of which is pending shareholder approval. Pensare also announced that it has entered into a non-binding letter of intent to acquire a separate company that provides information technology services. During the nine month period ended September 30, 2019, certain holders of Pensare’s redeemable common stock elected to redeem their shares, the effect of which was to increase the Company’s ownership interest in Pensare to approximately 21%. The Company does not have the ability to exert significant influence over the operating and financial policies of Pensare, therefore, the shares are measured on an adjusted cost basis. The warrants, which are derivative financial instruments, and the shares, are both included within other long-term assets in the Company’s consolidated financial statements as of September 30, 2019. Due to the nature of the restrictions, the fair value of the shares is not readily determinable. The fair value of the warrants is determined based on observable and unobservable Level 3 inputs, including market volatility and the rights and obligations of the warrants. For both the three and nine month periods ended September 30, 2019 and 2018, there were no material changes in the fair value of the Company’s investment in Pensare. During the second quarter of 2018, the Company invested $10.0 million for an equity interest of approximately 40% in LifeShield, LLC (“LifeShield”), a home security company, which was measured under the fair value option. As of December 31, 2018, the fair value of this investment was determined to approximate its purchase price. In February 2019, the Company sold its equity interest in LifeShield for approximately $11 million, subject to customary escrow arrangements. Senior Notes As of both September 30, 2019 and December 31, 2018, 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, 2019 and December 31, 2018, the estimated fair value of the 4.875% Senior Notes, based on Level 1 inputs, totaled $407.5 million and $392.0 million, respectively.

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.