BASIS OF PRESENTATION (Policies)	9 Months Ended
BASIS OF PRESENTATION (Policies)	Sep. 30, 2019
Basis of Consolidation	Basis of Consolidation Watsco, Inc. (collectively with its subsidiaries, “Watsco,” “we,” “us,” or “our”) was incorporated in Florida in 1956 and is the largest distributor of air conditioning, heating and refrigeration equipment and related parts and supplies (“HVAC/R”) in the HVAC/R distribution industry in North America. The accompanying September 30, 2019 interim condensed consolidated unaudited financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Certain information and note disclosures normally included in the annual financial statements prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) have been condensed or omitted pursuant to those rules and regulations, but we believe the disclosures made are adequate to make the information presented not misleading. In the opinion of management, all adjustments, consisting of normal and recurring adjustments, necessary for a fair presentation have been included in the condensed consolidated unaudited financial statements included herein. These statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in our 2018 Annual Report on Form 10-K. The condensed consolidated unaudited financial statements contained in this report include the accounts of Watsco, all of its wholly owned subsidiaries and the accounts of three joint ventures with Carrier Corporation (“Carrier”), in each of which Watsco maintains a controlling interest. All significant intercompany balances and transactions have been eliminated in consolidation. The results of operations for the quarter and nine months ended September 30, 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019. Sales of residential central air conditioners, heating equipment, and parts and supplies are seasonal. Furthermore, results of operations can be impacted favorably or unfavorably based on weather patterns, primarily during the Summer and Winter selling seasons. Demand related to the residential central air conditioning replacement market is typically highest in the second and third quarters, and demand for heating equipment is usually highest in the fourth quarter. Demand related to the new construction market is generally evenly distributed throughout the year, subject to weather and economic conditions, including their effect on the number of housing completions.
Use of Estimates	Use of Estimates The preparation of condensed consolidated unaudited financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated unaudited financial statements and the reported amounts of revenues and expenses for the reporting period. Significant estimates include valuation reserves for accounts receivable, inventories and income taxes, reserves related to loss contingencies and the valuation of goodwill, indefinite - lived intangible assets and long-lived intangible assets. While we believe that these estimates are reasonable, actual results could differ from such estimates.
Recently Adopted Accounting Standards and Recently Issued Accounting Standards Not Yet Adopted	Recently Adopted Accounting Standards Leases In February 2016, the Financial Accounting Standards Board (“FASB”) issued guidance on accounting for leases, which requires lessees to recognize most leases on their balance sheets for the rights and obligations created by those leases. In July 2018, the FASB issued updated guidance that provides an additional transition method of adoption that allows entities to initially apply the standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings. The adoption of this standard and its related amendments (collectively, the “New Lease Standard”) on January 1, 2019 did not result in the recognition of a cumulative adjustment to opening retained earnings under the additional transition method, nor did it have a significant impact on our consolidated statements of income or cash flows. See Note 2. Recently Issued Accounting Standards Not Yet Adopted Intangibles—Goodwill and Other In January 2017, the FASB issued guidance to simplify the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. Under this updated standard, an entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value, but the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. An entity also should consider income tax effects from any tax-deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if any. This guidance is effective prospectively and is effective for interim and annual periods beginning after December 15, 2019 with early adoption permitted. We do not expect the adoption of this guidance to have a material impact on our consolidated financial statements.