BASIS OF PRESENTATION (Policies)	6 Months Ended
BASIS OF PRESENTATION (Policies)	Jun. 30, 2018
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 June 30, 2018 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 2017 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 six months ended June 30, 2018 are not necessarily indicative of the results to be expected for the year ending December 31, 2018. 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.
Equity Method Investments	Equity Method Investments Investments in which we have the ability to exercise significant influence, but do not control, are accounted for under the equity method of accounting and are included in other assets in our consolidated balance sheets. Under this method of accounting, our proportionate share of the net income or loss of the investee is included in other income in our consolidated statements of income. The excess, if any, of the carrying amount of our investment over our ownership percentage in the underlying net assets of the investee is attributed to certain fair value adjustments with the remaining portion recognized as goodwill.
Reclassifications	Reclassifications Certain reclassifications of prior year amounts have been made to conform to the 2018 presentation. These reclassifications had no effect on net income or earnings per share as previously reported.
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 self-insurance programs and the valuation of goodwill and indefinite 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 Revenue Recognition In May 2014, the Financial Accounting Standards Board (the “FASB”) issued a standard on revenue recognition that provides a single, comprehensive revenue recognition model for all contracts with customers. The standard is principle-based and provides a five-step model to determine the measurement of revenue and timing of when it is recognized. In 2015 and 2016, the FASB issued several updates to this standard. The adoption of this standard and its related amendments (collectively, the “New Revenue Standard”) on January 1, 2018 did not result in the recognition of a cumulative adjustment to opening retained earnings under the modified retrospective approach, nor did it have a significant impact on our consolidated net income, balance sheet or cash flow. See Note 2. Financial Instruments In January 2016, the FASB issued guidance related to certain aspects of recognition, measurement, presentation and disclosure of financial instruments. Most prominent among the changes to the standard is the requirement that changes in the fair value of equity investments, with certain exceptions, be recognized through net income rather than other comprehensive income. This guidance must be applied using a modified retrospective approach through a cumulative-effect adjustment to retained earnings and became effective for interim and annual periods beginning after December 15, 2017. The adoption of this guidance did not have a material impact on our consolidated financial statements. A cumulative-effect adjustment captured the previously held unrealized losses of $301 related to our equity investment carried at fair value. See Note 4. Stock Compensation In May 2017, the FASB issued guidance to clarify when to account for a change to the terms or conditions of a share-based payment award as a modification. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. This guidance must be applied prospectively and became effective for interim and annual periods beginning after December 15, 2017. The adoption of this guidance did not have a material impact on our consolidated financial statements. Derivatives and Hedging In August 2017, the FASB issued guidance to simplify the accounting for hedging derivatives. This guidance is effective prospectively and is effective for interim and annual periods beginning after December 15, 2018 with early adoption permitted. We elected to adopt this guidance during the quarter ended June 30, 2018, which did not have a material impact on our consolidated financial statements. Recently Issued Accounting Standards Not Yet Adopted Leases In February 2016, the 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. We will apply this guidance using a modified retrospective approach, and it will be effective for interim and annual periods beginning after December 15, 2018. Based on our preliminary assessment of our lease portfolio, we expect the adoption of this guidance to have a material impact on our consolidated balance sheets due to the recognition of right-of-use assets and lease liabilities. However, we do not expect a material impact on our consolidated statements of income. We are in the process of collecting data and designing processes and controls to account for our leases in accordance with the new guidance. Our current minimum lease commitments are disclosed in Note 16 to our Annual Report on Form 10-K for the year ended December 31, 2017. 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.
Self-Insurance	Self-Insurance Self-insurance reserves are maintained relative to company-wide casualty insurance and health benefit programs. The level of exposure from catastrophic events is limited by the purchase of stop-loss and aggregate liability reinsurance coverage. When estimating the self-insurance liabilities and related reserves, management considers a number of factors, which include historical claims experience, demographic factors, severity factors and valuations provided by independent third-party actuaries. Management reviews its assumptions with its independent third-party actuaries to evaluate whether the self-insurance reserves are adequate. If actual claims or adverse development of loss reserves occur and exceed these estimates, additional reserves may be required.