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Summary of Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2017
USD ($)
Entity
State
Store
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Significant Accounting Policies [Line Items]      
Number of joint ventures | Entity 3    
Allowance for doubtful accounts $ 6,049,000 $ 6,169,000  
Capitalized vendor rebates 11,621,000 9,926,000  
Goodwill and intangible assets impairment 0 0 $ 0
Advertising expense 24,677,000 22,242,000 21,150,000
Shipping and handling costs $ 47,670,000 $ 42,809,000 $ 41,345,000
Minimum | Buildings and Improvements      
Significant Accounting Policies [Line Items]      
Estimated useful lives in years 3 years    
Minimum | Other Depreciable Assets      
Significant Accounting Policies [Line Items]      
Estimated useful lives in years 3 years    
Minimum | Furniture and Fixtures      
Significant Accounting Policies [Line Items]      
Estimated useful lives in years 5 years    
Maximum | Buildings and Improvements      
Significant Accounting Policies [Line Items]      
Estimated useful lives in years 40 years    
Maximum | Other Depreciable Assets      
Significant Accounting Policies [Line Items]      
Estimated useful lives in years 10 years    
Maximum | Furniture and Fixtures      
Significant Accounting Policies [Line Items]      
Estimated useful lives in years 7 years    
Watsco, Inc.      
Significant Accounting Policies [Line Items]      
Number of locations from which entity operates | Store 560    
Number of states in which entity operates | State 37