v3.19.1
Document and Entity Information - shares
3 Months Ended
Mar. 31, 2019
May 06, 2019
Document Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q1  
Entity Registrant Name WATSCO INC  
Entity Central Index Key 0000105016  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Trading Symbol WSO  
Entity Emerging Growth Company false  
Entity Small Business false  
Common Stock [Member]    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   32,228,694
Common Class B [Member]    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   5,420,019