Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2019
Feb. 04, 2020
Jun. 28, 2019
Document And Entity Information      
Document Type 10-K    
Document Period End Date Dec. 31, 2019    
Entity Registrant Name PC CONNECTION INC    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 388,435,865
Entity Common Stock, Shares Outstanding   26,344,841  
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2019    
Document Fiscal Period Focus FY    
Entity Central Index Key 0001050377    
Amendment Flag false