Document and Entity Information - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Mar. 12, 2018
Jun. 30, 2017
Document And Entity Information      
Entity Registrant Name PCM, INC.    
Entity Central Index Key 0000937941    
Document Type 10-K    
Document Period End Date Dec. 31, 2017    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Entity Filer Category Accelerated Filer    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filer No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 186,600
Entity Common Stock, Shares Outstanding   11,792,105  
Trading Symbol PCMI    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2017