Document and Entity Information - shares
9 Months Ended
Sep. 30, 2017
Nov. 06, 2017
Document And Entity Information    
Entity Registrant Name PCM, INC.  
Entity Central Index Key 0000937941  
Document Type 10-Q  
Document Period End Date Sep. 30, 2017  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding   11,780,474
Trading Symbol PCMI  
Document Fiscal Period Focus Q3  
Document Fiscal Year Focus 2017