Document and Entity Information - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Mar. 13, 2019	Jun. 30, 2018
Document And Entity Information
Entity Registrant Name	PCM, INC.
Entity Central Index Key	0000937941
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity a Well-known Seasoned Issuer	No
Entity a Voluntary Filer	No
Entity's Reporting Status Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business Flag	true
Entity Emerging Growth Company	false
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Public Float			$ 119,600
Entity Common Stock, Shares Outstanding		12,245,979
Trading Symbol	PCMI
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2018