Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Aug. 06, 2020
Document Information
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
Document Transition Report	false
Entity File Number	0-30777
Entity Registrant Name	PACIFIC MERCANTILE BANCORP
Entity Incorporation, State	CA
Entity Tax Identification Number	33-0898238
Entity Address, Street Address	949 South Coast Drive
Entity Address, Suite	Suite 300
Entity Address, City	Costa Mesa
Entity Address, State	CA
Entity Address, Postal Zip Code	92626
City Area Code	714
Local Phone Number	438-2500
Title of each class	Common Stock, without par value
Trading Symbol(s)	PMBC
Name of each exchange on which registered	NASDAQ
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 Central Index Key	0001109546
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false
Common Stock
Document Information
Entity Common Stock, Shares Outstanding (in shares)		22,157,649
Nonvoting Common Stock
Document Information
Entity Common Stock, Shares Outstanding (in shares)		1,467,155