Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Nov. 05, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	Ra Medical Systems, Inc.
Entity Central Index Key	0001716621
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Trading Symbol	RMED
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		12,689,251
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Entity Emerging Growth Company	true
Entity Small Business	true
Entity Ex transition period	false