Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Aug. 10, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Trading Symbol	SMSI
Entity Registrant Name	SMITH MICRO SOFTWARE, INC.
Entity Central Index Key	0000948708
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		53,546,068
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	00-135525
Entity Tax Identification Number	33-0029027
Entity Address, Address Line One	5800 CORPORATE DRIVE
Entity Address, City or Town	PITTSBURGH
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	15237
City Area Code	412
Local Phone Number	837-5300
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Document Quarterly Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE