Document and Entity Information	9 Months Ended
	Sep. 30, 2019 shares
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Registrant Name	IMPINJ INC
Entity Central Index Key	0001114995
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Incorporation, State or Country Code	DE
Entity Common Stock, Shares Outstanding	22,128,284
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Document Transition Report	false
Document Quarterly Report	true
Trading Symbol	PI
Entity Address, State or Province	WA
Entity File Number	001-37824
Entity Tax Identification Number	91-2041398
Entity Address, Address Line One	400 Fairview Avenue North
Entity Address, Address Line Two	Suite 1200
Entity Address, City or Town	Seattle
Entity Address, Postal Zip Code	98109
City Area Code	206
Local Phone Number	517-5300
Title of 12(b) Security	Common Stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Entity Interactive Data Current	Yes