Document and Entity Information	3 Months Ended
	Mar. 31, 2019 shares
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	PI
Entity Registrant Name	IMPINJ INC
Entity Central Index Key	0001114995
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding	21,627,172
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false