Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Jul. 27, 2020
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
Document Transition Report	false
Entity File Number	1-34907
Entity Registrant Name	STAG Industrial, Inc.
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	27-3099608
Entity Address, Address Line One	One Federal Street
Entity Address, Address Line Two	23rd Floor
Entity Address, City or Town	Boston,
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02110
City Area Code	617
Local Phone Number	574-4777
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		149,141,565
Entity Central Index Key	0001479094
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Central Index Key	0001479094
Current Fiscal Year End Date	--12-31
Common Stock
Entity Information [Line Items]
Title of 12(b) Security	Common stock, $0.01 par value per share
Trading Symbol	STAG
Security Exchange Name	NYSE
Series C Preferred Stock
Entity Information [Line Items]
Title of 12(b) Security	6.875% Series C Cumulative Redeemable Preferred Stock ($0.01 par value)
Trading Symbol	STAG-PC
Security Exchange Name	NYSE