Document and Entity Information - shares
3 Months Ended
Mar. 31, 2018
Apr. 25, 2018
Document and Entity Information [Abstract]    
Entity Registrant Name Safety, Income & Growth, Inc.  
Entity Central Index Key 0001688852  
Document Type 10-Q  
Document Period End Date Mar. 31, 2018  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Entity Common Stock, Shares Outstanding   18,190,000
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q1