v3.19.3
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Nov. 01, 2019
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  
Trading Symbol TOCA  
Entity Registrant Name Tocagen Inc  
Entity Central Index Key 0001419041  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding   23,897,771
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period true  
Entity Shell Company false  
Entity Current Reporting Status Yes  
Entity File Number 001-38052  
Entity Tax Identification Number 26-1243872  
Entity Address, Address Line One 4242 Campus Point Court  
Entity Address, Address Line Two Suite 500  
Entity Address, City or Town San Diego  
Entity Address, State or Province CA  
Entity Address, Postal Zip Code 92121  
City Area Code 858  
Local Phone Number 412-8400  
Document Quarterly Report true  
Document Transition Report false  
Entity Incorporation, State or Country Code DE  
Title of 12(b) Security Common Stock, par value $0.001 per share  
Security Exchange Name NASDAQ  
Entity Interactive Data Current Yes