Document and Entity Information
Jun. 12, 2019
Cover [Abstract]  
Amendment Flag false
Entity Central Index Key 0001560241
Document Type 8-K/A
Document Period End Date Jun. 12, 2019
Entity Registrant Name G1 THERAPEUTICS, INC.
Entity Incorporation, State or Country Code DE
Entity File Number 001-38096
Entity Tax Identification Number 26-3648180
Entity Address, Address Line One 700 Park Offices Drive
Entity Address, Address Line Two Suite 200
Entity Address, City or Town Research Triangle Park
Entity Address, State or Province NC
Entity Address, Postal Zip Code 27709
City Area Code 919
Local Phone Number 213-9835
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Title of 12(b) Security Common stock, $0.0001 par value
Trading Symbol GTHX
Security Exchange Name NASDAQ
Entity Emerging Growth Company false