Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Trading Symbol	GRUB
Entity Registrant Name	GRUBHUB INC.
Entity Central Index Key	0001594109
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		93,347,973
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	1-36389
Entity Tax Identification Number	46-2908664
Entity Address, Address Line One	111 W. Washington Street
Entity Address, Address Line Two	Suite 2100
Entity Address, City or Town	Chicago
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60602
City Area Code	877
Local Phone Number	585-7878
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Security Exchange Name	NYSE
Entity Incorporation, State or Country Code	DE
Document Transition Report	false
Document Quarterly Report	true
Entity Interactive Data Current	Yes