Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 14, 2020	Jun. 30, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
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 Shell Company	false
Entity Common Stock, Shares Outstanding		91,840,273
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Interactive Data Current	Yes
Entity Public Float			$ 5,349,074,861
Entity File Number	1-36389
Entity Tax Identification Number	46-2908664
Entity Incorporation, State or Country Code	DE
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
Documents Incorporated by Reference	Portions of the Registrant’s Definitive Proxy Statement relating to the Annual Meeting of Stockholders, scheduled to be held on May 19, 2020, are incorporated by reference into Part III of this Annual Report on Form 10-K.