Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Effective income tax rate	0.80%	36.10%
Benefit related to net operating losses that carried back as result of CARES Act		$ 6,800,000
Tax deficiencies on stock-based compensation	$ 0	$ (2,500,000)
Income tax examination description	The Company is currently under examination by the Internal Revenue Service for its federal income tax return for the tax year ended December 31, 2017. The Company does not believe, but cannot predict with certainty, that there will not be any additional tax liabilities, penalties and/or interest as a result of the audit.

Coronavirus aid, relief, and economic security act, impact on net operating loss carryback benefit.

No definition available.

Name:	grub_CoronavirusAidReliefAndEconomicSecurityActImpactOnNetOperatingLossCarrybackBenefit
Namespace Prefix:	grub_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

+ Details

Name:	us-gaap_EffectiveIncomeTaxRateContinuingOperations
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of tax benefit from exercise of option under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=SL79508275-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromExerciseOfStockOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_IncomeTaxDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

A brief description of status of the tax examination, significant findings to date, and the entity's position with respect to the findings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

+ Details

Name:	us-gaap_IncomeTaxExaminationDescription
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration