Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 30, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-32147
Entity Registrant Name	GREENHILL & CO., INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	51-0500737
Entity Address, Address Line One	1271 Avenue of Americas
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10020
City Area Code	(212)
Local Phone Number	389-1500
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	GHL
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		18,972,158
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001282977
Current Fiscal Year End Date	--12-31