Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Oct. 31, 2019
Document Documentand Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Registrant Name	GREENHILL & CO INC
Entity Central Index Key	0001282977
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		19,080,845
Emerging Growth Company	false
Smaller Reporting Company	false
Entity Shell Company	false