Retirement Plan - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Maximum percentage of eligible compensation participants may contribute	50.00%
Greenhill & Co., LLC [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Incurred costs for contributions to retirement plan	$ 300,000	$ 300,000	$ 200,000
Contributions due to Retirement Plan included in compensation payable	100,000	200,000
Greenhill And Company International LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions due to Retirement Plan included in compensation payable	0	0
Costs incurred for pension	700,000	600,000	700,000
Greenhill & Co. Australia Pty Limited [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions due to Retirement Plan included in compensation payable	0	0
Costs incurred for pension	600,000	600,000	400,000
Greenhill & Co. Australia Pty Limited [Member] | Pension Plans, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of compulsory contribution for superannuation on employees gross earnings	9.00%
Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Company's maximum matching contributions per employee	$ 1,000