Retirement Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Greenhill & Co., LLC
Defined Contribution Plan Disclosure [Line Items]
Incurred costs for contributions to retirement plan	$ 600,000	$ 600,000	$ 300,000
Contributions due to Retirement Plan included in compensation payable	200,000	500,000
Greenhill And Company International LLC
Defined Contribution Plan Disclosure [Line Items]
Contributions due to Retirement Plan included in compensation payable	0	0
Costs incurred for pension	300,000	400,000	500,000
Greenhill & Co. Australia Pty Limited
Defined Contribution Plan Disclosure [Line Items]
Contributions due to Retirement Plan included in compensation payable	0	0
Costs incurred for pension	$ 400,000	$ 400,000	$ 500,000
Greenhill & Co. Australia Pty Limited | Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Contribution percent on employees' gross earnings (percent)	9.00%