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Retirement Plan Retirement Plan - Contribution Plan (Details) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Defined Contribution Plan Disclosure [Line Items]      
Maximum percentage of eligible compensation participants may contribute (up to 50%) (percent) 75.00%ghl_MaximumEmployeeEarningsContributionFor401K    
Maximum      
Defined Contribution Plan Disclosure [Line Items]      
Company's maximum matching contributions per employee (up to $1,000) $ 1,000ghl_Companys401KEmployerMatchExpense
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Greenhill & Co., LLC      
Defined Contribution Plan Disclosure [Line Items]      
Incurred costs for contributions to retirement plan 200,000us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis
= ghl_GreenhillCoLlcMember		 200,000us-gaap_DefinedContributionPlanCostRecognized
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= ghl_GreenhillCoLlcMember		 300,000us-gaap_DefinedContributionPlanCostRecognized
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= ghl_GreenhillCoLlcMember
Contributions due to Retirement Plan included in compensation payable 200,000us-gaap_PensionAndOtherPostretirementAndPostemploymentBenefitPlansLiabilitiesCurrentAndNoncurrent
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= ghl_GreenhillCoLlcMember		 200,000us-gaap_PensionAndOtherPostretirementAndPostemploymentBenefitPlansLiabilitiesCurrentAndNoncurrent
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= ghl_GreenhillCoLlcMember		  
Greenhill And Company International LLC      
Defined Contribution Plan Disclosure [Line Items]      
Contributions due to Retirement Plan included in compensation payable 0us-gaap_PensionAndOtherPostretirementAndPostemploymentBenefitPlansLiabilitiesCurrentAndNoncurrent
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= ghl_GreenhillAndCompanyInternationalLLCMember		 0us-gaap_PensionAndOtherPostretirementAndPostemploymentBenefitPlansLiabilitiesCurrentAndNoncurrent
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= ghl_GreenhillAndCompanyInternationalLLCMember		  
Costs incurred for pension 600,000us-gaap_PensionExpense
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= ghl_GreenhillAndCompanyInternationalLLCMember		 600,000us-gaap_PensionExpense
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= ghl_GreenhillAndCompanyInternationalLLCMember		 700,000us-gaap_PensionExpense
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= ghl_GreenhillAndCompanyInternationalLLCMember
Greenhill & Co. Australia Pty Limited      
Defined Contribution Plan Disclosure [Line Items]      
Contributions due to Retirement Plan included in compensation payable 0us-gaap_PensionAndOtherPostretirementAndPostemploymentBenefitPlansLiabilitiesCurrentAndNoncurrent
/ us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis
= ghl_GreenhillCoAustraliaPtyLimitedMember		 0us-gaap_PensionAndOtherPostretirementAndPostemploymentBenefitPlansLiabilitiesCurrentAndNoncurrent
/ us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis
= ghl_GreenhillCoAustraliaPtyLimitedMember		  
Costs incurred for pension $ 500,000us-gaap_PensionExpense
/ us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis
= ghl_GreenhillCoAustraliaPtyLimitedMember		 $ 500,000us-gaap_PensionExpense
/ us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis
= ghl_GreenhillCoAustraliaPtyLimitedMember		 $ 600,000us-gaap_PensionExpense
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= ghl_GreenhillCoAustraliaPtyLimitedMember
Greenhill & Co. Australia Pty Limited | Pension Plan      
Defined Contribution Plan Disclosure [Line Items]      
Defined Contribution Plan Contribution Rates As Percentage Of Employees Earnings 9.00%ghl_DefinedContributionPlanContributionRatesAsPercentageOfEmployeesEarnings
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