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Related Parties - Additional Information (Detail) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Related Party Transaction [Line Items]      
Due to affiliates $ 0us-gaap_DueToRelatedPartiesCurrentAndNoncurrent $ 0us-gaap_DueToRelatedPartiesCurrentAndNoncurrent  
Sublease      
Related Party Transaction [Line Items]      
Rent reimbursements related to sublease 100,000us-gaap_TenantReimbursements
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= ghl_SubleaseMember		 100,000us-gaap_TenantReimbursements
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= ghl_SubleaseMember		 100,000us-gaap_TenantReimbursements
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= ghl_SubleaseMember
Payment for use of aircraft owned by executive $ 23,273us-gaap_AircraftRental
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= ghl_SubleaseMember		 $ 47,879us-gaap_AircraftRental
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= ghl_SubleaseMember		 $ 67,840us-gaap_AircraftRental
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= ghl_SubleaseMember