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Business Information - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Segment
sources
Mar. 31, 2014
Segment Reporting Information    
Number of principal sources of revenue (source of revenue) 2us-gaap_NumberOfOperatingSegments  
Number of reportable segments (segments) 1us-gaap_NumberOfReportableSegments  
Advisory revenues $ 61,892us-gaap_InvestmentBankingRevenue $ 48,455us-gaap_InvestmentBankingRevenue
Investment revenues (losses) (9)ghl_InvestmentRevenues (4,886)ghl_InvestmentRevenues
Revenues as a percentage of total revenue (percent) 100.00%ghl_PercentageOfTotalRevenue 100.00%ghl_PercentageOfTotalRevenue
Total revenues $ 61,883us-gaap_Revenues $ 43,569us-gaap_Revenues
Advisory revenues    
Segment Reporting Information    
Revenues as a percentage of total revenue (percent) 100.00%ghl_PercentageOfTotalRevenue
/ us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis
= ghl_AdvisoryServicesMember
111.00%ghl_PercentageOfTotalRevenue
/ us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis
= ghl_AdvisoryServicesMember
Investment Revenues    
Segment Reporting Information    
Revenues as a percentage of total revenue (percent) 0.00%ghl_PercentageOfTotalRevenue
/ us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis
= ghl_InvestmentRevenuesMember
(11.00%)ghl_PercentageOfTotalRevenue
/ us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis
= ghl_InvestmentRevenuesMember