Organization (Details)	Jun. 30, 2018 state
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of states in which the entity is licensed (state)	50

Number of States in which Entity is Licensed to Operate

No definition available.

Name:	ghl_NumberofStatesinwhichEntityisLicensedtoOperate
Namespace Prefix:	ghl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant