Investments as a Percent of Revenue

No definition available.

Name:	ghl_InvestmentsasaPercentofRevenue
Namespace Prefix:	ghl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Clients With Greater Than Ten Percent Revenue

+ References

No definition available.

+ Details

Name:	ghl_NumberOfClientsWithGreaterThanTenPercentRevenue
Namespace Prefix:	ghl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Long-lived assets other than financial instruments, long-term customer relationships of a financial institution, mortgage and other servicing rights, deferred policy acquisition costs, and deferred tax assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e9038-108599

+ Details

Name:	us-gaap_NoncurrentAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementGeographicalAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_SalesRevenueNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_GeographicConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=country_GB
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PrincipleTransactionRevenueDescriptionOfReportingCategoryAxis=ghl_AdvisoryServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Business Information - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Segment Entity	Dec. 31, 2016 USD ($) Entity	Dec. 31, 2015
Segment Reporting Information [Line Items]
Number of business segments (segment) \| Segment	1
United States
Segment Reporting Information [Line Items]
Long-lived assets \| $	$ 36.6	$ 34.8
Revenue
Segment Reporting Information [Line Items]
Percentage of revenues from investments (less than)	1.00%
Revenue \| Geographic Concentration Risk \| United States
Segment Reporting Information [Line Items]
Percent of revenue per derived location	70.00%	59.00%	66.00%
Revenue \| Geographic Concentration Risk \| United Kingdom
Segment Reporting Information [Line Items]
Percent of revenue per derived location	15.00%	27.00%	20.00%
Advisory Services
Segment Reporting Information [Line Items]
Number of clients that accounted for more than 10% of total revenues (entity) \| Entity	0	0