Regulatory Requirements - Additional Information (Details)	6 Months Ended
Jun. 30, 2019 USD ($)
Broker-Dealer, Net Capital Requirement, SEC Regulation [Abstract]
Minimum net capital required	$ 5,000
Net capital	22,600,000
Excess net capital	$ 21,000,000
Aggregate indebtedness to net capital ratio (percent)	1.1
Description of minimum net capital requirements	The greater of $5,000 or 1/15 of aggregate indebtedness
Minimum capital requirements, portion of aggregate indebtedness	6.67%

Minimum Net Capital Requirement for Broker-Dealer Subsidiary, Percent

No definition available.

Name:	ghl_MinimumNetCapitalRequirementforBrokerDealerSubsidiaryPercent
Namespace Prefix:	ghl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of net capital in excess of minimum required net capital, calculated under Aggregate Indebtedness Standard.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher SEC
-Name Rule 15c3-1
-Number 240
-Section 15c3-1

+ Details

Name:	srt_ExcessNetCapitalAt1500Percent
Namespace Prefix:	srt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum amount of net capital required to be maintained by broker-dealer subsidiary to engage in security transaction, calculated under Aggregate Indebtedness Standard.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher SEC
-Name Rule 15c3-1
-Number 240
-Section 15c3-1

+ Details

Name:	srt_MinimumNetCapitalRequiredForBrokerDealerSubsidiary1
Namespace Prefix:	srt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of net capital of broker-dealer.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher SEC
-Name Rule 15c3-1
-Number 240
-Section 15c3-1

+ Details

Name:	srt_NetCapital
Namespace Prefix:	srt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	srt_RegulatoryCapitalRequirementsAbstract
Namespace Prefix:	srt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of the regulatory requirements for capital adequacy purposes.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=d3e65071-112826

+ Details

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

- Definition

Indebtedness divided by net capital.

+ References

No definition available.

+ Details

Name:	us-gaap_RatioOfIndebtednessToNetCapital1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant