Leases - Operating lease,future rental payments, maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Leases [Abstract]
2021 (remainder)	$ 5,937	$ 11,671
2022	13,737	11,190
2023	11,882	10,171
2024	10,207	9,329
2025	9,038	8,756
Thereafter	76,877	76,875
Total lease payments	127,678	127,992
Less: minimum future rental payments for which the lease has not commenced	(1,109)	0
Total lease payments for which the Company has a right-of-use-asset and corresponding liability	126,569	127,992
Plus: tenant incentive allowance utilized to finance leasehold improvements	10,930	11,302
Less: Interest	(41,890)	(44,197)
Present value of operating lease liabilities	$ 95,609	$ 95,097

Lessee, Operating Lease, Lease Not yet Commenced, To Be Paid

No definition available.

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- Definition

Lessee, Operating Lease, Liability, Tenant Incentive, Leasehold Improvements

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Lessee, Operating Lease, Liability, to be Paid, After Year Four

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Lessee, Operating Lease, Right-Of-Use Asset And Corresponding Liability, To Be Paid

+ References

No definition available.

+ Details

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Namespace Prefix:	ghl_
Data Type:	xbrli:monetaryItemType
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- References

No definition available.

+ Details

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- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918701-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease having initial or remaining lease term in excess of one year to be paid in remainder of current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918701-209980

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payments in excess of discounted obligation for lease payments for operating lease.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977

+ Details

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Balance Type:	credit
Period Type:	instant