Debt Instrument, Amount Outstanding to Reduce Interest Rate

No definition available.

Name:	ghl_DebtInstrumentAmountOutstandingtoReduceInterestRate
Namespace Prefix:	ghl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Debt Instrument, Number of Semi-Annual Installments Payable

+ References

No definition available.

+ Details

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

- Definition

Number of loans payable

+ References

No definition available.

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Average amount borrowed under the credit facility during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityAverageOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of increase (decrease) of the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_LineOfCreditFacilityLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount of long-term loans payable classified as other.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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

- Definition

The cash outflow to settle a bank borrowing during the year.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3291-108585

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=ghl_Cogent12MonthFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ghl_Cogent36MonthFacilityMember
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Data Type:	na
Balance Type:
Period Type:

- Details

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- Details

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Balance Type:
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- Details

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- Details

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- Details

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- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LongTermDebtMember
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- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
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Bank Loan Facilities - Additional Information (Details)					1 Months Ended		3 Months Ended
Bank Loan Facilities - Additional Information (Details)	Apr. 30, 2018 USD ($)	Oct. 31, 2017 USD ($)	Apr. 10, 2017 USD ($)	Apr. 30, 2015 USD ($) Loan installment	Apr. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Feb. 28, 2017 USD ($)	Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Term loan facility						$ 16,875,000	$ 16,875,000			$ 16,875,000
Repayment of bank term loans							$ 0	$ 0
Cogent 12 Month Facility
Line of Credit Facility [Line Items]
Interest rate, percent				4.00%
Weighted average interest rate (percent)						4.99%	4.99%	4.57%
Cogent 36 Month Facility
Line of Credit Facility [Line Items]
Interest rate, percent				4.00%
Weighted average interest rate (percent)				1.25%		4.99%	4.99%	4.57%
Term loan facility						$ 16,900,000	$ 16,900,000
Debt instrument term (years)				3 years
Number of semi-annual installments (installment) \| installment				4
Debt instrument, amount outstanding to reduce interest rate				$ 7,500,000
Cogent 36 Month Facility \| Scenario, Forecast
Line of Credit Facility [Line Items]
Repayment of bank term loans	$ 5,600,000	$ 5,600,000
Cogent 36 Month Facility \| Subsequent Event
Line of Credit Facility [Line Items]
Repayment of bank term loans			$ 5,600,000		$ 5,600,000
Cogent 36 Month Facility \| Prime Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)				0.75%
Cogent Partners, LP
Line of Credit Facility [Line Items]
Term loan facility				$ 45,000,000
Number of bank term loan facilities (loan) \| Loan				2
Cogent Partners, LP \| Cogent 12 Month Facility \| Short-term Debt
Line of Credit Facility [Line Items]
Term loan facility				$ 22,500,000
Cogent Partners, LP \| Cogent 36 Month Facility \| Long-term Debt
Line of Credit Facility [Line Items]
Term loan facility				$ 22,500,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving loan facility, maximum borrowing capacity						80,000,000	$ 80,000,000		$ 70,000,000
Increase in maximum borrowing capacity						$ 10,000,000
Interest rate, percent						3.50%	3.50%
Weighted average daily borrowings outstanding under the loan facility							$ 63,700,000	$ 40,300,000
Weighted average interest rate (percent)						3.76%	3.76%	3.50%