Debt Instrument, Amount Outstanding to Reduce Interest Rate

No definition available.

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

- Definition

Debt Instrument, Number of Repayment Installments

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Line Of Credit Facility, Annual Prepayment of Principal, Period of Time Required before Year End

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Line Of Credit Facility, Annual Principal Payment, Percentage Of Excess Cash Flow

+ References

No definition available.

+ Details

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- Definition

Line Of Credit Facility, Collateral, Capital Stock Of Subsidiary, Percentage

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Line Of Credit Facility, Covenant, Leverage Ratio, Excess Borrowings, Minimum

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Number of loans payable

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Amount of amortization expense attributable to debt discount (premium) and debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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Period Type:	duration

- 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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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

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
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Balance Type:	na
Period Type:	duration

- 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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Balance Type:	na
Period Type:	duration

- Definition

Amount, after accumulated amortization, of debt discount.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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-Subparagraph (SX 210.5-02.17)
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Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of the total principal payments made during the annual reporting period.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Average amount borrowed under the credit facility during the period.

+ References

No definition available.

+ 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 the required periodic payment applied to principal.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Weighted average interest rate of long-term debt outstanding calculated over time.

+ References

No definition available.

+ Details

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

- Definition

Amount of long-term loans payable classified as other.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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Period Type:	instant

- Definition

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
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- Definition

The cash outflow for the settlement of obligation drawn from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

+ References

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Loan Facilities - Additional Information (Detail)		1 Months Ended				3 Months Ended	6 Months Ended	12 Months Ended				45 Months Ended
Loan Facilities - Additional Information (Detail)	Oct. 12, 2017 USD ($)	Oct. 31, 2017 USD ($)	Apr. 30, 2016 installment	Jun. 30, 2015 installment	Apr. 30, 2015 USD ($) Loan installment	Dec. 31, 2017 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2022 USD ($)	Apr. 01, 2015 USD ($) Loan
Line of Credit Facility [Line Items]
Debt, discount						$ 1,663,000			$ 1,663,000	$ 0
Deferred financing costs						9,289,000			9,289,000	0
Bank term loans payable						$ 0			0	16,875,000
Repayments of bank term loans									$ 16,875,000	$ 16,875,000	$ 11,250,000
Cogent Partners, LP
Line of Credit Facility [Line Items]
Bank term loans payable					$ 45,000,000								$ 45,000,000
Number of bank term loan facilities (loan) \| Loan					2								2
Revolving credit facility
Line of Credit Facility [Line Items]
Weighted average interest rate						4.10%			4.10%	3.50%	3.30%
Amount repaid		$ 83,800,000
Interest rate						3.50%			3.50%
Weighted average daily borrowings outstanding under the loan facility									$ 65,300,000	$ 54,100,000
Revolving credit facility \| U.S. Prime Rate
Line of Credit Facility [Line Items]
Spread on interest rate									4.25%
Recapitalization credit agreement \| Secured debt
Line of Credit Facility [Line Items]
Incurred expenses related to issuance of debt	$ 11,500,000
Debt, discount	1,750,000
Deferred financing costs	$ 9,800,000
Incremental expense related to the amortization of debt issuance costs						$ 600,000
Recapitalization credit agreement \| Secured debt \| United States
Line of Credit Facility [Line Items]
Collateral percentage, capital stock of subsidiary	100.00%
Recapitalization credit agreement \| Secured debt \| Non-US
Line of Credit Facility [Line Items]
Collateral percentage, capital stock of subsidiary	65.00%
Recapitalization credit agreement \| Secured debt \| Base rate
Line of Credit Facility [Line Items]
Spread on interest rate	2.75%
Recapitalization credit agreement \| Secured debt \| LIBOR
Line of Credit Facility [Line Items]
Spread on interest rate	3.75%
Recapitalization credit agreement \| Secured debt \| Term loan
Line of Credit Facility [Line Items]
Face amount of debt		$ 350,000,000
Percentage of redemption price	101.00%
Recapitalization credit agreement \| Secured debt \| Term loan \| Forecast
Line of Credit Facility [Line Items]
Principal payments							$ 4,375,000					$ 8,750,000
Annual principal payments												$ 35,000,000
Period of time required before year end to make annual prepayments of principal								90 days
Annual prepayment of principal, percentage amount of annual excess cash flow								50.00%
Recapitalization credit agreement \| Secured debt \| Revolving credit facility
Line of Credit Facility [Line Items]
Covenant, leverage ratio, excess borrowings, minimum	$ 12,500,000.0
Term Loan Facility \| Secured debt \| Term loan
Line of Credit Facility [Line Items]
Face amount of debt	$ 350,000,000
Debt term	5 years
Long-term Debt, Weighted Average Interest Rate, over Time	5.10%
Amounts outstanding on lines of credit						350,000,000			$ 350,000,000
Term Loan Facility \| Secured debt \| Term loan \| Minimum
Line of Credit Facility [Line Items]
Weighted average interest rate	5.00%
Term Loan Facility \| Secured debt \| Term loan \| Maximum
Line of Credit Facility [Line Items]
Weighted average interest rate	5.30%
Revolving Loan Facility \| Secured debt \| Revolving credit facility
Line of Credit Facility [Line Items]
Face amount of debt	$ 20,000,000
Debt term	3 years
Amounts outstanding on lines of credit						$ 0			$ 0
Cogent 12 Month Facility
Line of Credit Facility [Line Items]
Weighted average interest rate					0.75%	5.20%			5.20%	4.70%
Number of equal payment installments \| installment			1	1	2
Cogent 12 Month Facility \| Cogent Partners, LP \| Short-term debt
Line of Credit Facility [Line Items]
Bank term loans payable					$ 22,500,000								$ 22,500,000
Cogent 36 Month Facility
Line of Credit Facility [Line Items]
Weighted average interest rate					1.25%
Amount outstanding to reduce interest rate					$ 7,500,000
Repayments of bank term loans									$ 16,900,000	$ 5,625,000
Cogent 36 Month Facility \| U.S. Prime Rate
Line of Credit Facility [Line Items]
Spread on interest rate					0.75%