Amortization of deferred gain on sale of merchant banking assets

No definition available.

Name:	ghl_AmortizationOfDeferredGainOnSaleOfMerchantBankingAssets
Namespace Prefix:	ghl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Average Sales Price Per Share of Shares Sold

+ References

No definition available.

+ Details

Name:	ghl_AverageSalesPricePerShareOfSharesSold
Namespace Prefix:	ghl_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Gain (Loss) On Sale Of Business, Amortization Period of Gains (Losses)

+ References

No definition available.

+ Details

Name:	ghl_GainLossOnSaleOfBusinessAmortizationPeriodofGainsLosses
Namespace Prefix:	ghl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount to be paid on the repurchase date.

+ References

No definition available.

+ Details

Name:	ghl_InvestmentsRepurchaseAgreementAmountToBePaid
Namespace Prefix:	ghl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percent of Book Value of Investment Sold

+ References

No definition available.

+ Details

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

- Definition

Plan to Sell Common Shares, Duration

+ References

No definition available.

+ Details

Name:	ghl_PlantoSellCommonSharesDuration
Namespace Prefix:	ghl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares that has been sold during the period.

+ References

No definition available.

+ Details

Name:	ghl_SaleOfCommonStockShares
Namespace Prefix:	ghl_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the entity's equity method investment which has been sold.

+ References

No definition available.

+ Details

Name:	us-gaap_EquityMethodInvestmentSoldCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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

- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

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

- Definition

Total of all Partners' Capital (deficit) items which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 272

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 27

-Article 5

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 20

-Article 7

+ Details

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

- Definition

Amount of realized and unrealized gain (loss), from the firm's direct investment activity, conducted separately from customer trading activities, and includes, but is not limited to, investments in private equity, alternative investment products, real estate, and exchanges and memberships.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.13(g),(h))

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.2,3)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

+ Details

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

- Details

Name:	us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis=ghl_BarrowStreetCapitalIIILLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis=ghl_GcpIiiMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis=ghl_GcpIiMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis=ghl_GcpIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis=ghl_GreenhillCapitalPartnersEuropeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis=ghl_IridiumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Investments - Additional Information (Detail) (USD $)	12 Months Ended			6 Months Ended	1 Months Ended
Investments - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2012	Oct. 31, 2011
Fair Value, Measurement Inputs, Disclosure [Line Items]
Amortization period of gains	5 years
Deferred gain on sale of certain merchant banking assets	$ 195,000	$ 195,000	$ 260,000
GCP
Fair Value, Measurement Inputs, Disclosure [Line Items]
Sale of capital interests		2,000,000
GCPE
Fair Value, Measurement Inputs, Disclosure [Line Items]
Sale of capital interests			27,200,000
Book value of investment sold (percent)			90.00%
Merchant banking loss			(3,400,000)
GCP I
Fair Value, Measurement Inputs, Disclosure [Line Items]
Investment related to noncontrolling interests	100,000	100,000
GCP II
Fair Value, Measurement Inputs, Disclosure [Line Items]
Investments Repurchase Agreement Amount To Be Paid				15,600,000
Investment related to noncontrolling interests	600,000	900,000
Barrow Street III
Fair Value, Measurement Inputs, Disclosure [Line Items]
Other Commitment	$ 300,000
Iridium common stock
Fair Value, Measurement Inputs, Disclosure [Line Items]
Sale of common stock (shares)		5,084,016	3,850,000
Average price per share (usd per share)		$ 6.73	$ 7.91
Minimum \| Iridium common stock
Fair Value, Measurement Inputs, Disclosure [Line Items]
Duration of plan to sell common shares					2 years