Investments - Additional Information (Detail)	1 Months Ended	3 Months Ended		6 Months Ended			6 Months Ended		1 Months Ended			3 Months Ended		6 Months Ended	12 Months Ended								6 Months Ended			6 Months Ended		6 Months Ended		6 Months Ended
	Jun. 30, 2011 USD ($)	Jun. 30, 2012 USD ($)	Jun. 30, 2011 USD ($)	Jun. 30, 2012 USD ($)	Jun. 30, 2011 USD ($)	Dec. 31, 2011 USD ($)	Jun. 30, 2012 Caliburn Acquisition	Jun. 30, 2012 Maximum	Jun. 30, 2011 GCP II USD ($)	Jun. 30, 2012 GCP II USD ($)	Dec. 31, 2011 GCP II USD ($)	Jun. 30, 2012 GCP II Put Option USD ($)	Mar. 31, 2011 GCP II Put Option USD ($)	Jun. 30, 2012 GCP II Put Option USD ($)	Dec. 31, 2011 GCP II Put Option USD ($)	Jun. 30, 2012 GCP I USD ($)	Dec. 31, 2011 GCP I USD ($)	Jun. 30, 2012 Merchant Banking Profit Overrides USD ($)	Dec. 31, 2011 Merchant Banking Profit Overrides USD ($)	Jun. 30, 2012 GCP Europe USD ($)	Jun. 30, 2012 GCP Europe GBP (£)	Jun. 30, 2012 GCP III USD ($)	Jun. 30, 2012 Merchant Banking Funds	Jun. 30, 2012 Iridium	Dec. 31, 2011 Iridium	Jun. 30, 2012 Iridium Common Stock	Dec. 31, 2011 Iridium Common Stock	Jun. 30, 2012 Iridium Warrant	Jun. 30, 2011 Iridium Warrant	Jun. 30, 2012 Iridium Significant Unobservable Inputs (Level 3) Warrant USD ($)	Jun. 30, 2012 Barrow Street III USD ($)
Fair Value, Measurement Inputs, Disclosure [Line Items]
Sale of Capital Interest	$ 3,700,000								$ 44,800,000
Put option												15,600,000	14,300,000	15,600,000	14,300,000
Purchasers funded capital call												1,300,000		1,300,000
Merchant banking and other investment revenues		2,170,000	5,188,000	11,604,000	5,047,000							200,000		(700,000)
Investment related to non controlling interests										1,100,000	1,100,000					300,000	300,000
Compensation payable		9,477,000		9,477,000		34,913,000												300,000	300,000
Unfunded commitments		9,500,000		9,500,000																6,400,000	4,100,000	3,100,000									100,000
Unfunded commitments, expiry date																				2012-12	2012-12	2015-11
Percentage for each of the funds commitment amount that may be drawn for follow-on investments								15.00%
Period for each of Funds in which the commitment amount may be drawn for follow-on investments																							2 years
Investment in Iridium																										6,939,016	8,934,016
The percentage of ownership interests which is fully diluted																								9.00%	12.00%
Commitments																															$ 5,000,000
Fund commitments, expiration																															2013
Deferred compensation payments							Investments will be distributed to those employees of Greenhill Caliburn over a period ending in 2016.
Warrants to purchase additional shares, owned																													4,000,000
Warrants exchanged with common shares																												4,000,000
Warrants exercise price																														$ 11.50
Effective date the Company participated in Iridium's tender off to exchange the Iridum Warrants for shares of common stock				June 22, 2011
Warrant issue,exercise of company's common stock																										880,000