Investments - Additional Information (Detail) (USD $)	12 Months Ended								1 Months Ended			12 Months Ended		1 Months Ended	3 Months Ended	12 Months Ended				12 Months Ended		12 Months Ended				1 Months Ended	12 Months Ended			27 Months Ended			1 Months Ended	12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2009 Nonsoftware License Arrangement	Dec. 31, 2009 Greenhill Capital Partners II LLC [Member]	Dec. 31, 2012 GCP I [Member]	Dec. 31, 2011 GCP I [Member]	Jun. 30, 2011 GCP II LLC	Dec. 31, 2012 GCP II LLC	Dec. 31, 2011 GCP II LLC	Dec. 31, 2012 GCP II LLC Put Option	Dec. 31, 2011 GCP II LLC Put Option	Jun. 30, 2012 GCP II LLC Future Period	Sep. 30, 2012 GCP II LLC Future Period	Dec. 31, 2011 GCP II LLC Future Period	Dec. 31, 2012 GCP III [Member]	Dec. 31, 2011 GCP III [Member]	Nov. 30, 2010 GCP III [Member]	Dec. 31, 2012 GCPE	Dec. 31, 2011 GCPE	Dec. 31, 2011 GSAVP	Dec. 31, 2012 Merchant Banking Profit Overrides	Dec. 31, 2011 Merchant Banking Profit Overrides	Dec. 31, 2010 Merchant Banking Profit Overrides	Jun. 30, 2011 Iridium	Dec. 31, 2012 Iridium	Dec. 31, 2011 Iridium	Dec. 31, 2010 Iridium	Dec. 31, 2013 Iridium	Dec. 31, 2012 Iridium Common Stock	Dec. 31, 2011 Iridium Common Stock	Jun. 30, 2011 Iridium Warrant	Dec. 31, 2012 Iridium Significant Unobservable Inputs (Level 3) Warrant	Dec. 31, 2011 Iridium Significant Unobservable Inputs (Level 3) Warrant	Dec. 31, 2012 Barrow Street III	May 30, 2005 Barrow Street III	Dec. 31, 2011 GCP Capital Partners Holdings LLC [Member]	Dec. 31, 2010 GCP Capital Partners Holdings LLC [Member]	Dec. 31, 2010 GCP Capital Partners Holdings LLC [Member] Maximum
Fair Value, Measurement Inputs, Disclosure [Line Items]
Net realized and unrealized gains (losses)	$ (8,401,000)	$ (13,954,000)	$ 11,724,000																				$ 0	$ 0	$ 188,000		$ (4,980,000)	$ (6,184,000)	$ 5,044,000
Percentage ownership sold to GCP Capital						24.00%
Retained ownership interest						76.00%
Shares received as consideration for sale of the merchant banking business				289,050
Consideration received from sale of the merchant banking business				24,400,000
Sale of the merchant banking business, recognized gain				21,800,000
Deferred Gain on sale related to non-compete and trademark licensing agreements				2,600,000
Non-compete and trademark licensing agreements amortization period					5 years
Amortization Of Deferred Gain On Sale Of Merchant Banking Assets	260,000	811,000	1,100,000
Amount of profit threshold allocable to GCP Capital																																								10,000,000
Sale of capital interests									44,800,000											27,200,000		4,600,000
Put option														1,300,000	15,600,000	14,300,000
Merchant banking gains/losses												(2,000,000)	(3,800,000)							(3,400,000)
Investments in merchant banking funds	16,772,000	41,642,000					2,247,000	2,552,000		9,700,000							1,367,000	903,000		0	23,951,000
Investment related to noncontrolling interests							300,000	300,000		1,100,000	1,100,000
Other Commitment																			5,000,000																		5,000,000
Fund commitments, expiration																																				2013
Net income (loss) allocated to noncontrolling interests	0	6,000	4,895,000																																			4,900,000
Distributions to noncontrolling interests	0																																					1,000,000	4,200,000
Compensation payable	21,419,000	34,913,000																					300,000	300,000
Commitment Expiry Month And Year																	2016-11
Percentage for each of the funds commitment amount that may be drawn for follow-on investments																	15.00%
Unfunded commitments																	3,400,000																			100,000
Management fees	$ 0	$ 0	$ 12,857,000
Investment in Iridium																															5,084,016	8,934,016
Share Price																											$ 6.72
The percentage of ownership interestests which is fully diluted																											7.00%	12.00%
12b-1 Sale Plan - Years																														2 years
Number of warrants tendered in exchange shares of Common Stock																											4,000,000
Number of shares exchanged for tendered warrants																											880,000
Number of shares sold																											3,850,000	870,000
Average price per share																											$ 7.91	$ 6.72
Warrants exercise price																										$ 11.50							$ 11.50	$ 11.50	$ 11.50
Percent of Book Value of Investment Sold																				90.00%