Investments - Additional Information (Detail) (USD $)	6 Months Ended			3 Months Ended		6 Months Ended						3 Months Ended		6 Months Ended								12 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Merchant Banking Funds	Jun. 30, 2012 Merchant Banking Funds	Jun. 30, 2013 Merchant Banking Funds	Jun. 30, 2012 Merchant Banking Funds	Jun. 30, 2013 GCP II [Member]	Dec. 31, 2012 GCP II [Member]	Jun. 30, 2013 GCP I [Member]	Dec. 31, 2012 GCP I [Member]	Jun. 30, 2013 Merchant Banking Profit Overrides	Jun. 30, 2012 Merchant Banking Profit Overrides	Jun. 30, 2013 Merchant Banking Profit Overrides	Jun. 30, 2012 Merchant Banking Profit Overrides	Dec. 31, 2012 Merchant Banking Profit Overrides	Jun. 30, 2013 GCP III [Member]	Dec. 31, 2012 GCP III [Member]	Nov. 05, 2010 GCP III [Member]	Jun. 30, 2013 Barrow Street III	Dec. 31, 2005 Barrow Street III	Dec. 31, 2009 Nonsoftware License Arrangement [Member]	Jun. 30, 2013 Iridium [Member]	Jun. 30, 2012 Iridium [Member]	Jun. 30, 2013 Iridium [Member]	Jun. 30, 2012 Iridium [Member]	Dec. 31, 2012 Iridium [Member]
Fair Value, Measurement Inputs, Disclosure [Line Items]
Non-compete and trademark licensing agreements amortization period																						5 years
Deferred gain on sale of certain merchant banking assets				$ 49,000	$ 65,000	$ 98,000	$ 129,000
Investment related to noncontrolling interests								900,000	1,100,000	100,000	300,000
Compensation payable	15,337,000		21,419,000									300,000		300,000		300,000
Gain (Loss) on Investments	1,217,000	8,134,000		(3,354,000)	388,000	(3,354,000)	1,092,000					0	0	0	0								6,652,000	1,372,000	4,570,000	9,674,000
Other commitment																			5,000,000		5,000,000
Unfunded commitments																	2,900,000			100,000
Investment in Iridium (shares)																							3,359,016		3,359,016		5,084,016
Share price (usd per share)																							$ 7.76		$ 7.76		$ 6.72
The percentage of ownership interestests which is fully diluted (percent)																							4.00%		4.00%		7.00%
Investments in merchant banking funds	$ 12,997,000		$ 16,772,000					$ 7,516,000	$ 11,173,000	$ 1,587,000	$ 2,247,000						$ 2,025,000	$ 1,367,000
Fund commitments, expiration																				2015