Investments - Additional Information (Detail) (USD $)	9 Months Ended			3 Months Ended		9 Months Ended						3 Months Ended		9 Months Ended								9 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Merchant Banking Funds	Sep. 30, 2012 Merchant Banking Funds	Sep. 30, 2013 Merchant Banking Funds	Sep. 30, 2012 Merchant Banking Funds	Sep. 30, 2013 GCP II [Member]	Dec. 31, 2012 GCP II [Member]	Sep. 30, 2013 GCP I [Member]	Dec. 31, 2012 GCP I [Member]	Sep. 30, 2013 Merchant Banking Profit Overrides	Sep. 30, 2012 Merchant Banking Profit Overrides	Sep. 30, 2013 Merchant Banking Profit Overrides	Sep. 30, 2012 Merchant Banking Profit Overrides	Dec. 31, 2012 Merchant Banking Profit Overrides	Sep. 30, 2013 GCP III [Member]	Jul. 31, 2013 GCP III [Member]	Dec. 31, 2012 GCP III [Member]	Sep. 30, 2013 Barrow Street III	Dec. 31, 2005 Barrow Street III	Sep. 30, 2013 Nonsoftware License Arrangement [Member]	Sep. 30, 2013 Iridium [Member]	Sep. 30, 2012 Iridium [Member]	Sep. 30, 2013 Iridium [Member]	Sep. 30, 2012 Iridium [Member]	Dec. 31, 2012 Iridium [Member]
Fair Value, Measurement Inputs, Disclosure [Line Items]
Investments in merchant banking funds	$ 11,285,000		$ 16,772,000					$ 7,627,000	$ 11,173,000	$ 1,732,000	$ 2,247,000						$ 0	$ 2,000,000	$ 1,367,000
Non-compete and trademark licensing agreements amortization period																						5 years
Investment related to noncontrolling interests								900,000	1,100,000	100,000	300,000
Compensation payable	4,600,000		21,419,000									300,000		300,000		300,000
Gain (Loss) on Investments	(1,612,000)	100,000		394,000	161,000	(2,959,000)	1,253,000					0	0	0	0								(3,223,000)	(10,826,000)	1,347,000	(1,153,000)
Other commitment																					5,000,000
Unfunded commitments																				$ 100,000
Investment in Iridium (shares)																							1,595,629		1,595,629		5,084,016
Share price (usd per share)																							$ 6.88		$ 6.88		$ 6.72
The percentage of ownership interestests which is fully diluted (percent)																							2.00%		2.00%		7.00%
Fund commitments, expiration																				2015