Investments - Additional Information (Detail) (USD $)	3 Months Ended									3 Months Ended						12 Months Ended	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 GCP II [Member]	Dec. 31, 2012 GCP II [Member]	Mar. 31, 2013 GCP I [Member]	Dec. 31, 2012 GCP I [Member]	Mar. 31, 2013 Barrow Street III	May 30, 2005 Barrow Street III	Mar. 31, 2013 Merchant Banking Profit Overrides	Mar. 31, 2012 Merchant Banking Profit Overrides	Dec. 31, 2012 Merchant Banking Profit Overrides	Mar. 31, 2013 GCP III [Member]	Dec. 31, 2012 GCP III [Member]	Nov. 05, 2010 GCP III [Member]	Dec. 31, 2009 Nonsoftware License Arrangement [Member]	Mar. 31, 2013 Iridium [Member]	Mar. 31, 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
Investment related to noncontrolling interests				$ 900,000	$ 1,100,000	$ 300,000	$ 300,000
Other commitment									5,000,000						5,000,000
Unfunded commitments								100,000					3,400,000
Compensation payable	10,795,000		21,419,000							300,000		300,000
Percentage for each of the funds commitment amount that may be drawn for follow-on investments (percent)													15.00%
Investment in Iridium (shares)																	4,244,016		5,084,016
Share price (usd per share)																	$ 6.03
The percentage of ownership interestests which is fully diluted (percent)																	6.00%		7.00%
Net realized and unrealized gains (losses)	(2,081,000)	6,356,000								0	0						(2,081,000)	8,300,000
Investments in merchant banking funds	16,586,000		16,772,000			2,246,000	2,247,000						1,367,000	1,367,000
Fund commitments, expiration								2015
Commitment Expiry Month And Year													2016-11
Deferred gain on sale of certain merchant banking assets	$ 49,000	$ 65,000