Investments - Investment Revenues (Details) (USD $)	3 Months Ended						3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Iridium	Mar. 31, 2013 Iridium	Mar. 31, 2014 GCP I	Dec. 31, 2013 GCP I	Mar. 31, 2014 Merchant Banking Funds	Mar. 31, 2013 Merchant Banking Funds	Mar. 31, 2014 GCP II	Dec. 31, 2013 GCP II
Principal Transaction Revenue [Line Items]
Investment related to noncontrolling interests					$ 100,000	$ 100,000			$ 900,000	$ 900,000
Net realized and unrealized gains (losses)	(5,231,000)	(2,081,000)	0	(2,081,000)			(5,205,000)	0
Deferred gain on sale of certain merchant banking assets							49,000	49,000
Interest income	270,000	176,000
Total investment revenues (losses)	$ (4,886,000)	$ (1,856,000)