Concentrations Of Credit Risk (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Concentrations Of Credit Risk [Abstract]
Securities purchased under agreements to resell	$ 2,146	$ 126,401
Market value of collateral received	2,143	126,386
Securities sold under agreements to repurchase	129,577	178,683
Market value of collateral pledged	(129,809)	(178,603)
Total receivables	52,060	49,625
Bad debt expense	1,558	1,008	444
Investment banking and investment management receivables collection periods (in days)	90
Collection period for restructuring transactions and private equity fee receivables (in days)	90
Marketable Securities	$ 81,288	$ 92,830
Percentage of marketable securities related to corporate and municipal bonds and other debt securities	75.00%
Percentage of marketable securities related to seed capital investments and mutual funds	25.00%