Segment Operating Results (Other Expenses) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Segment Reporting Information [Line Items]
Vesting of Event-based Awards							$ 11,467
Special Charges			2,626		662		2,626
Total Other Expenses	12,735	[1]	17,793	[1]	42,004	[1]	42,906	[1]
Investment Banking [Member]
Segment Reporting Information [Line Items]
Amortization of LP Units and Certain Other Awards	4,866		4,580		13,577		15,603
Vesting of Event-based Awards							8,906
Acquisition Related Compensation Charges	6,802		7,729		22,799		7,729
Special Charges			2,626		662		2,626
Intangible Asset Amortization	389		2,034		3,024		2,972
Total Investment Banking	12,057	[1]	16,969	[1]	40,062	[1]	37,836	[1]
Investment Management [Member]
Segment Reporting Information [Line Items]
Amortization of LP Units and Certain Other Awards	596		741		1,696		2,338
Vesting of Event-based Awards							2,483
Intangible Asset Amortization	82		83		246		249
Total Investment Management	$ 678	[1]	$ 824	[1]	$ 1,942	[1]	$ 5,070	[1]

[1] Other Expenses are as follows: For the Three Months Ended September 30, For the Nine Months Ended September 30, 2012 2011 2012 2011 Investment Banking Amortization of LP Units and Certain Other Awards $ 4,866 $ 4,580 $ 13,577 $ 15,603 Vesting of Event-based Awards - - - 8,906 Acquisition Related Compensation Charges 6,802 7,729 22,799 7,729 Special Charges - 2,626 662 2,626 Intangible Asset Amortization 389 2,034 3,024 2,972 Total Investment Banking 12,057 16,969 40,062 37,836 Investment Management Amortization of LP Units and Certain Other Awards 596 741 1,696 2,338 Vesting of Event-based Awards - - - 2,483 Intangible Asset Amortization 82 83 246 249 Total Investment Management 678 824 1,942 5,070 Total Other Expenses $ 12,735 $ 17,793 $ 42,004 $ 42,906