Reasonable Representation of Each Segment's Contribution (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Segment Reporting Information [Line Items]
Net Revenues	$ 214,049	$ 153,029	$ 172,497	$ 102,798	$ 112,781	$ 163,181	$ 141,204	$ 107,098	$ 642,373	[1]	$ 524,264	[1]	$ 375,905	[1]
Operating Income	42,238	14,245	21,195	(12,143)	(1,009)	13,442	11,615	11,764	65,535		35,812		36,860
Income (Loss) from Equity Method Investments	1,333	415	719	2,385	255	195	69	400	4,852		919		(557)
Pre-Tax Income (Loss) from Continuing Operations	43,571	14,660	21,914	(9,758)	(754)	13,637	11,684	12,164	70,387		36,731		36,303
Identifiable Segment Assets	1,145,218				1,043,592				1,145,218		1,043,592		898,085
Operating Expenses									523,386		427,155		316,016
Other Expenses									53,452	[2]	61,297	[2]	23,029	[2]
Investment Banking
Segment Reporting Information [Line Items]
Net Revenues									565,219	[1]	428,124	[1]	301,847	[1]
Operating Expenses									444,510		337,886		240,312
Other Expenses									50,774	[2]	55,591	[2]	19,408	[2]
Operating Income									69,935		34,647		42,127
Income (Loss) from Equity Method Investments									2,258		1,101		16
Pre-Tax Income (Loss) from Continuing Operations									72,193		35,748		42,143
Identifiable Segment Assets	624,977				530,008				624,977		530,008		370,329
Investment Management
Segment Reporting Information [Line Items]
Net Revenues									77,154	[1]	96,140	[1]	74,058	[1]
Operating Income									(4,400)		1,165		(5,267)
Income (Loss) from Equity Method Investments									2,594		(182)		(573)
Pre-Tax Income (Loss) from Continuing Operations									(1,806)		983		(5,840)
Identifiable Segment Assets	520,241				513,584				520,241		513,584		527,756
Operating Expenses									78,876		89,269		75,704
Other Expenses									$ 2,678	[2]	$ 5,706	[2]	$ 3,621	[2]

[1] Net revenues include Other Revenue, net, allocated to the segments as follows: For the Years Ended December 31, 2012 2011 2010 Investment Banking(A) $ (3,019 ) $ (2,473 ) $ (84 ) Investment Management(B) (2,636 ) (3,021 ) (552 ) Total Other Revenue, net $ (5,655 ) $ (5,494 ) $ (636 )

[2] Other Expenses are as follows: For the Years Ended December 31, 2012 2011 2010 Investment Banking Amortization of LP Units and Certain Other Awards $ 18,601 $ 21,328 $ 17,532 Vesting of Event-based Awards - 8,906 - Acquisition Related Compensation Charges 28,163 14,618 - Special Charges 662 3,894 - Intangible Asset Amortization 3,348 6,845 1,876 Total Investment Banking 50,774 55,591 19,408 Investment Management Amortization of LP Units and Certain Other Awards 2,350 2,892 3,289 Vesting of Event-based Awards - 2,483 - Intangible Asset Amortization 328 331 332 Total Investment Management 2,678 5,706 3,621 Total Other Expenses $ 53,452 $ 61,297 $ 23,029