Segment Operating Results (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Segment Reporting Information [Line Items]
Net Revenues	$ 207,446	[1]	$ 172,497	[1]	$ 358,868	[1]	$ 275,295	[1]
Operating Expenses	159,332		138,748		285,205		236,974
Other Expenses	10,052	[2]	12,554	[2]	20,657	[2]	29,269	[2]
Operating Income (Loss)	38,062		21,195		53,006		9,052
Income (Loss) from Equity Method Investments	1,015		719		1,771		3,104
Pre-Tax Income (Loss)	39,077		21,914		54,777		12,156
Identifiable Segment Assets	1,032,963		973,858		1,032,963		973,858		1,145,218
Investment Banking [Member]
Segment Reporting Information [Line Items]
Net Revenues	182,605	[1]	153,164	[1]	314,201	[1]	236,949	[1]
Operating Expenses	138,389		118,683		243,455		197,659
Other Expenses	9,456	[2]	11,898	[2]	19,311	[2]	28,005	[2]
Operating Income (Loss)	34,760		22,583		51,435		11,285
Income (Loss) from Equity Method Investments	290		(33)		460		1,595
Pre-Tax Income (Loss)	35,050		22,550		51,895		12,880
Identifiable Segment Assets	562,690		486,481		562,690		486,481
Investment Management [Member]
Segment Reporting Information [Line Items]
Net Revenues	24,841	[1]	19,333	[1]	44,667	[1]	38,346	[1]
Operating Expenses	20,943		20,065		41,750		39,315
Other Expenses	596	[2]	656	[2]	1,346	[2]	1,264	[2]
Operating Income (Loss)	3,302		(1,388)		1,571		(2,233)
Income (Loss) from Equity Method Investments	725		752		1,311		1,509
Pre-Tax Income (Loss)	4,027		(636)		2,882		(724)
Identifiable Segment Assets	$ 470,273		$ 487,377		$ 470,273		$ 487,377

[1] Net revenues include Other Revenue, net, allocated to the segments as follows: For the Three Months Ended June 30, For the Six Months Ended June 30, 2013 2012 2013 2012Investment Banking (A)$(849) $(1,262) $(636) $(1,972)Investment Management (B)(897) (703) (2,610) (1,454)Total Other Revenue, net$(1,746) $(1,965) $(3,246) $(3,426) (A)Investment Banking Other Revenue, net, includes interest expense on the Senior Notes of $1,095 and $2,183 for the three and six months ended June 30, 2013, respectively, and $1,075 and $2,145 for the three and six months ended June 30, 2012, respectively.(B)Investment Management Other Revenue, net, includes interest expense on the Senior Notes of $924 and $1,843 for the three and six months ended June 30, 2013, respectively, and $909 and $1,813 for the three and six months ended June 30, 2012, respectively.

[2] Other Expenses are as follows: For the Three Months Ended June 30, For the Six Months Ended June 30, 2013 2012 2013 2012Investment Banking Amortization of LP Units and Certain Other Awards$4,300 $4,495 $9,209 $8,711Acquisition Related Compensation Charges5,156 6,352 10,102 15,997Special Charges— 662 — 662Intangible Asset Amortization— 389 — 2,635Total Investment Banking9,456 11,898 19,311 28,005Investment Management Amortization of LP Units and Certain Other Awards514 574 1,182 1,100Intangible Asset Amortization82 82 164 164Total Investment Management596 656 1,346 1,264Total Other Expenses$10,052 $12,554 $20,657 $29,269