Segment Operating Results (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Segment Reporting Information [Line Items]
Net Revenues	$ 237,983	[1]	$ 149,113	[1]
Operating Expenses	191,320		125,103
Other Expenses	35,665	[2]	3,296	[2]
Operating Income (Loss)	10,998		20,714
Income (Loss) from Equity Method Investments	1,107		241
Pre-Tax Income (Loss)	12,105		20,955
Identifiable Segment Assets	1,289,209		1,044,917		1,446,556
Investment Banking [Member]
Segment Reporting Information [Line Items]
Net Revenues	216,580	[1]	127,851	[1]
Operating Expenses	171,364		105,532
Other Expenses	32,235	[2]	3,214	[2]
Operating Income (Loss)	12,981		19,105
Income (Loss) from Equity Method Investments	(37)		(310)
Pre-Tax Income (Loss)	12,944		18,795
Identifiable Segment Assets	769,746		590,956
Investment Management [Member]
Segment Reporting Information [Line Items]
Net Revenues	21,403	[1]	21,262	[1]
Operating Expenses	19,956		19,571
Other Expenses	3,430	[2]	82	[2]
Operating Income (Loss)	(1,983)		1,609
Income (Loss) from Equity Method Investments	1,144		551
Pre-Tax Income (Loss)	(839)		2,160
Identifiable Segment Assets	$ 519,463		$ 453,961

[1] Net revenues include Other Revenue, net, allocated to the segments as follows: For the Three Months Ended March 31, 2015 2014Investment Banking (A)$(1,058) $(653)Investment Management (B)(678) (653)Total Other Revenue, net$(1,736) $(1,306)(A)Investment Banking Other Revenue, net, includes interest expense on the Senior Notes, subordinated borrowings and line of credit of $1,644 and $1,105 for the three months ended March 31, 2015 and 2014, respectively(B)Investment Management Other Revenue, net, includes interest expense on the Senior Notes, subordinated borrowings and line of credit of $953 and $932 for the three months ended March 31, 2015 and 2014, respectively

[2] Other Expenses are as follows: For the Three Months Ended March 31, 2015 2014Investment Banking Amortization of LP Units / Interests and Certain Other Awards$25,950 $—Other Acquisition Related Compensation Charges585 3,214Special Charges2,290 —Intangible Asset and Other Amortization2,926 —Acquisition and Transition Costs484 —Total Investment Banking32,235 3,214Investment Management Special Charges3,348 —Intangible Asset and Other Amortization82 82Total Investment Management3,430 82Total Other Expenses$35,665 $3,296