Segment Operating Results (Footnotes) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Segment Reporting Information [Line Items]
Other Revenue, net	$ (1,736)		$ (1,306)
Special Charges	5,638		0
Acquisition and Transition Costs	484		100
Other Expenses	35,665	[1]	3,296	[1]
Investment Banking [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	(1,058)	[2]	(653)	[2]
Interest expense on Senior Notes	1,644		1,105
Amortization of LP Units / Interests and Certain Other Awards	25,950		0
Other Acquisition Related Compensation Charges	585		3,214
Special Charges	2,290		0
Intangible Asset and Other Amortization	2,926		0
Acquisition and Transition Costs	484		0
Other Expenses	32,235	[1]	3,214	[1]
Investment Management [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	(678)	[3]	(653)	[3]
Interest expense on Senior Notes	953		932
Special Charges	3,348		0
Intangible Asset and Other Amortization	82		82
Other Expenses	$ 3,430	[1]	$ 82	[1]

[1] 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

[2] 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

[3] 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