Segment Operating Results (Footnotes) (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Other Revenue, net		$ (2,959)	$ (1,356)	$ (4,695)	$ (2,662)
Special Charges		(139)	0	5,499	0
Acquisition and Transition Costs		917	1,016	1,401	1,116
Other Expenses	[1]	22,895	4,319	58,560	7,615
Investment Banking [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	[2]	(2,173)	(928)	(3,231)	(1,581)
Interest expense on Senior Notes		1,793	1,105	3,437	2,210
Amortization of LP Units / Interests and Certain Other Awards		18,193	0	44,143	0
Other Acquisition Related Compensation Charges		952	2,565	1,537	5,779
Special Charges		(139)	0	2,151	0
Intangible Asset and Other Amortization		2,890	0	5,816	0
Professional Fees Other Expenses		0	1,672	0	1,672
Acquisition and Transition Costs		906	0	1,390	0
Other Expenses	[1]	22,802	4,237	55,037	7,451
Investment Management [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	[3]	(786)	(428)	(1,464)	(1,081)
Interest expense on Senior Notes		959	932	1,912	1,864
Special Charges		0	0	3,348	0
Intangible Asset and Other Amortization		82	82	164	164
Acquisition and Transition Costs		11	0	11	0
Other Expenses	[1]	$ 93	$ 82	$ 3,523	$ 164

[1] Other Expenses are as follows: For the Three Months Ended June 30, For the Six Months Ended June 30, 2015 2014 2015 2014Investment Banking Amortization of LP Units / Interests and Certain Other Awards$18,193 $— $44,143 $—Other Acquisition Related Compensation Charges952 2,565 1,537 5,779Special Charges(139) — 2,151 —Intangible Asset and Other Amortization2,890 — 5,816 —Professional Fees— 1,672 — 1,672Acquisition and Transition Costs906 — 1,390 —Total Investment Banking22,802 4,237 55,037 7,451Investment Management Special Charges— — 3,348 —Acquisition and Transition Costs11 — 11 —Intangible Asset and Other Amortization82 82 164 164Total Investment Management93 82 3,523 164Total Other Expenses$22,895 $4,319 $58,560 $7,615

[2] Investment Banking Other Revenue, net, includes interest expense on the Senior Notes, subordinated borrowings and line of credit of $1,793 and $3,437 for the three and six months ended June 30, 2015, respectively

[3] Investment Management Other Revenue, net, includes interest expense on the Senior Notes and line of credit of $959 and $1,912 for the three and six months ended June 30, 2015, respectively