Segment Operating Results (Footnotes) (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Other Revenue, net		$ (422)	$ 206	$ (5,117)	$ (2,456)
Special Charges		28,000	3,732	33,499	3,732
Acquisition and Transition Costs		538	4,122	1,939	5,238
Other Expenses	[1]	58,213	8,910	116,773	16,525
Investment Banking [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	[2]	357	850	(2,874)	(731)
Interest expense on Senior Notes		1,452	1,134	4,889	3,344
Amortization of LP Units / Interests and Certain Other Awards		21,980	0	66,123	0
Other Acquisition Related Compensation Charges		0	592	1,537	6,371
Special Charges		0	3,732	2,151	3,732
Professional Fees Other Expenses		0	0	0	1,672
Acquisition and Transition Costs		538	4,122	1,928	4,122
Changes To Fair Value Of Contingent Consideration		2,797	0	2,797	0
Intangible Asset and Other Amortization		4,816	382	10,632	382
Other Expenses	[1]	30,131	8,828	85,168	16,279
Investment Management [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	[3]	(779)	(644)	(2,243)	(1,725)
Interest expense on Senior Notes		962	956	2,874	2,820
Special Charges		28,000	0	31,348	0
Acquisition and Transition Costs		0	0	11	0
Intangible Asset and Other Amortization		82	82	246	246
Other Expenses	[1]	$ 28,082	$ 82	$ 31,605	$ 246

[1] Other Expenses are as follows: For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014Investment Banking Amortization of LP Units / Interests and Certain Other Awards$21,980 $— $66,123 $—Other Acquisition Related Compensation Charges— 592 1,537 6,371Special Charges— 3,732 2,151 3,732Professional Fees— — — 1,672Acquisition and Transition Costs538 4,122 1,928 4,122Fair Value of Contingent Consideration2,797 — 2,797 —Intangible Asset and Other Amortization4,816 382 10,632 382Total Investment Banking30,131 8,828 85,168 16,279Investment Management Special Charges28,000 — 31,348 —Acquisition and Transition Costs— — 11 —Intangible Asset and Other Amortization82 82 246 246Total Investment Management28,082 82 31,605 246Total Other Expenses$58,213 $8,910 $116,773 $16,525

[2] Investment Banking Other Revenue, net, includes interest expense on the Senior Notes, subordinated borrowings and line of credit of $1,452 and $4,889 for the three and nine months ended September 30, 2015, respectively

[3] Investment Management Other Revenue, net, includes interest expense on the Senior Notes and line of credit of $962 and $2,874 for the three and nine months ended September 30, 2015, respectively