Segment Operating Results (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Segment Reporting Information [Line Items]
Net Revenues	$ 218,672	$ 187,328	$ 206,797	$ 152,631	$ 214,049	$ 153,029	$ 172,497	$ 102,798	$ 765,428	[1]	$ 642,373	[1]	$ 524,264	[1]
Operating Expenses									598,806		523,386		427,155
Other Expenses									36,447	[2]	53,452	[2]	61,297	[2]
Income (Loss) Before Income from Equity Method Investments and Income Taxes	43,876	31,868	38,181	16,250	42,238	14,245	21,195	(12,143)	130,175		65,535		35,812
Income from Equity Method Investments	5,993	562	1,015	756	1,333	415	719	2,385	8,326		4,852		919
Pre-Tax Income (Loss) from Continuing Operations	49,869	32,430	39,196	17,006	43,571	14,660	21,914	(9,758)	138,501		70,387		36,731
Identifiable Segment Assets	1,180,783				1,145,218				1,180,783		1,145,218		1,043,592
Investment Banking [Member]
Segment Reporting Information [Line Items]
Net Revenues									670,785	[1]	565,219	[1]	428,124	[1]
Operating Expenses									516,921		444,510		337,886
Other Expenses									33,740	[2]	50,774	[2]	55,591	[2]
Income (Loss) Before Income from Equity Method Investments and Income Taxes									120,124		69,935		34,647
Income from Equity Method Investments									2,906		2,258		1,101
Pre-Tax Income (Loss) from Continuing Operations									123,030		72,193		35,748
Identifiable Segment Assets	693,890				624,977				693,890		624,977		530,008
Investment Management [Member]
Segment Reporting Information [Line Items]
Net Revenues									94,643	[1]	77,154	[1]	96,140	[1]
Operating Expenses									81,885		78,876		89,269
Other Expenses									2,707	[2]	2,678	[2]	5,706	[2]
Income (Loss) Before Income from Equity Method Investments and Income Taxes									10,051		(4,400)		1,165
Income from Equity Method Investments									5,420		2,594		(182)
Pre-Tax Income (Loss) from Continuing Operations									15,471		(1,806)		983
Identifiable Segment Assets	$ 486,893				$ 520,241				$ 486,893		$ 520,241		$ 513,584

[1] Net revenues include Other Revenue, net, allocated to the segments as follows: For the Years Ended December 31, 2013 2012 2011Investment Banking (A)$3,979 $(3,019) $(2,473)Investment Management (B)(1,116) (2,636) (3,021)Total Other Revenue, net$2,863 $(5,655) $(5,494) (A)Investment Banking Other Revenue, net, includes interest expense on the Senior Notes of $4,386, $4,312 and $4,238 for the years ended December 31, 2013, 2012 and 2011, respectively, and changes in amounts due pursuant to the Company's tax receivable agreement of $5,524 for the year ended December 31, 2013.(B)Investment Management Other Revenue, net, includes interest expense on the Senior Notes of $3,702, $3,643 and $3,579 for the years ended December 31, 2013, 2012 and 2011, respectively, and changes in amounts due pursuant to the Company's tax receivable agreement of $1,381 for the year ended December 31, 2013.

[2] Other Expenses are as follows: For the Years Ended December 31, 2013 2012 2011Investment Banking Amortization of LP Units and Certain Other Awards$17,817 $18,601 $21,328Vesting of Event-based Awards— — 8,906Acquisition Related Compensation Charges15,923 28,163 14,618Special Charges— 662 3,894Intangible Asset Amortization— 3,348 6,845Total Investment Banking33,740 50,774 55,591Investment Management Amortization of LP Units and Certain Other Awards2,209 2,350 2,892Vesting of Event-based Awards— — 2,483Special Charges170 — —Intangible Asset Amortization328 328 331Total Investment Management2,707 2,678 5,706Total Other Expenses$36,447 $53,452 $61,297