Segment Operating Results (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net Revenues	$ 350,656	$ 268,096	$ 608,369	$ 506,079
Operating Expenses	264,216	214,090	470,694	405,410
Other Expenses	23,835	22,895	58,945	58,560
Income Before Income from Equity Method Investments and Income Taxes	62,605	31,111	78,730	42,109
Income from Equity Method Investments	1,664	1,998	2,951	3,105
Pre-Tax Income	64,269	33,109	81,681	45,214
Identifiable Segment Assets	1,306,650	1,299,547	1,306,650	1,299,547	$ 1,479,171
Investment Banking [Member]
Segment Reporting Information [Line Items]
Net Revenues	328,157	244,377	567,870	460,957
Operating Expenses	246,916	194,271	439,180	365,635
Other Expenses	23,404	22,802	58,432	55,037
Income Before Income from Equity Method Investments and Income Taxes	57,837	27,304	70,258	40,285
Income from Equity Method Investments	290	803	18	766
Pre-Tax Income	58,127	28,107	70,276	41,051
Identifiable Segment Assets	964,009	848,750	964,009	848,750
Investment Management [Member]
Segment Reporting Information [Line Items]
Net Revenues	22,499	23,719	40,499	45,122
Operating Expenses	17,300	19,819	31,514	39,775
Other Expenses	431	93	513	3,523
Income Before Income from Equity Method Investments and Income Taxes	4,768	3,807	8,472	1,824
Income from Equity Method Investments	1,374	1,195	2,933	2,339
Pre-Tax Income	6,142	5,002	11,405	4,163
Identifiable Segment Assets	$ 342,641	$ 450,797	$ 342,641	$ 450,797