Segment Operating Results (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net Revenues	$ 370,470	$ 350,656	$ 757,717	$ 608,369
Operating Expenses	282,826	264,216	577,723	470,694
Other Expenses	41,378	23,835	22,399	58,945
Income Before Income from Equity Method Investments and Income Taxes	46,266	62,605	157,595	78,730
Income (Loss) from Equity Method Investments	2,070	1,664	3,680	2,951
Pre-Tax Income (Loss)	48,336	64,269	161,275	81,681
Identifiable Segment Assets	1,451,286	1,306,650	1,451,286	1,306,650	$ 1,662,346
Investment Banking [Member]
Segment Reporting Information [Line Items]
Net Revenues	356,409	328,157	727,179	567,870
Operating Expenses	269,717	246,916	551,309	439,180
Other Expenses	33,894	23,404	14,915	58,432
Income Before Income from Equity Method Investments and Income Taxes	52,798	57,837	160,955	70,258
Income (Loss) from Equity Method Investments	113	290	(36)	18
Pre-Tax Income (Loss)	52,911	58,127	160,919	70,276
Identifiable Segment Assets	1,135,094	964,009	1,135,094	964,009
Investment Management [Member]
Segment Reporting Information [Line Items]
Net Revenues	14,061	22,499	30,538	40,499
Operating Expenses	13,109	17,300	26,414	31,514
Other Expenses	7,484	431	7,484	513
Income Before Income from Equity Method Investments and Income Taxes	(6,532)	4,768	(3,360)	8,472
Income (Loss) from Equity Method Investments	1,957	1,374	3,716	2,933
Pre-Tax Income (Loss)	(4,575)	6,142	356	11,405
Identifiable Segment Assets	$ 316,192	$ 342,641	$ 316,192	$ 342,641