Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Investment Banking [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	$ 385,303	$ 362,726	$ 1,289,154	$ 1,249,490
Investment Banking [Member] | Advisory Fees [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	320,885	305,949	1,090,309	1,047,259
Investment Banking [Member] | Underwriting Fees [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	17,598	11,440	61,428	62,784
Investment Banking [Member] | Commissions and Related Fees [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	46,820	45,337	137,417	139,447
Investment Management [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	12,650	12,678	37,452	36,603
Investment Management [Member] | Wealth Management [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	12,155	11,560	35,408	33,826
Investment Management [Member] | Institutional Asset Management [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	$ 495	$ 1,118	$ 2,044	$ 2,777