Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Investment Banking [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	$ 659,587	$ 484,335	$ 1,304,288	$ 919,583
Investment Banking [Member] | Advisory Fees [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	560,814	336,436	1,072,732	695,000
Investment Banking [Member] | Underwriting Fees [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	48,048	93,565	127,305	114,683
Investment Banking [Member] | Commissions and Related Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	50,725	54,334	104,251	109,900
Investment Management [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	16,183	12,953	31,132	25,700
Investment Management [Member] | Wealth Management [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	16,183	12,632	31,132	24,960
Investment Management [Member] | Institutional Asset Management [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	$ 0	$ 321	$ 0	$ 740