Revenues from Contracts with Customers (Schedule of Components of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	May 31, 2019	Jun. 30, 2018	May 31, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 750,206	$ 834,553	$ 1,320,193	$ 1,562,969
Revenue from other sources	760,165	409,273	1,385,190	841,968
Total revenues	1,510,371	1,243,826	2,705,383	2,404,937
Commissions and other fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	159,685	157,704	306,819	305,606
Total revenues	159,685	157,704	306,819	305,606
Investment banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	430,087	500,297	715,683	940,288
Total revenues	430,087	500,297	715,683	940,288
Manufacturing revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	90,237	114,735	165,662	213,100
Total revenues	90,237	114,735	165,662	213,100
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	70,197	61,817	132,029	103,975
Principal transactions
Disaggregation of Revenue [Line Items]
Revenue from other sources	240,189	53,755	486,371	199,418
Total revenues	240,189	53,755	486,371	199,418
Interest income
Disaggregation of Revenue [Line Items]
Revenue from other sources	445,967	327,314	832,811	602,536
Total revenues	445,967	327,314	832,811	602,536
Other
Disaggregation of Revenue [Line Items]
Revenue from other sources	$ 74,009	$ 28,204	$ 66,008	$ 40,014