Revenues from Contracts with Customers (Schedule of Components of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 780,079		$ 2,343,048
Revenue from other sources	678,898		1,520,866
Total revenues	1,458,977	$ 1,102,593	3,863,914	$ 3,735,702
Commissions and other fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	155,417		461,023
Total revenues	155,417	139,082	461,023	437,547
Investment banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	460,043		1,400,331
Total revenues	460,043	475,702	1,400,331	1,235,586
Manufacturing revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	94,029		307,129
Total revenues	94,029	81,939	307,129	243,482
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	70,590		174,565
Principal transactions
Disaggregation of Revenue [Line Items]
Revenue from other sources	116,204		315,622
Total revenues	116,204	84,143	315,622	725,780
Interest income
Disaggregation of Revenue [Line Items]
Revenue from other sources	336,736		939,272
Total revenues	336,736	$ 253,916	939,272	$ 726,972
Other
Disaggregation of Revenue [Line Items]
Revenue from other sources	$ 225,958		$ 265,972